High pressure frozen oocytes have improved ultrastructure but reduced cleavage rates compared to conventionally fixed or vitrified oocytes

Context Live birth rates are lower for cryopreserved oocytes than for fresh IVF cycles, indicating a need for improved methodologies. Aims The aim of this study was to determine if high pressure freezing (HPF) could improve both ultrastructural preservation and cryopreserved oocyte quality when compared to conventional fixation and vitrification methods. Methods Sheep oocytes and embryos were prepared by HPF or vitrification, with or without cryoprotectants. Frozen oocytes were prepared for transmission electron microscopy or warmed, in vitro fertilised and the recovery and cleavage rates recorded. Key results Blastocyst rates were similar between fresh, HPF and vitrified embryos. HPF oocytes had improved ultrastructure compared to conventional fixation or vitrification, but had poorer survival and cleavage rates compared to vitrified oocytes. Freeze-substitution of cryopreserved oocytes and transmission electron microscopy demonstrated disruption of the oocyte ultrastructure in the presence of cryoprotectants. Conclusions Superior preservation of ultrastructure was observed in HPF oocytes compared to vitrification or conventional fixation methods. In the presence of CP, both embryos and oocytes could survive HPF and warming but oocytes had reduced development. Implications The HPF method has potential to be developed and lead to improved oocyte and embryo cryopreservation and outcomes for assisted reproduction.

The first week following insemination is the period of major pregnancy failure in pasture-grazed dairy cows

A 60% pregnancy success for inseminations is targeted to optimize production efficiency for dairy cows within a seasonal, pasture-grazed system. Routine measures of pregnancy success are widely available but are limited, in practice, to a gestation stage beyond the first 28 d. Although some historical data exist on embryonic mortality before this stage, productivity of dairy systems and genetics of the cows have advanced significantly in recent decades. Accordingly, the aim was to construct an updated estimate of pregnancy success at key developmental stages during the first 70 d after insemination. Blood samples were collected for progesterone concentrations on d 0 and 7. A temporal series of 4 groups spanning fertilization through d 70 were conducted on 4 seasonal, pasture-grazed dairy farms (n = 1,467 cows) during the first 21 d of the seasonal breeding period. Morphological examination was undertaken on embryos collected on d 7 (group E7) and 15 (group E15), and pregnancy was diagnosed via ultrasonography on approximately d 28 and 35 (group E35) as well as d 70 (group E70). Fertilization, embryo, and fetal evaluation for viability established a pregnancy success pattern. Additionally, cow and on-farm risk factor variables associated with pregnancy success were evaluated. We estimated pregnancy success rates of 70.9%, 59.1%, 63.8%, 62.3%, and 56.7% at d 7, 15, 28, 35, and 70, respectively. Fertilization failure (15.8%) and embryonic arrest before the morula stage (10.3%) were the major developmental events contributing to first-week pregnancy failures. Embryo elongation failure of 7% contributed to pregnancy failure during the second week. The risk factors for pregnancy success that were related to the cows included interval between calving and insemination, and d-7 plasma progesterone concentrations, whereas insemination sire was associated with pregnancy outcome. Most pregnancy failure occurs during the first week among seasonal-calving pasture-grazed dairy cows.

Development of a GnRH-PGF2α-progesterone-based synchronization protocol with eCG for inducing single and double ovulations in beef cattle

Experiments were designed to investigate the effect of different doses and timing of an eCG treatment given during GnRH-based synchronization protocols on follicular dynamics and fertility in cattle. In Exp. 1, Angus heifers (n = 50) received a 7-d Ovsynch + progesterone protocol (on d 0, GnRH and progesterone insert were administered; on d 7, progesterone insert was removed and PGF2α was injected; and on d 9.5, GnRH was injected 56 h after progesterone removal) with eCG (0, 300, 500, 700, or 1,000 IU) administered on d 7. In Exp. 2, Angus cows (n = 27) received the same protocol as Exp. 1 and were assigned randomly to receive 0 or 400 IU eCG i.m. on d 2 or 7. In Exp. 3, Angus cows (n = 18) received a 6-d Ovsynch + progesterone protocol and were randomly assigned to receive 0 or 800 IU eCG on d 3 of the protocol (Exp. 3a). A pilot field trial was also performed using the same treatments in suckled Angus-cross cows (n = 72; Exp. 3b). In Exp. 4, beef heifers (n = 200) were assigned randomly to the same treatments as in Exp. 3, but the second GnRH was not given, with Holstein bulls introduced on d 6. In Exp. 5, Angus cows (n = 12) received the same treatment as in Exp. 3, but were not inseminated. Progesterone concentrations were assessed in plasma collected during the estrous cycle following synchronization. Ultrasonography was used to monitor ovarian dynamics and to diagnose pregnancy. In Exp. 1, the mean number of ovulations was affected (P < 0.02) by the dose of eCG and the stage of follicular development when administered. Treatment with eCG on d 2 tended (P < 0.08) to extend the interval from PGF2α to ovulation, but was not successful in inducing double ovulations. In contrast, eCG on d 3 increased (P < 0.01) the number of cows with double ovulation when administered i.m. and increased (P < 0.04) pregnancy rate in single ovulating heifers after bull breeding (68.0 vs. 53.1%). This treatment also elevated progesterone concentrations during the estrous cycle following synchronization. Thus, the mechanism by which administration of eCG on d 3 of the synchronization increased pregnancy rates may be through supporting development of a healthy follicle and subsequent corpus luteum capable of secreting increased concentrations of progesterone during early pregnancy. In conclusion, strategic administration of eCG during a synchronization protocol can be used to improve reproductive performance through increased pregnancy rates in single ovulating animals as well as the induction of twin ovulations for twinning.

Effect of age, weight, and sire on embryo and fetal survival in sheep

The goal was to estimate the heritabilities and genetic variances for embryo and fetal survival (ES) in sheep along with the effect of premating ewe weight, age, and bilateral or unilateral ovulation on ES. The data consisted of 11,369 records on ovulation rate and litter size. Statistical models for ES included year and ovulation rate as fixed effects, premating ewe weight, and age as covariates, and sire of embryo, maternal grandsire (MGS), and permanent maternal environmental effects of the ewe as random effects. The variance components were estimated using REML. In ewes that survived to yr 6, the mean litter size was 1.87, 2.05, 2.01, 2.07, and 1.91 ± 0.04 in ewes of age 2, 3, 4, 5, and 6 yr, respectively. Litter size was less in ewes of age 2 and 6 yr compared to ewes of age 3, 4, and 5 yr (P < 0.01). Ovulation rate was lower at age 2 yr and increased from age 2 to 6 yr (P < 0.05). Two-year-old ewes had lower ES than 3-yr-old ewes (P < 0.01) and the probability of ES decreased after age 3 yr (P < 0.01). Thus, ES contributes significantly to lower fertility in 2-yr-old ewes. In ewes with high ovulation rates (i.e., 5 corpora lutea, CL), more balanced ovulations (i.e., 2 or 3 CL on each ovary) tended (P = 0.06) to be associated with increased ES. A quadratic relationship was observed between ewe weight and litter size (P < 0.01) and a positive linear relationship between premating ewe weight and ovulation rate (P < 0.01). A quadratic effect of ewe weight on ES was observed, with decreased ES for low and high ewe weights (P < 0.01). The optimal ewe weight for ES increased with ovulation rate, which is consistent with the requirement of greater body reserves for maintaining a larger number of fetuses during gestation. A quadratic relationship between ewe weight and the probability that a ewe is able to maintain a pregnancy was also observed (P < 0.05). Pregnancy loss is due to failure of the embryo or fetus or failure of the dam to maintain the pregnancy. The sire of the embryo only influences the embryo, whereas the MGS influences both the ewe and the embryo. The heritability for the direct additive effect on ES in ewes that lambed was 0.0081 ± 0.0139, and the heritability for the maternal additive effect was 0.0447 ± 0.0242. The permanent maternal environmental variance component was significant and explained 8.5% of the phenotypic variance. Thus, genetically, the dam's ability to maintain a pregnancy has 5.5 times the effect on pregnancy loss than the embryo's ability to survive, and this, in turn, was only half the size of the permanent environmental effect. Therefore, selection among dams based on the mean embryonic survival of their embryos will provide an effective way to improve embryonic survival.

Heterozygous Inverdale ewes show increased ovulation rate sensitivity to pre-mating nutrition

This study aimed to determine whether ewes heterozygous (I+) for the Inverdale mutation of the bone morphogenetic protein-15 (BMP15) gene with high natural ovulation rate (OR) show similar sensitivity to nutritional manipulation as non-carriers (++). Increasing pre-mating nutrition results in OR increases in sheep, but whether this effect occurs in ewes with naturally high OR is unknown. Over 2 years, I+ or ++ ewes were given high (ad libitum) or control (maintenance) pasture allowances for 6 weeks prior to mating at a synchronised oestrus, with OR measured 8 days later. The high group increased in weight compared with controls (+5.84 kg; P < 0.01), accompanied by increased OR (+19%; P < 0.01). As well as having higher OR (+45%; P < 0.01), I+ ewes responded to increased feed with a larger proportional increase in OR (+27%; P < 0.01) compared with the response in ++ ewes (+11%; P < 0.05), suggesting an interaction between BMP15 levels and nutritional signals in the follicle to control OR. Although litter size increases only tended to significance (+12%; P = 0.06), extra feed resulted in over 50% of I+ ewes giving birth to more than three lambs, compared with 20–31% of I+ ewes on maintenance rations. This information can guide feed management of prolific Inverdale ewes prior to breeding.

27 FOLLICULAR RESPONSE TO DIFFERENT eCG DOSES IN AN OVSYNCH + PROGESTERONE PROTOCOL IN BEEF HEIFERS

An experiment was designed to evaluate the effect of different doses of eCG on ovarian follicular dynamics in heifers treated with a Ovsynch plus progesterone protocol. Twenty-five cyclic yearling Black Angus heifers (373.0 ± 35.7 kg), in 2 replicates, received an injection of 100 μg of GnRH (Ovurelin, Bomac Laboratories Ltd., Auckland, New Zealand) i.m. and an intravaginal progesterone device (1.38 g of progesterone; Eazi-Breed CIDR, Pfizer Animal Health, New Zealand) on Day 0 (beginning of the experiment), followed by 500 μg of cloprostenol (PGF, Estrumate, Intervet/Schering-Plough Animal Health, Auckland, New Zealand) i.m. on Day 7, and a second 100 μg of GnRH injection given i.m. on Day 9 (56 h after PGF). At the time of PGF treatment, heifers were randomly assigned to 5 treatment groups to receive 0, 300, 500, 700, or 1000 IU of eCG (Folligon, Intervet/Schering-Plough Animal Health) i.m. Heifers were monitored by ultrasonography (Aloka 900-SSD equipped with a 7.5-MHz linear-array transducer; Aloka, Tokyo, Japan) daily from Day 0 to 9 (GnRH), and then every 12 h until ovulation. Data were analyzed by one-way ANOVA or Kruskall-Wallis test, and means or ranks were compared with LSD or Wilcoxon rank sum tests, respectively. Because a replicate effect was observed (P < 0.05) in the size of the dominant follicle at the second GnRH and prior to ovulation, replicate effect was included in the analysis. The luteal area at PGF treatment was significantly greater (P < 0.01) in heifers that ovulated (750.0 ± 97 mm2) in response to the first GnRH treatment than in those that did not (301.6 ± 42.7 mm2). The diameter of the dominant follicle at the time of PGF treatment was also greater (P < 0.05) in ovulating (11.2 ± 0.4 mm) than in nonovulating (9.7 ± 0.5 mm) heifers. The interval from the first GnRH treatment to the emergence of the next follicular wave was longer (P = 0.50) and more variable in heifers that did not ovulate (2.9 ± 0.4 d; n = 27) than in those that ovulated (1.9 ± 0.2 d; n = 23). There was no effect (P < 0.37) of eCG on the interval from PGF to ovulation (86 ± 1.9 h). The number of ovulations after the second GnRH was higher (P = 0.01) in the group of heifers treated with 1000 IU of eCG (1.8 ± 0.4) than in the other groups (1.0 ± 0.0; 1.1 ± 0.1; 1.2 ± 0.1; 1.0 ± 0.1). There was an effect of day of follicular wave emergence on the number of ovulations (P < 0.01). Heifers with a wave emerging 1 to 3 days after the first GnRH (n = 37), had one ovulation (1.0 ± 0.0), whereas heifers with a wave emerging on Day 4 (3 out of 4 heifers) and Days 5 to 7 (n = 9), ovulated 2 or more follicles. In summary, the multiple ovulation effect occurred when eCG was given to heifers with a follicular wave emerging on or after Day 4, and was potentiated when heifers received 1000 IU of eCG. Although the dose of eCG given at the time of PGF treatment in an Ovsynch program has a significant effect on follicular development, the time of emergence of the dominant follicle appeared to be more important in the ovulation of preovulatory follicle/s after the eCG and the second GnRH treatment.

36 FOLLICULAR DYNAMICS IN PROLIFIC SHEEP: PGF-BASED ESTRUS SYNCHRONIZATION

A study was designed to compare the effect of a prostaglandin-based synchronization protocol on ovarian follicular dynamics in sheep with the FecB (Booroola) mutation. Forty dry Romney sheep (57.6 ± 7.3 kg; 6.1 ± 1.1 years) were randomly selected from both Invermay Booroola (BB; n = 20) and commercial (non-FecB carriers, ++; n = 20) flocks. All ewes had their estrous cycles synchronized with 2 i.m. injections of PGF (150 μg of cloprostenol, Estrumate, Schering-Plough Coopers Animal Health Ltd., New Zealand) administered 7 days apart. Ewes were monitored by transrectal ultrasonography (Aloka 900-SSD and a 7.5-MHz linear-array transducer, Aloka, Tokyo, Japan) daily from Day -2 to the day of ovulation. Data were analyzed by Student’s t-test or Wilcoxon Rank Sum test. Variances were compared with Barlett’s test. Paired t-test compared the number of preovulatory follicles in each genotype after PGF treatments and intervals from PGF to ovulation after PGF. Data are presented as mean (± SEM). The number of corpora lutea (CL) and total CL area at the time of the first and second PGF treatment were 4.4 ± 0.6; 5.7 ± 1.4 and 672.1 ± 133.5 mm2; 999.0 ± 145.9 mm2 in the BB and 2.1 ± 0.2; 2.1 ± 0.5 and 342.3 ± 60.7 mm2; 401.3 ± 68.6 mm2 in ++ ewes, respectively. These 2 variables were higher (P < 0.01) at both PGF injections in the BB than in the ++ ewes, except the CL area at the time of first PGF treatment (P = 0.15). The largest follicle diameter at the time of the first and second PGF treatments was smaller (P < 0.003) in BB (4.1 ± 0.3 mm; 3.5 ± 0.2 mm) than in ++ (5.3 ± 0.3 mm; 5.8 ± 0.1 mm) ewes. The median and mean number of follicles that ovulated after the first and second PGF treatment were higher (P < 0.0001) in BB (6 & 7; 5.7 ± 0.3; 6.9 ± 0.3; difference = 1.2 ± 0.4; P < 0.003) than in the ++ (2 & 2; 2.1 ± 0.1; 2.1 ± 0.1) sheep. The luteal area at the time of first and second PGF in both BB and ++ did not differ (P = 0.3). The intervals from the first and second PGF to the respective ovulations did not differ (P > 0.61) between BB (3.4 ± 0.2; 3.0 ± 0.3d) and ++ (3.5 ± 0.2d; 3.0 ± 0.1d) ewes. However, interval from the second PGF to ovulation was more variable (P = 0.002) in the BB than in the ++ ewes. Data of both groups were combined and a mean significant difference of 0.6 ± 0.2d (P < 0.003) was found between the first and second PGF-to-ovulation intervals. The interval from the first PGF to emergence of the next follicular wave was shorter (P < 0.02) and more variable (P < 0.03) in the BB (2.7 ± 0.4d) than in the ++ (3.5 ± 0.2 d) group. Preovulatory follicles were smaller in Booroola, but higher in number, than in ++ ewes, whereas the luteal area was similar. Within the BB ewes, the higher number of follicles that ovulated after the second PGF than after the first injection may be due to a higher follicular response to an elevated rebound in circulating FSH after the first PGF. A high number of growing follicles of the first follicular wave may also have contributed to this event. These findings warrant further research aimed at the study of the interaction between FSH and follicle dynamics in estrus synchronized sheep carrying the FecB mutation.

Morphological development and characterization of aromatase and estrogen receptors alpha and beta in fetal ovaries of cattle from days 110 to 250

To better understand the role of estradiol-17beta in fetal ovarian development, presence and localization of cytochrome P450 aromatase (P450arom) and estrogen receptors alpha (ERalpha) and beta (ERbeta) proteins were characterized in fetal ovaries of cattle using immunohistochemistry. Fetal cattle ovaries were collected from an abattoir and sorted into fetal age groups (days 110, 130, 150, 170, 190, 210, 230, 250+) based on crown-rump length. In addition to immunohistochemistry, morphological analysis of ovarian and follicular formation was made. Ovaries appeared lobular at day 110, but by the end of gestation (day 250+) ovaries were oval-shaped similar to those found in adult animals. Ovarian structures within different lobes appeared to be at different developmental stages. At day 110, oocytes and pre-granulosa cells were observed in ovigerous cords that were still open to the surface epithelium. Most ovigerous cords appeared to be closed to the surface epithelium on day 130, all closed by day 150 and were no longer present at day 210. Ovarian follicles were classified as follows: Type 1(primordial): single layer of flattened granulosa cells, Type 1a (transitory): single layer of mixed flattened and cuboidal granulosa cells, Type 2 (primary): at least one but less than two layers of cuboidal granulosa cells, Type 3 (small preantral): two to three layers of granulosa cells, Type 4 (large preantral): four to six layers of granulosa, and the theca layer is forming around the follicle, Type 5 (antral): contain greater than six layers of granulosa cells, several layers of theca cells and the antrum has formed. Type 1 follicles were observed in day 110 ovaries. Follicle Types 1a and 2 were first observed on day 130. Type 3 follicles were first observed on day 150 and Types 4 and 5 were first observed on day 170. P450arom protein was localized in granulosa cells of follicle Types 2-5 and cells of rete tubules throughout the experimental period. There was punctate expression within stroma and rete masses. There was ERalpha protein localization in pre-granulosa cells and germ cells of ovigerous cords and all surface epithelial cells. There was also localization in granulosa cells and oocytes of all follicle types and cells of rete tubules. There was punctate ERalpha protein expression in stroma and rete masses. ERbeta protein was localized in pre-granulosa cells and germ cells of ovigerous cords. Expression was also localized to granulosa cells of all follicle types and cells of rete tubules. ERbeta protein was punctate in oocytes of follicles, surface epithelial cells, stroma and rete masses. Thus, the fetal ovary of cattle has the steroidogenic enzyme (P450arom) to convert androgens to estradiol-17beta, and estrogen receptors alpha and beta to facilitate an estrogen response within the fetal ovary.

272. Signalling pathways involved in mouse GDF9 and BMP15 stimulated thymidine uptake by rat granulosa cells

The oocyte-secreted factors growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15) are essential for ovarian follicular growth and development. Understanding the molecular mechanisms of these factors could assist with the development of future products for fertility control. Thymidine uptake by rat granulosa cells is stimulated cooperatively by GDF9 and BMP15. Inhibitors of the activin receptor-like kinase (ALK) 4,5,7 and the nuclear factor kappaB (NFKB) second messenger pathways block ovine GDF9 and BMP15 stimulated thymidine incorporation. The ALK 4,5,7 receptor pathway is known to be essential for the cooperative effects of mouse (m)GDF9 and mBMP15 on thymidine incorporation but the role of other pathways has yet to be determined, which was the focus of this study. Inhibitors of NFKB (Sn50; 10µg/mL), ALK 2,3,6 receptor (Dorsomorphin; 1µM), p38 mitogen-activated protein kinase (p38 MAPK; SB239063; 5 µM) and c-Jun-N-terminal kinase (JNK; TAT-TI-JIP153–163; 5 µM) pathways were each cultured with recombinant mGDF9 (25 ng/mL) and mBMP15 (6 ng/mL) in a rat granulosa cell [3H]-thymidine bioassay. The p38 MAPK inhibitor caused partial inhibition of thymidine uptake but this appeared to be non-specific as a similar level of suppression was observed in the control cultures. Neither the ALK 2,3,6 receptor nor the NFKB pathway inhibitors had any effect on mGDF9 and mBMP15 stimulated thymidine uptake. The JNK inhibitor showed a 1.7-fold increase in stimulation above the mGDF9 and mBMP15 effect (P < 0.01) but a similar stimulation was also observed in some controls. This differs from the results observed with ovine GDF9 and BMP15 where thymidine uptake was completely blocked by the NFKB inhibitor and the JNK inhibitor had no effect. In conclusion, the molecular mechanisms of GDF9 and BMP15 function are dependent on the species of origin of the growth factor and therefore caution is needed when extrapolating findings from one species to another.

Control of ovarian follicular development to the gonadotrophin-dependent phase: a 2006 perspective

In sheep, as in other mammals, ovarian follicular growth is regulated mainly by intraovarian growth factors during early development with pituitary hormones increasingly important during the final phases to ovulation. Most follicles are present as primordial structures and these express many hundreds of genes that fulfil an array of housekeeping and signalling functions. Once growth has been initiated, at least two oocyte-derived growth factors, namely growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15), are critical for ongoing development to ovulation, most likely by regulating the proliferative and differentiative functions of adjacent follicular cells. In sheep, the granulosa cell populations double some 12-14 times and a well-defined thecal layer differentiates before antrum formation and the time taken to complete this process varies between 50 -150 days with very little follicular atresia. During preantral growth, FSH and LH receptors coupled to the cyclic AMP second messenger system develop in granulosa and thecal cells respectively. From the late preantral stage, GDF9, BMP15 and perhaps other factors are thought to regulate gene expression in cumulus cells to enhance metabolic cooperativity with the oocyte and in mural granulosa cells to regulate their responses to pituitary hormones. In sheep, antral follicular development is characterized by a much faster rate of growth, additional increases in the numbers of granulosa (4-5 more doublings) and thecal/cells, an increased level of steroid and inhibin secretion in response to FSH and LH, but also by most follicles undergoing atresia. The final number of follicles that go on to ovulate is dependent upon FSH as well as the intrafollicular concentrations of GDF9 and BMP15.

Oocyte-expressed genes affecting ovulation rate

From examination of inherited patterns of ovulation rate in sheep, several breeds have been identified with point mutations in two growth factor genes (BMP15 and GDF9) and a related receptor (ALK6) that are expressed in oocytes. Five different point mutations have been identified in the BMP15 gene, one in GDF9 and one in ALK6. Animals heterozygous for these mutations or heterozygous for two of these mutations or homozygous for the ALK6 mutation have higher ovulation rates (i.e. +0.6-10) than their wild-type contemporaries. Animals homozygous for the BMP15 or GDF9 mutations are sterile due to arrested follicular development from the primary stage of growth. The BMP15 and GDF9 mutations are thought to result in reduced levels of mature protein or altered binding to cell-surface receptors. In sheep, GDF9 mRNA is present in germ cells before and after ovarian follicular formation as well as throughout follicular growth, whereas BMP15 mRNA is found in oocytes only from the primary stage of growth. Also ALK6 together with related cell-surface receptors such as ALK5 and BMPRII mRNA are present in oocytes at most, if not all, stages of follicular growth. Both GDF9 and BMP15 proteins are present in follicular fluid indicating that they are secreted products. Immunisation of sheep with GDF9 or BMP15 peptides shows that both growth factors are essential for follicular development, ovulation and/or corpus luteum formation. In animals with the ALK6 mutation, ovarian follicles undergo precocious maturation leading to three to seven follicles ovulating at smaller diameters without any increase above wild-types in the ovarian secretions of steroid or inhibin. One important consequence of the ALK6 mutation appears to be a decreased ability of some BMPs to inhibit differentiation of follicular cells. Current findings in sheep suggest that BMP15, GDF9 and ALK6 are targets for new methods of fertility regulation in some mammals.

The role of proteins of the transforming growth factor-beta superfamily in the intraovarian regulation of follicular development

Ovarian follicular development occurs in a hierarchical manner with each follicle having a unique biochemical composition at any moment in time. It has long been understood that a precise coordination between the growth and maturation of the oocyte and adjacent follicular cells (i.e. somatic cells) is essential in order to produce an oocyte that is fully competent to undergo fertilization and embryo development. In addition to the critical endocrine signalling pathways between the hypothalamus, pituitary and ovary, it is now evident that the oocyte itself is important in influencing the microenvironment of the developing follicle by regulating, via paracrine and autocrine mechanisms, its own maturation as well as somatic cell proliferation, differentiation and ovulation rate. Several of the key oocyte-derived regulating factors are members of the transforming growth factor-beta (TGF-beta) superfamily and to date the best understood are growth differentiation factor 9 (GDF9), bone morphogenetic protein 15 (BMP15) and BMP6. Significant species differences appear to exist in the relative importance of these growth factors and much remains to be elucidated about their roles in the human ovary. More information on the roles of these factors during ovarian follicular development is likely to advance new therapeutic applications for management of fertility as well as our understanding of how better to assess oocyte quality.

252. Morphometric and histological analysis of ovaries from sheep heterozygous for the prolific woodlands allele

Woodlands are a line of Coopworth sheep with a novel, imprinted X-linked fecundity allele resulting in ovulation rates about 0.40 higher than wild-type animals. Daughters of progeny tested sires with and without the gene were studied. Previously, lambs heterozygous for the Woodlands allele were found to have larger ovaries and more antral (i.e. type 5) but not preantral (i.e. types 1–4) follicles than in wild-type contemporaries. The large ovary phenotype was found to be transient and was absent after puberty. However, based on follow-up studies it was evident that the large ovary phenotype was not strongly associated with the Woodlands fecundity allele. Thus, it was uncertain whether animals carrying the Woodlands gene had different follicular populations compared to wild-type controls. To address this question, follicular populations were compared in adult ewes heterozygous for the Woodlands allele with age-matched controls. Using standard morphometric methods and histological analysis, no differences were observed in the mean numbers of types 1, 1a, 2, 3 and 4 preantral follicles between the genotypes. Furthermore, no differences were observed between genotypes in follicular or oocyte diameters for any follicular type. The adult Woodlands carrier ewes had twice as many small type 5 follicles (< 1mm) when compared to wild-type contemporaries although no difference was seen in the numbers of antral follicles > 1mm in diameter. In addition, antrum formation occurred at a smaller follicular diameter in the heterozygous Woodlands animals. Therefore, the increased number of antral follicles observed in both lambs and adult ewes suggests that this difference in pattern of follicular development is associated with the X-linked fecundity allele. This novel phenotype of early antrum formation and larger number of small preantral follicles differs from that observed in sheep with the Inverdale or Booroola mutations, suggesting that a different mechanistic pathway is involved. Acknowledgements: The Marsden Fund, FRST and Ovita.

The oocyte and its role in regulating ovulation rate: a new paradigm in reproductive biology

Ovulation rate in mammals is determined by a complex exchange of hormonal signals between the pituitary gland and the ovary and by a localised exchange of hormones within ovarian follicles between the oocyte and its adjacent somatic cells. From examination of inherited patterns of ovulation rate in sheep, point mutations have been identified in two oocyte-expressed genes, BMP15 (GDF9B) and GDF9. Animals heterozygous for any of these mutations have higher ovulation rates (that is, + 0.8–3) than wild-type contemporaries, whereas those homozygous for each of these mutations are sterile with ovarian follicular development disrupted during the preantral growth stages. Both GDF9 and BMP15 proteins are present in follicular fluid, indicating that they are secreted products.In vitrostudies show that granulosa and/or cumulus cells are an important target for both growth factors. Multiple immunisations of sheep with BMP15 or GDF9 peptide protein conjugates show that both growth factors are essential for normal follicular growth and the maturation of preovulatory follicles. Short-term (that is, primary and booster) immunisation with a GDF9 or BMP15 peptide-protein conjugate has been shown to enhance ovulation rate and lamb production. In summary, recent studies of genetic mutations in sheep highlight the importance of oocyte-secreted factors in regulating ovulation rate, and these discoveries may help to explain why some mammals have a predisposition to produce two or more offspring rather than one.

Physiology of GDF9 and BMP15 signalling molecules

Two related oocyte-derived members of the transforming growth factor-beta (TGF-beta) superfamily, namely growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15, also known as GDF9B), have recently been shown to be essential for ovarian follicular growth. In addition, both proteins have been shown to regulate ovulation rate in sheep, and although it is evident that these growth factors interact both with one another and with other intra- and extra-ovarian factors, the precise mechanisms by which they influence follicular growth and ovulation rate have not been thoroughly elucidated.

Oocyte-derived growth factors and ovulation rate in sheep

The physiological mechanisms controlling ovulation rate in mammals involve a complex exchange of endocrine signals between the pituitary gland and the ovary, and a localized exchange of intraovarian hormones between the oocyte and its adjacent somatic cells. The discoveries in sheep of mutations in bone morphogenetic protein 15 (BMP15) and bone morphogenetic protein receptor type IB (BMPR-IB) together with recent findings on the physiological effects of growth differentiation factor 9 (GDF9) and BMP15 on follicular development and ovulation rate highlight some important differences in the way in which the oocyte may function in mammals with different ovulation rate phenotypes. In sheep, BMP15 and GDF9 have each been shown to be essential for the early and later stages of follicular development. In addition, ovulation rate is sensitive to changes in the dose of either of these two oocyte-derived growth factors. These findings are in contrast to those reported for mice in which GDF9, but not BMP15, is essential for follicular development. The evidence to date is consistent with the hypothesis that the oocyte plays a central role in regulating key events in the process of follicular development and hence, is important in determining ovulation rate. Moreover, it appears that the mechanisms that the oocyte uses to control these processes differ between species with low and high ovulation rate phenotypes.

Expression of the FcRn receptor (alpha and beta) gene homologues in the intestine of suckling brushtail possum (Trichosurus vulpecula) pouch young

The neonatal IgG transporter FcRn consists of two chains, FcRn alpha and beta (also known as beta(2) microglobulin), and is involved in transferring IgG molecules across both mammary and intestinal epithelial cells. Developmental changes in FcRn IgG alpha and beta chain mRNA levels were investigated in the gut of brushtail possum (Trichosurus vulpecula) pouch young (PY) using Northern hybridisation. FcRn alpha transcripts were detected in the PY proximal intestine at all times examined, between days 1 and 195 of post-natal life, with increased levels detected from around day 110. The beta(2) microglobulin transcript levels in the PY proximal intestine were low to undetectable until day 110 of post-natal life and then increased dramatically after day 159. Both the FcRn alpha and beta gene transcripts were detected in a wide range of tissues in the adult possum (>365 days). Genomic sequences located 5' to the start of transcription of the FcRn alpha and beta(2) microglobulin genes were cloned and analysed for predicted cis-acting transcription control elements. Both the FcRn alpha and beta(2) microglobulin genomic sequences contained STAT5 binding motifs consistent with the transcription of both genes being modulated by prolactin. Using in situ hybridisation, the FcRn alpha and beta(2) microglobulin transcripts were localised to the epithelial cells of the PY intestine. However, no prolactin receptor transcripts were detected in the same epithelial cells suggesting that the observed changes in FcRn alpha and beta(2) microglobulin gene expression in the proximal intestine are not modulated directly by prolactin. The results are consistent with the hypothesis that changes in FcRn alpha and beta(2) microglobulin gene expression take place in the possum PY intestine to accommodate changes in maternal milk composition to meet the changing immunological demands of the PY.

Genetic mutations influencing ovulation rate in sheep

Ovulation rate in mammals is determined by a complex exchange of endocrine signals between the pituitary gland and the ovary, and by paracrine signals within ovarian follicles between the oocyte and its adjacent somatic cells. One approach to identifying factors regulating ovulation rate is to find mutations that influence the target phenotype and, in this context, sheep are proving to be remarkable experimental models. Recently, in three sheep families, namely Inverdale, Hanna and Booroola, the inherited mutation was mapped to a specific region of the sheep X chromosome (Inverdale, Hanna) or sheep chromosome 6 (Booroola) and in each, a point mutation was identified in genes from the bone morphogenetic protein (BMP) relatives of the transforming growth factor beta superfamily or their receptors. In Inverdale (I) and Hanna (H) sheep, separate point mutations were identified in the BMP15 gene corresponding to sites in the mature peptide coding region of the BMP15 growth factor (also known as growth differentiation factor 9B; GDF9B). Expression of the BMP15 gene was located exclusively in oocytes from the primary stage of follicular growth. There is a complete block of normal follicular development in females carrying two copies of the Inverdale mutation (II), two copies of the Hanna mutation (HH), or one copy of each mutation (HI). Increased ovulation rates are found in females with only one copy of either mutation (I+ or H+). In Booroola sheep, a point mutation was identified in the highly conserved intracellular serine threonine kinase signalling domain of the BMP-1B receptor. Within the ovary, this gene is expressed in oocytes in primordial and pre-antral follicles and in granulosa cells from the primary stage of growth as well as in corpora lutea. The effect of the Booroola mutation is additive for ovulation rate: animals with one copy of the mutation have an ovulation rate of 3 or 4, whereas those with two copies have an ovulation rate of between 5 and 14. Physiological studies of the above mutations demonstrate that the oocyte plays an active role with respect to its adjacent somatic cells during follicular development and support the hypothesis that the oocyte has a significant influence on the number of follicles that proceed to ovulation.

Bmp15 mutations and ovarian function

BMP15, also known as growth and differentiation factor 9B (GDF9B), is a member of the transforming growth factor beta superfamily (TGFbeta) which in humans, rodents and sheep is expressed exclusively in the oocyte. BMP15 is closely related to GDF9, another oocyte-specific member of this superfamily which has been shown to be essential for early ovarian folliculogenesis. Inactivation of the BMP15 gene in mice has shown only minor effects on fertility. However, Inverdale and Hanna lines of sheep carry naturally occurring mutations in BMP15 which highlight differences in the action of this gene between mice and other mammals. Sheep which are heterozygous show an increase in ovulation rate whereas homozygotes are infertile. The granulosa cell receptor which mediates the BMP15 response has not yet been identified, but the discovery that a point mutation in the BMP1B receptor in Booroola sheep is responsible for increased ovulation rate highlights the importance of the TGFbeta signalling molecules in early folliculogenesis.

Ontogeny of steroidogenesis in the fetal sheep gonad

The aim of this study was to determine 1) the time of onset and cellular localization of gene expression for steroidogenic factor-1 (SF-1), steroidogenic acute regulatory protein, 3beta-hydroxysteroid dehydrogenase/Delta(5),Delta(4) isomerase (3beta-HSD), and the cytochrome P450 enzymes for cholesterol side-chain cleavage (P450(scc)), 17alpha-hydroxylase (P450(17alphaOH)), and aromatase (P450(arom)) during gonadal development; and 2) the amount of progesterone, androstenedione, testosterone, and 17beta-estradiol present in the fetal sheep gonad. Fetuses were collected on Days 24, 26, 28, 30, 32, 35, 40, 55, and 75 of gestation, and gene expression was determined by in situ hybridization. The steroid content of gonads collected on Days 30, 35, 55, and 75 of gestation was determined by RIA. Developing gonads collected from both male and female fetuses were steroidogenically active around the time of morphological sexual differentiation. In the female, the steroidogenic cells were initially located at the boundary of the cortex and medulla but become increasingly restricted to the mesonephric-derived cell streams. In the male, once tubules were identifiable, steroidogenesis was restricted to the interstitial regions. Interestingly, expression of both SF-1 and 3beta-HSD was observed prior to morphological sexual differentiation. In addition, expression of both of these genes was more widespread than the other genes in both males and females.

Highly prolific Booroola sheep have a mutation in the intracellular kinase domain of bone morphogenetic protein IB receptor (ALK-6) that is expressed in both oocytes and granulosa cells

The Booroola fecundity gene (FecB) increases ovulation rate and litter size in sheep and is inherited as a single autosomal locus. The effect of FecB is additive for ovulation rate (increasing by about 1.6 corpora lutea per cycle for each copy) and has been mapped to sheep chromosome 6q23-31, which is syntenic to human chromosome 4q21-25. Bone morphogenetic protein IB (BMP-IB) receptor (also known as ALK-6), which binds members of the transforming growth factor-beta (TGF-beta) superfamily, is located in the region containing the FecB locus. Booroola sheep have a mutation (Q249R) in the highly conserved intracellular kinase signaling domain of the BMP-IB receptor. The mutation segregated with the FecB phenotype in the Booroola backcross and half-sib flocks of sheep with no recombinants. The mutation was not found in individuals from a number of sheep breeds not derived from the Booroola strain. BMPR-IB was expressed in the ovary and in situ hybridization revealed its specific location to the oocyte and the granulosa cell. Expression of mRNA encoding the BMP type II receptor was widespread throughout the ovary. The mutation in BMPR-IB found in Booroola sheep is the second reported defect in a gene from the TGF-beta pathway affecting fertility in sheep following the recent discovery of mutations in the growth factor, GDF9b/BMP15.

Steroidogenic acute regulatory protein and peripheral-type benzodiazepine receptor associate at the mitochondrial membrane

Steroidogenic acute regulatory protein (StAR) and peripheral-type benzodiazepine receptor (PBR) have both been implicated in the transport of cholesterol across mitochondrial membranes in steroidogenic cells. Therefore, we hypothesized that StAR and PBR were associated in this process. To test this hypothesis, we measured fluorescence energy transfer (FET) between these proteins by fusing enhanced green fluorescent protein (GFP, donor fluorophore) and yellow fluorescent protein (YFP, acceptor fluorophore) to the C-terminus of ovine StAR (37GFP) and ovine PBR (PBRYFP), respectively. These intrinsically fluorescent proteins were stably transfected into Cos-7 cells and determined to be biologically active. For FET to occur the appropriate fluorescent molecules need to be <100 A from each other. We observed 22.0 +/- 0.9% energy transfer efficiency for 37GFP and PBRYFP, a 4.9 fold increase above non-specific energy transfer between free GFP and PBRYFP (p <.0001). Thus, it appears that StAR and PBR are closely associated in mitochondrial membranes and that these molecules may interact in the transportation of cholesterol.

Prostaglandin metabolism in the ovine corpus luteum: catabolism of prostaglandin F(2alpha) (PGF(2alpha)) coincides with resistance of the corpus luteum to PGF(2alpha)

To examine possible mechanisms involved in resistance of the ovine corpus luteum to the luteolytic activity of prostaglandin (PG)F(2alpha), the enzymatic activity of 15-hydroxyprostaglandin dehydrogenase (PGDH) and the quantity of mRNA encoding PGDH and cyclooxygenase (COX-2) were determined in ovine corpora lutea on Days 4 and 13 of the estrous cycle and Day 13 of pregnancy. The corpus luteum is resistant to the action of PGF(2alpha) on Days 4 of the estrous cycle and 13 of pregnancy while on Day 13 of the estrous cycle the corpus luteum is sensitive to the actions PGF(2alpha). Enzymatic activity of PGDH, measured by rate of conversion of PGF(2alpha) to PGFM, was greater in corpora lutea on Day 4 of the estrous cycle (P < 0.05) and Day 13 of pregnancy (P < 0.05) than on Day 13 of the estrous cycle. Levels of mRNA encoding PGDH were also greater in corpora lutea on Day 4 of the estrous cycle (P < 0. 01) and Day 13 of pregnancy (P < 0.01) than on Day 13 of the estrous cycle. Thus, during the early estrous cycle and early pregnancy, the corpus luteum has a greater capacity to catabolize PGF, which may play a role in the resistance of the corpus luteum to the actions of this hormone. Levels of mRNA encoding COX-2 were undetectable in corpora lutea collected on Day 13 of the estrous cycle but were 11 +/- 4 and 44 +/- 28 amol/microgram poly(A)(+) RNA in corpora lutea collected on Day 4 of the estrous cycle and Day 13 of pregnancy, respectively. These data suggest that there is a greater capacity to synthesize PGF(2alpha), early in the estrous cycle and early in pregnancy than on Day 13 of the estrous cycle. In conclusion, enzymatic activity of PGDH may play an important role in the mechanism involved in luteal resistance to the luteolytic effects of PGF(2alpha).

Mutations in an oocyte-derived growth factor gene (BMP15) cause increased ovulation rate and infertility in a dosage-sensitive manner

Multiple ovulations are uncommon in humans, cattle and many breeds of sheep. Pituitary gonadotrophins and as yet unidentified ovarian factors precisely regulate follicular development so that, normally, only one follicle is selected to ovulate. The Inverdale (FecXI) sheep, however, carries a naturally occurring X-linked mutation that causes increased ovulation rate and twin and triplet births in heterozygotes (FecXI/FecX+; ref. 1), but primary ovarian failure in homozygotes (FecXI/FecXI; ref. 2). Germ-cell development, formation of the follicle and the earliest stages of follicular growth are normal in FecXI/FecXI sheep, but follicular development beyond the primary stage is impaired. A second family unrelated to the Inverdale sheep also has the same X-linked phenotype (Hanna, FecXH). Crossing FecXI with FecXH animals produces FecXI/FecXH infertile females phenotypically indistinguishable from FecXI/FecXI females. We report here that the FecXI locus maps to an orthologous chromosomal region syntenic to human Xp11.2-11.4, which contains BMP15, encoding bone morphogenetic protein 15 (also known as growth differentiation factor 9B (GDF9B)). Whereas BMP15 is a member of the transforming growth factor beta (TGFbeta) superfamily and is specifically expressed in oocytes, its function is unknown. We show that independent germline point mutations exist in FecXI and FecXH carriers. These findings establish that BMP15 is essential for female fertility and that natural mutations in an ovary-derived factor can cause both increased ovulation rate and infertility phenotypes in a dosage-sensitive manner.

Gene expression in abnormal ovarian structures of ewes homozygous for the inverdale prolificacy gene

Animals heterozygous (I+) for the Inverdale prolificacy gene (FecX(I)) have an increased ovulation rate whereas those homozygous (II) for FecX(I) are infertile with "streak" ovaries and follicular development arrested at the primary (type 2 follicle) stage. The streak ovaries also contain small oocyte-free nodules with granulosa-like cells and often tumor-like structures. It has been hypothesized that these abnormal structures are of granulosa cell origin, and the aim of this study was to determine whether genes normally expressed in granulosa cells are also expressed in the nodules and tumor-like structures. The mRNAs encoding c-kit and its ligand stem cell factor (SCF), FSH receptor (FSH-R), follistatin, alpha-inhibin subunit, and the beta(A)- and beta(B)-activin/inhibin subunits were localized in ovaries of ewes with 0 (++), 1 (I+), or 2 (II) copies of the FecX(I) gene (n = 4-9 animals per genotype per gene) using in situ hybridization. Ontogeny of expression of all mRNAs examined was similar between ++ and I+ ewes. Expression of c-kit mRNA was observed in the oocyte of all follicular types present in ++, I+, and II ewes. Moreover, granulosa cells of type 2 (II) and type 2 and larger follicles (++, I+) expressed SCF mRNA. The mRNAs encoding FSH-R, follistatin, alpha-inhibin subunit, and beta(B)-activin/inhibin subunit were identified in type 3 and larger follicles of ++ and I+ ewes but not in follicles of II ewes that were only at the type 1, 1a, or 2 stages of development. However, the cells within the oocyte-free nodules of II ewes expressed all of these genes. The mRNAs encoding c-kit and beta(A)-activin/inhibin subunit were not observed in granulosa cells until antrum formation (type 5 follicles) or in the nodules of II ewes. Tumors from 4 ewes were obtained and classified as cystic, semisolid, or solid structures containing granulosa-like cells or as solid structures containing predominately fibroblast- and luteal-like cells. Often, two tumors were present on the same ovary. Tumors containing granulosa-like cells (n = 3-4 per gene) expressed the mRNAs encoding alpha-inhibin subunit, beta(A)-, and beta(B)-activin/inhibin subunits, follistatin, and the FSH-R but did not contain detectable amounts of mRNA for c-kit or SCF. Tumors composed predominately of fibroblast- and luteal-like cells expressed very low levels of SCF mRNA; of the other mRNAs examined, none were detected. Also, none of the genes examined were found to be expressed by the surface epithelium, theca externa, fibroblast, or vascular cells within the ovary of animals of any genotype. These findings are consistent with the hypothesis that the somatic cells in oocyte-free nodules and tumor-like tissue in II ewes originate from the granulosa cells of the small follicles.

Growth and paracrine factors regulating follicular formation and cellular function

The purpose of this paper is to review, using fetal sheep as the animal model, aspects of ovarian development related to follicular formation and to report on the identity of growth and paracrine factors which might be involved in this process. Before follicular formation there is a massive and sustained colonisation of the fetal ovary by mesonephric cells, which become a precursor source of follicular cells. From within the ovarian medulla, somatic 'cell-streams' branch into the cortex around nests of oogonia and oocytes. These 'cell-streams', which contain elongated cells with either flattened or cuboidal shaped nuclei, express steroidogenic factor-1 (SF-1), steroid acute regulatory protein (StAR), 3beta-hydroxysteroid dehydrogenase (3beta-HSD), cytochrome P450(scc), and P450(aromatase) mRNA and/or protein. Follicles form from the association of an oocyte with the 'cell-stream' with either a single layer of flattened cells (i.e. type 1 follicle) or with a mixture of flattened and cuboidal cells (i.e. type 1a follicle). These newly-formed follicles have between 3 and 57 somatic cells (i.e. granulosa cells) and contain oocytes which vary in diameter between 23 and 52 microm. Newly formed and early growing follicles have been identified with growth factors or growth factor receptors in either the oocytes or granulosa cells. Many of the growth factors are from the TGFbeta superfamily and are expressed in a cell- and stage-specific manner.

Effect of dose of prostaglandin F(2alpha) on steroidogenic components and oligonucleosomes in ovine luteal tissue

To determine whether prostaglandin (PG) F(2alpha) had a dose-dependent effect upon secretion of progesterone, oligonucleosome formation, or loss of luteal weight, ewes on Day 9 or 10 of the estrous cycle were administered 0, 3, 10, or 30 mg PGF(2alpha) per 60 kg BW (i.v.), and luteal tissue was collected 9 and 24 h after injection. All doses of PGF(2alpha) decreased (P < 0. 05) concentrations of progesterone in sera by 9 h; however, in ewes treated with 3 mg PGF(2alpha), concentrations of progesterone were similar to control values at 24 h and higher (P < 0.05) than those in the 10- or 30-mg groups. Concentrations of progesterone in sera over all dose levels were highly correlated to luteal concentrations of mRNA encoding steroidogenic acute regulatory protein (P < 0.001), cytochrome P450 side-chain cleavage (P < 0.02), and 3beta-hydroxysteroid dehydrogenase (P < 0.01). Corpora lutea collected at 24 h from ewes treated with the 10- and 30-mg doses of PGF(2alpha) weighed less (P < 0.05) than those from controls. Oligonucleosomes were not present in luteal tissues from control ewes. Surprisingly, all doses of PGF(2alpha)-induced oligonucleosomes in a majority of animals at 9 h and in a majority of ewes treated with 10 and 30 mg of PGF(2alpha) at 24 h. In conclusion, 3 mg of PGF(2alpha) per 60 kg BW transiently decreased serum concentrations of progesterone and induced oligonucleosome formation, but did not result in reduced luteal weight. The 10- and 30-mg doses of PGF(2alpha) decreased secretion of progesterone and induced oligonucleosome formation and luteolysis.

Molecular regulation of luteal progesterone synthesis in domestic ruminants

Regulation of progesterone secretion from the corpus luteum during the oestrous cycle requires the integration of multiple signals to achieve the appropriate amount of progesterone to maximize reproductive efficiency. Development of a mature corpus luteum capable of secreting sufficient amounts of progesterone is dependent upon the pituitary hormones LH and growth hormone (GH). Continued secretion of progesterone from the mature corpus luteum is also dependent upon pituitary hormones. If pregnancy does not occur, prostaglandin F2 alpha (PGF2 alpha) of uterine origin causes a precipitous decrease in progesterone secretion and demise of the corpus luteum. A major point of regulation of progesterone secretion by both luteotrophic and luteolytic hormones appears to be regulation of transport of cholesterol through the mitochondrial membranes to cytochrome P450scc. It is likely that both luteotrophic and luteolytic hormones regulate steroidogenic acute regulatory protein (StAR), which facilitates transport. Regulation may be occurring through increases or decreases in gene transcription, translation efficiency or post-translational modifications such as phosphorylation. Thus, although synthesis of progesterone is a complex process, both positive and negative regulation of the process appears to occur primarily at a single step (transport of cholesterol to the inner mitochondrial membrane) in the pathway.

Mechanisms controlling the function and life span of the corpus luteum

The primary function of the corpus luteum is secretion of the hormone progesterone, which is required for maintenance of normal pregnancy in mammals. The corpus luteum develops from residual follicular granulosal and thecal cells after ovulation. Luteinizing hormone (LH) from the anterior pituitary is important for normal development and function of the corpus luteum in most mammals, although growth hormone, prolactin, and estradiol also play a role in several species. The mature corpus luteum is composed of at least two steroidogenic cell types based on morphological and biochemical criteria and on the follicular source of origin. Small luteal cells appear to be of thecal cell origin and respond to LH with increased secretion of progesterone. LH directly stimulates the secretion of progesterone from small luteal cells via activation of the protein kinase A second messenger pathway. Large luteal cells are of granulosal cell origin and contain receptors for PGF(2alpha) and appear to mediate the luteolytic actions of this hormone. If pregnancy does not occur, the corpus luteum must regress to allow follicular growth and ovulation and the reproductive cycle begins again. Luteal regression is initiated by PGF(2alpha) of uterine origin in most subprimate species. The role played by PGF(2alpha) in primates remains controversial. In primates, if PGF(2alpha) plays a role in luteolysis, it appears to be of ovarian origin. The antisteroidogenic effects of PGF(2alpha) appear to be mediated by the protein kinase C second messenger pathway, whereas loss of luteal cells appears to follow an influx of calcium, activation of endonucleases, and an apoptotic form of cell death. If the female becomes pregnant, continued secretion of progesterone from the corpus luteum is required to provide an appropriate uterine environment for maintenance of pregnancy. The mechanisms whereby the pregnant uterus signals the corpus luteum that a conceptus is present varies from secretion of a chorionic gonadotropin (primates and equids), to secretion of an antiluteolytic factor (domestic ruminants), and to a neuroendocrine reflex arc that modifies the secretory patterns of hormones from the anterior pituitary (most rodents).

Luteal expression of steroidogenic factor-1 mRNA during the estrous cycle and in response to luteotropic and luteolytic stimuli in ewes

Steroidogenic factor-1 (SF-1) is a transcription factor involved in regulating basal and/or cAMP-induced increases in expression of several components of the steroidogenic pathway, including cytochrome P450 side-chain cleavage (P450scc), steroidogenic acute regulatory protein (StAR), and 3beta-hydroxysteroid dehydrogenase/delta5, delta4 isomerase (3beta-HSD). In experiment 1, on days 3, 6, 9, 12, and 15 of the estrous cycle, steady-state concentrations (fmol/microg poly A+ RNA) of SF-1 mRNA in luteal tissue were 0.09 +/- 0.01, 0.17 +/- 0.01, 0.24 +/- 0.03, 0.30 +/- 0.09, and 0.20 +/- 0.05, respectively (estrus = day 0; n = 4/d). Concentrations of SF-1 mRNA increased (p < 0.05) between days 3 and 12, but were not different among the other days of the estrous cycle. Luteal concentrations of SF-1 mRNA and concentrations of progesterone in sera were highly correlated (p < 0.01; r = 0.72). In experiment 2, ewes on days 11 or 12 of the estrous cycle were injected with 25 mg prostaglandin F2alpha (PGF2alpha) into the jugular vein followed by an injection of 10 mg PGF2alpha i.m. 2 h later. Corpora lutea were collected 4, 12, and 24 h after the first injection of PGF2alpha (n = 4-5 ewes/time). Control luteal tissue was collected from ewes on days 11-13 of the estrous cycle, which had not been injected (n = 4) or had been injected with saline 24 h previously (n = 4). Steady-state concentrations of SF-1 mRNA had decreased (p < 0.05) to 48% of control values by 4 h after injection, and remained low at 12 and 24 h. In experiment 3, ewes on days 9-12 of the estrous cycle were administered PGF2alpha (1 micromol), phorbol 12-myristate 13-acetate (PMA; 2 micromol), luteinizing hormone (LH; 20 microg), forskolin (50 microg), or vehicle (1 mL saline) directly into the ovarian artery. Corpora lutea were collected 0 (noninfused) 4, 12, or 24 h later (n = 3-4 animals/treatment/time) for quantification of SF-1 mRNA. Steady-state concentrations of mRNA encoding SF-1 were not affected by infusion of PGF2alpha or PMA, although concentrations of mRNA encoding StAR and 3beta-HSD were decreased (p < 0.05) by these treatments. Concentrations of mRNA encoding SF-1 were increased (p < 0.05) to 157 and 149% of control values by LH and forskolin, respectively, 12 h following infusion and returned to control values by 24 h following either treatment. In contrast, infusion of LH or forskolin did not change concentrations of mRNA encoding StAR, P450scc, or 3beta-HSD. In summary, during the estrous cycle, the pattern of expression of SF-1 mRNA was similar to the pattern of concentrations of progesterone in serum and expression of mRNA encoding P450scc, but differed from that previously shown for 3beta-HSD and StAR mRNA. The effects of administration of PGF2alpha on concentrations of SF-1 mRNA appeared to be dose-dependent. However, acute effects of PGF2alpha on mRNA encoding 3beta-HSD and StAR were observed when concentrations of mRNA encoding SF-1 were not influenced. In addition, although LH or forskolin increased luteal SF-1 mRNA 12 h following infusion, no increases in mRNA encoding StAR, P450scc, or 3beta-HSD were observed. Thus, during the midluteal phase of the estrous cycle, neither luteotropic nor luteolytic hormones appear to coordinately regulate mRNA encoding SF-1 and mRNA encoding StAR, P450scc, or 3beta-HSD.

Steady-state concentrations of mRNA encoding two inhibitors of protein kinase C in ovine luteal tissue

Prostaglandin F2 alpha (PGF2 alpha) decreases secretion of progesterone from the corpus luteum in domestic ruminants. However, it is less effective during the early part of the oestrous cycle (Louis et al., 1973) and at the time of maternal recognition of pregnancy (Silvia and Niswender, 1984; Lacroix and Kann, 1986). Decreased luteal responsiveness may be due to failure of PGF2 alpha to activate fully its normal second messenger system, protein kinase C (PKC). Alternatively, increased resistance of the corpus luteum to PGF2 alpha might be attributable to greater concentrations of recently identified biological inhibitors of PKC. These possibilities were addressed by measuring steady-state concentrations of mRNA encoding PGF2 alpha receptor and two inhibitors of PKC, protein kinase C inhibitor-1 (PKCI-1) and kinase C inhibitor protein-1 (KCIP-1, brain 14-3-3 protein), in corpora lutea collected from ewes on days 4, 10 and 15 of the oestrous cycle (n = 5 per day) and day 15 of pregnancy (n = 7). There were no differences in mean concentrations of mRNA encoding PGF2 alpha receptor among the groups. However, concentrations of mRNA encoding both inhibitors of PKC were higher (P < 0.01) on day 4 of the oestrous cycle compared with the other groups. Treatment of ewes with a luteolytic dose of PGF2 alpha, which activates PKC, did not change concentrations of mRNA encoding either PKCI-1 or KCIP-I up to 24 h later. Luteal expression of mRNA encoding the PKC inhibitors and PGF2 alpha receptor was also examined in ewes treated with oestradiol in vivo for 16 h in the midluteal phase. High concentrations of oestradiol in serum (20 and 70 pg ml-1) did not influence quantities of any of the mRNAs examined. Therefore, an increase in PKC inhibitors may be involved in resistance of the corpus luteum to PGF2 alpha during the early part of the oestrous cycle but does not appear to mediate the increased resistance of the corpus luteum to PGF2 alpha during maternal recognition of pregnancy. Neither PGF2 alpha nor oestradiol affected steady-state concentrations of mRNAs encoding PKCI-1 or KCIP-I.

Concentration of mRNA encoding 3 beta-hydroxysteroid dehydrogenase/delta 5,delta 4 isomerase (3 beta-HSD) and 3 beta-HSD enzyme activity following treatment of ewes with prostaglandin F2 alpha

The objectives of these experiments were (1) to determine if prostaglandin F2 alpha (PGF2 alpha) decreased mRNA encoding 3 beta-hydroxysteroid dehydrogenase/d5,delta 4 isomerase (3 beta-HSD) specifically in large steroidogenic luteal cells, which contain the high affinity receptors for PGF2 alpha; and (2) to determine if the decreased concentration of mRNA encoding 3 beta-HSD following administration of PGF2 alpha was associated with a decrease in 3 beta-HSD enzyme activity. Ewes on days 11 or 12 of the estrous cycle were administered PGF2 alpha (25 mg i.v. followed by 10 mg i.m. 2 h later) and corpora lutea collected 4, 12, 24, or 48 h later (n = 4-5/time). Corpora lutea were also collected from non-injected (n = 4) or saline-injected (n = 4) control ewes. Administration of PGF2 decreased (P < 0.05) steady-state concentrations of mRNA encoding 3 beta-HSD to 35, 15, 9, and 5 percent of the concentrations in the control group at 4, 12, 24, and 48 h, respectively. Concentrations of mRNA encoding 3 beta-HSD in large luteal cells were decreased to 43% of controls 4 h following injection, which was similar to the decrease seen in steady-state concentrations of this mRNA in total luteal mRNA (35%). However, 3 beta-HSD enzyme activity was not significantly decreased by 48 h after PGF2 alpha injection. Thus, the dramatic decreased in mRNA encoding 3 beta-HSD was not associated with an immediate decrease in 3 beta-HSD enzyme activity and, therefore, does not appear to be responsible for the acute decrease in secretion of progesterone from ovine luteal tissue during PGF2 alpha-induced luteolysis.

Hormonal regulation of monocyte chemoattractant protein-1 messenger ribonucleic acid expression in corpora lutea

Monocyte chemoattractant protein-1 (MCP-1) is a potent chemokine that attracts monocytes and macrophages. It is known that macrophages accumulate in the corpus luteum (CL) during luteal regression in many species. In this study, we investigated the regulation of MCP-1 mRNA in ovine and bovine CL during prostaglandin (PG) F2alpha-induced luteolysis, after LH treatment, or after pharmacologic activation of the protein kinase (PK) A or PKC intracellular effector systems. In experiment 1, ewes on day 11 or 12 of the estrous cycle were infused with saline or PGF2alpha. PGF2alpha increased MCP-1 mRNA at 1 and 4 h after treatment. MCP-1 mRNA returned to basal level at 12 h and increased again at 24 h post treatment. In experiment 2, ewes received saline, PGF2alpha, phorbol 12-myristate 13-acetate (PMA), luteinizing hormone (LH), or forskolin infusion and CL were collected at 0 (untreated), 4, 12, or 24 h after infusion. Similar to experiment 1, PGF2alpha induced MCP-1 mRNA at 4 and 24 h post treatment. PMA increased mRNA for MCP-1 at 4, 12, and 24 h. Treatment with LH or forskolin transiently decreased MCP-1 mRNA expression. In experiment 3, cows were treated with a luteolytic dose (25 mg) of PGF2alpha on day 4 or day 11 of estrous cycle and expression of MCP-1 mRNA was quantified. Steady-state concentrations of mRNA for MCP-1 were induced by PGF2alpha treatment only in mid-cycle CL but not in early CL. In summary, administration of PGF2alpha or activation of PKC induced MCP-1 mRNA expression. Expression of MCP-1 may be important for stimulating immune processes during luteal regression.

Effects of luteotrophic and luteolytic hormones on expression of mRNA encoding insulin-like growth factor I and growth hormone receptor in the ovine corpus luteum

The regulation of mRNAs encoding insulin-like growth factor I (IGF-I) and the receptor for growth hormone (GH-R) in ovine luteal tissue by luteotrophic and luteolytic hormones was examined. In Expt 1, ewes were hypophysectomized (HPX) on day 5 of the oestrous cycle and administered saline (S), LH, GH, or LH + GH until day 12 of the oestrous cycle (n = 4 ewes per group). Concentrations of luteal mRNA encoding IGF-I in HPX + S ewes and pituitary-intact ewes at day 5 (n = 4) were approximately 60% (P < 0.05) of those in pituitary-intact ewes at day 12 (n = 4). Treatment of HPX ewes with GH or GH + LH, but not LH alone, increased concentrations of mRNA encoding IGF-I to values similar to those in pituitary-intact ewes at day 12. Hypophysectomy also reduced the mean concentration of mRNA encoding GH-R to approximately 60% (P < 0.05) of the values in pituitary-intact ewes (days 5 or 12). Treatment with LH, but not GH, increased (P < 0.05) concentrations of mRNA encoding GH-R to values observed in pituitary-intact ewes. In Expt 2, prostaglandin F2 alpha (PGF2 alpha; 1 mumole) injected into the ovarian artery on day 11 or day 12 of the oestrous cycle had no effect on luteal concentrations of mRNA for either IGF-I or GH-R. In Expt 3, concentrations of mRNA encoding IGF-I increased (P < 0.05) between days 3 and 6 and remained high for the duration (days 9, 12 and 15) of the oestrous cycle while luteal concentrations of mRNA encoding GH-R did not change. In conclusion, responsiveness of the corpus luteum to GH and luteal synthesis of IGF-I are likely regulators of luteal development and function. However, PGF2 alpha-induced luteolysis was not associated with a decrease in concentrations of mRNAs encoding either IGF-I or GH-R.

Effects of ovariectomy and hypothalamic-pituitary disconnection on amounts of steroidogenic factor-1 mRNA in the ovine anterior pituitary gland

Steroidogenic factor-1 (SF-1) is a transcription factor involved in regulation of steroidogenic enzymes. Recent evidence indicates that SF-1 is also important in the anterior pituitary gland, where it may influence gene expression in gonadotropes. We isolated a cDNA encoding ovine SF-1 and demonstrated that the SF-1 gene is expressed in the anterior pituitary gland of sheep. SF-1 transcripts and luteinizing hormone (LH) were colocalized in gonadotropes by in situ hybridization and immunohistochemistry, respectively. To test the hypothesis that GnRH stimulates pituitary expression of ovine SF-1 mRNA, ewes were ovariectomized to increase endogenous secretion of GnRH. Compared to ovary-intact ewes, ovariectomy resulted in three- and fourfold increases in steady-state amounts of mRNA encoding SF-1 and LH beta subunit, respectively. In ovariectomized ewes in which delivery of GnRH to the anterior pituitary gland was prevented by hypothalamic-pituitary disconnection (HPD), steady-state amounts of mRNA encoding SF-1 and LH beta-subunit were decreased. These results provide evidence that pituitary SF-1 gene expression in sheep is regulated by GnRH. Coordinate regulation of mRNAs encoding SF-1 and LH beta-subunit raises the possibility that SF-1 may be an important transcriptional regulator of LH beta-subunit gene expression in ovine gonadotropes.

Regulation of steady-state concentrations of messenger ribonucleic acid encoding prostaglandin F2 alpha receptor in ovine corpus luteum

To investigate the regulation of ovine luteal receptors for prostaglandin F2 alpha (PGF2 alpha), reverse transcription-polymerase chain reaction was used to produce a 284-bp partial cDNA that was 98% identical to that reported for the bovine PGF2 alpha receptor (PGF2 alpha-R). In situ hybridization localized mRNA for PGF2 alpha-R specifically to large luteal cells. In experiment 1, pools of luteal tissue (n = 4/day) collected from ewes on Days 3, 6, 9, 12, and 15 of the estrous cycle were analyzed for mRNA encoding PGF2 alpha-R. There was no difference in mean steady-state concentrations of mRNA encoding PGF2 alpha-R among any of the days studied (range = 2.3 +/- 0.3 to 3.5 +/- 0.7 fmol PGF2 alpha-R mRNA/ microgram poly[A]+ RNA as assessed by slot-blot hybridization). In experiment 2, ewes on Day 11 or Day 12 of the estrous cycle were administered PGF2 alpha, and corpora lutea were collected 4, 12, or 24 h later (n = 4-5 per time point). Nontreated (n = 4) or saline-treated (n = 4) ewes served as controls. Luteal concentrations of mRNA encoding PGF2 alpha-R were decreased (p < 0.05) at 4, 12, and 24 h after injection of PGF2 alpha. In experiment 3, ewes (midluteal phase) were administered saline, PGF2 alpha, phorbol 12-myristate 13-acetate (PMA), or LH via ovarian arterial injection, and luteal tissue was collected 0, 4, 12, or 24 h later (n = 3-4 per treatment per time). Steady-state concentrations of mRNA encoding PGF2 alpha-R were decreased (p < 0.05) by PGF2 alpha and PMA treatment (4 and 12 h) but were increased (p < 0.05) at 24 h after LH treatment. In summary, 1) mRNA encoding PGF2 alpha-R was localized to large luteal cells; 2) concentrations of mRNA encoding PGF2 alpha-R did not vary during the estrous cycle; 3) treatment with PGF2 alpha or PMA to activate protein kinase C decreased concentrations of PGF2 alpha-R mRNA within 4 h of treatment; and 4) administration LH increased concentrations of mRNA encoding PGF2 alpha-R 24 h following injection.

Ontogenies of messenger RNA encoding tissue inhibitor of metalloproteinases 1 and 2 within bovine periovulatory follicles and luteal tissue

Tissue inhibitors of metalloproteinases 1 and 2 (TIMP-1 and TIMP-2) are important regulators of extracellular matrix remodeling and also possess growth factor activity. The objective of these studies was to characterize TIMP-1 and TIMP-2 mRNA expression by bovine periovulatory follicles/ corpora hemorrhagica (Experiment 1) and luteal tissue (Experiment 2). In Experiment 1, beef heifers (n = 27) were ovariectomized at-16 (n = 6), 0 (n = 5), 8 (n = 3), 16 (n = 4), 24 (n = 4), or 48 (n = 5) hr relative to a gonadotropin-releasing hormone induced gonadotropin surge (40 hr after prostaglandin F2 alpha-induced luteolysis). Total cellular RNA was isolated from the large steroidogenically active follicle or corpus hemorrhagicum obtained from each animal, and the expression of TIMP-1 and TIMP-2 mRNA was subsequently examined by northern and dot blot analysis. The expression of TIMP-1 or TIMP-2 mRNa did not differ in preovulatory follicles collected at -16 vs. 0 hr. Concentrations of both TIMP-1 and TIMP-2 mRNA (picograms per microgram of tissue DNA) were increased (P < 0.05) at 8 hr postgonadotropin surge, had declined to presurge levels by 24 hr (P < 0.05), and were increased (P < 0.05) in corpora hemorrhagica collected at 48 hr after a gonadotropin surge. In Experiment 2, corpora lutea were collected from beef heifers on Days 4, 10, 15 (n = 4 each), or 19 (n = 3) postestrus (Day 0 = estrus). Concentrations of TIMP-1 mRNA (picograms per microgram of tissue DNA) were greater in corpora lutea collected on Day 4 (P < 0.05) vs. Day 10, 15, or 19. Concentrations of TIMP-2 mRNA increased (P < 0.05) from Day 4 to 15 and decreased (P < 0.05) by Day 19. We conclude that: 1) during the periovulatory period, the ontogenies of TIMP-1 and TIMP-2 mRNA expression are similar, whereas 2) during luteal phase, TIMP-1 mRNA expression is maximal during the early luteal phase, whereas concentrations of TIMP-2 mRNA peak during the midluteal phase. TIMP-1 and TIMP-2 may play important roles in the regulation of extracellular matrix remodeling during the periovulatory period and the subsequent luteal phase.

Regulation of mRNA encoding low density lipoprotein receptor and high density lipoprotein-binding protein in ovine corpora lutea

Three experiments were conducted to examine the regulation of steady-state concentrations of mRNA encoding ovine low density lipoprotein receptor (LDL-R) and high density lipoprotein-binding protein (HBP) in corpora lutea. In Experiment 1, corpora lutea were collected from ewes on Days 3, 6, 9, 12 and 15 (Day 0, oestrus) of the oestrous cycle. Enriched preparations of small and large steroidogenic luteal cells were also obtained on Days 6, 9, 12 and 15 of the oestrous cycle. In Experiment 2, 16 ewes were hypophysectomized on Day 5 of the oestrous cycle and received saline, luteinizing hormone (LH), growth hormone (GH) or a combination of LH+GH until collection of luteal tissue on Day 12 of the oestrous cycle. Corpora lutea were also collected from pituitary-intact control ewes on Day 5 and Day 12 of the oestrous cycle. In Experiment 3, 13 ewes on Day 11 or Day 12 of the oestrous cycle were administered prostaglandin F2 alpha (PGF2 alpha) and corpora lutea were collected 4 h, 12 h and 24 h later. Corpora lutea were also collected from 4 non-injected and 4 saline-injected (at 24 h) ewes. Results demonstrated that concentrations of mRNA encoding LDL-R did not differ throughout the oestrous cycle. Luteal tissue collected on Day 3 of the oestrous cycle had higher concentrations of mRNA encoding HBP than luteal tissue collected on any other day of the oestrous cycle. Hypophysectomy increased concentrations of mRNA encoding LDL-R but had no effect on concentrations of mRNA encoding HBP. Twelve hours following PGF2 alpha injection concentrations of mRNA encoding LDL-R were decreased but concentrations of mRNA encoding HBP were increased. Concentrations of both LDL-R and HBP mRNA were decreased 24 h following injection of PGF2 alpha. Thus, long-term positive and acute negative regulation of progesterone secretion from the corpus luteum by luteotrophic and luteolytic hormones was not mediated by changes in steady-state concentrations of mRNA encoding LDL-R or HBP.

Hormonal regulation of messenger ribonucleic acid encoding steroidogenic acute regulatory protein in ovine corpora lutea

Steroidogenic acute regulatory protein (StAR), proposed to be involved in the transport of cholesterol to the inner mitochondrial membrane, has recently been cloned from MA-10 cells. Using reverse transcription-polymerase chain reaction, we generated a complementary DNA encoding 404 base pairs of StAR from ovine luteal tissue to perform studies regarding regulation of the messenger RNA (mRNA) encoding this protein. In Exp 1, ewes were hypophysectomized (HPX) on day 5 of the estrous cycle and administered saline or physiological regimens of LH and/or GH until collection of luteal tissue on day 12 of the estrous cycle (n = 4/group). Luteal concentrations [mean +/- SEM; femtomoles per microgram poly(A)+ RNA] of mRNA encoding StAR were lower (P < 0.05) in the HPX plus saline-treated ewes (26.4 +/- 7.3) than in day 12 pituitary-intact ewes (n = 4; 77.7 +/- 9.3). Replacement of LH (59.1 +/- 13.1), GH (59.1 +/- 12.8), or LH and GH (69.9 +/- 4.5) in HPX ewes increased (P < 0.05) concentrations of mRNA encoding StAR to values not different from those in day 12 controls. In Exp 2, ewes on day 11 or 12 of the estrous cycle were injected with prostaglandin F2 alpha (PGF2 alpha) to induce luteal regression. Corpora lutea were collected 4, 12, or 24 h after injection (n = 4-5/time point) and from untreated control ewes (n = 4) or 24 h after injection of saline (n = 4). Treatment with PGF2 alpha decreased (P < 0.05) concentrations of progesterone in serum 4, 12, and 24 h after injection. Concentrations of StAR mRNA were decreased (P < 0.01) to 47%, 19%, and 8% of control values 4, 12, and 24 h after PGF2 alpha injection, respectively. In Exp 3, ewes received ovarian arterial infusions of saline, PGF2 alpha, or phorbol 12-myristate 13-acetate (PMA), and luteal tissue was collected 0 (no infusion), 4, 12, or 24 h later (n = 3-4/group). Treatment with PGF2 alpha or PMA decreased (P < 0.05) concentrations of progesterone in serum 4, 12, and 24 h postinjection. Steady state concentrations of mRNA encoding StAR (P < 0.05) were 36% and 25% of the control value 12 and 24 h after PGF2 alpha injection. Injection of PMA decreased (P < 0.05) concentrations of StAR mRNA to 75% and 50% of control values at 4 and 12 h, but concentrations of mRNA encoding StAR were not different from control values at 24 h.(ABSTRACT TRUNCATED AT 400 WORDS)

Steady-state concentrations of mRNA encoding the receptor for luteinizing hormone during the estrous cycle and following prostaglandin F(2α) treatment of ewes

A partial cDNA was used to measure steady-state concentrations of mRNA encoding the receptor for luteinizing hormone (LH) in ovine corpora lutea. In experiment 1, luteal tissue and purified preparations of small and large steroidogenic luteal cells (n=4 per day) were obtained on days 3 (tissue only), 6, 9, 12 and 15 of the estrous cycle (estrus=day 0). Steady-state concentrations (fmoles receptor mRNA/μg poly(A)(+) RNA) and total quantities of mRNA (fmoles/corpus luteum) encoding the receptor for LH in luteal tissue increased (P<0.05) from day 3 to days 9 and 12 of the cycle; values on days 6 and 15 were intermediate. Small luteal cells contained at least four-fold greater (P<0.001) concentrations of mRNA encoding the receptor for LH than large luteal cells on days 6, 9, 12 and 15 of the cycle. In experiment 2, ewes on days 11 or 12 of the cycle received an infusion of either 1 μmol prostaglandin F(2α) (PGF(2α)) or saline into the ovarian artery. Luteal tissue was collected 1 (n=6), 4 (n=5), 12 (n=5) or 24 (n=5) h following PGF(2α) infusion, and 0 (no infusion;n=3), 12 (n=3) or 24 (n=4) h following saline administration. Concentrations of progesterone in sera decreased (P<0.05) within 12 h and remained low, whereas luteal weight and concentrations of progesterone in luteal tissue did not decrease (P<0.05) until 24 h after PGF(2α) treatment. Steady-state concentrations of mRNA encoding the receptor for LH were reduced (P<0.05) within 4 h of PGF(2α) infusion, and continued to decrease at 12 and 24 h post treatment. Calculated amounts of mRNA encoding the receptor for LH per corpus luteum were reduced (P<0.05) at 12 h after the PGF(2α) treatment and were 10% (P<0.05) of the values in saline-treated ewes at 24 h post-treatment. The increase during the estrous cycle in steady-state concentrations of mRNA encoding the receptor for LH appears to occur prior to the previously observed increase in number of receptors for LH. Following PGF(2α)-induced luteal regression, concentrations of mRNA encoding LH receptor decreased prior to the previously reported decrease in LH binding. Thus, changes in the number of receptors for LH in ovine luteal tissue during luteal development and luteolysis appears to be preceded by corresponding changes in mRNA encoding this receptor.

Pulsatile gonadotropin-releasing hormone (GnRH) increases concentrations of GnRH receptor messenger ribonucleic acid and numbers of GnRH receptors during luteolysis in the ewe

As circulating concentrations of progesterone decrease during the early preovulatory period, concentrations of mRNA encoding ovine GnRH receptor in the anterior pituitary gland increase. The purpose of this study was to determine whether removal of progesterone affects amounts of GnRH receptor mRNA directly or whether withdrawal of progesterone affects GnRH receptor gene expression indirectly by permitting secretion of GnRH to increase. Ovulation was induced in seasonally anestrous ewes, and luteolysis was initiated with prostaglandin F2 alpha (PGF2 alpha) 11 or 12 days later. Anterior pituitary glands were collected 0 h, 4 h, 12 h, or 24 h after treatment with PGF2 alpha, and 24 h after injection of saline (n = 3 or 4 animals/group). Two groups of ewes (n = 3) received infusions of GnRH (250 ng infused over 6 min) hourly for 12 h; luteolysis was induced in one of these groups at the time that treatment with GnRH was initiated, and anterior pituitary glands were collected at the end of the 12-h infusion period. Blood samples were collected at 15-min intervals for 12 h from all ewes treated with GnRH and from animals administered PGF2 alpha and killed 12 h later. No differences in concentrations of GnRH receptor mRNA, numbers of GnRH receptors, or circulating concentrations of progesterone or estradiol were detected between groups of animals at 0 h and 24 h after treatment with saline; therefore, data from these control groups were combined. Concentrations of progesterone in serum decreased in PGF2 alpha-treated ewes and were lower (p < 0.05) than those in controls 24 h after treatment with PGF2 alpha.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of luteinizing hormone and growth hormone on luteal development in hypophysectomized ewes

To test the hypothesis that growth hormone (GH) as well as luteinizing hormone (LH) is required for normal luteal growth and function, 16 western range ewes were hypophysectomized (HPX) on day 5 of the estrous cycle. Ewes were randomly assigned to receive saline (S), LH, GH, or LH + GH (n=4 per group) from the time of HPX until collection of corpora lutea 7 days after HPX (day 12). Corpora lutea were also collected from pituitary-intact ewes on days 5 (day 5 control,n=4) and 12 (day 12 control,n=4) of the estrous cycle. To assess luteal function, concentrations of progesterone in sera, luteal weights and luteal concentrations of mRNA encoding cytochrome P450 side-chain cleavage enzyme (P450(scc)) and 3β-hydroxysteroid dehydrogenase/Δ5,Δ4 isomerase (3β-HSD) were determined. Concentrations of progesterone in sera and luteal weights increased between days 5 and 12 of the estrous cycle in control ewes, but not in HPX + S ewes. In HPX ewes treated with LH, concentrations of progesterone in sera and luteal mRNA for P450(scc) and 3β-HSD increased but luteal weights were unaffected. Treatment with GH increased luteal weight and luteal concentrations of mRNA encoding P450(scc) but did not increase concentrations of mRNA encoding 3β-HSD compared to HPX + S ewes. Concentrations of progesterone in sera of GH-treated, HPX ewes were similar to those of day 12 control ewes but not significantly different from those in HPX + S ewes. Treatment of HPX ewes with LH + GH increased all parameters of luteal function measured to values similar to those in day 12 controls. In conclusion, both GH and LH are necessary for normal luteal development in the ewe.

Protein kinase C second messenger system mediates the antisteroidogenic effects of prostaglandin F2 alpha in the ovine corpus luteum in vivo

Experiment I was designed to determine the optimal dose of phorbol 12-myristate 13-acetate (PMA) that inhibited progesterone production when infused into the ovarian artery. The most efficacious dose of PMA was 2 mumol. Experiment II was designed to determine whether activation of protein kinase C (PKC) inhibited progesterone production without initiating luteolysis. Ewes received ovarian arterial infusions of 4 alpha-phorbol (2 mumol, n = 4), PMA (2 mumol, n = 8), or prostaglandin F2 alpha (PGF2 alpha; 1 mumol, n = 5). Concentrations of progesterone in serum decreased by 3 h in PMA-treated ewes and by 5 h in PGF2 alpha treated ewes (p < 0.05). By 48 h, serum levels of progesterone in PMA-treated ewes had returned to control values; but in PGF2 alpha-treated ewes they remained low for the duration of the experiment. Luteal weights and progesterone contents at 48 h were similar in 4 alpha-phorbol- and PMA-treated ewes but were decreased in PGF2 alpha-treated ewes (p < 0.05). Experiment III was designed to determine whether PGF2 alpha or PKC activation induced oligonucleosome formation or influenced mRNA levels for cytochrome P450sec or 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase (3 beta-HSD). Ewes received treatments as in experiment II, and CL were collected at 3, 12, or 24 h (n = 3-4 per group). Luteal weights were decreased (p < 0.05) and oligonucleosome formation was increased (p < 0.05) in PGF2 alpha-treated ewes compared to controls or to PMA-treated ewes by 12 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Steady-state concentrations of messenger ribonucleic acid encoding cytochrome P450 side-chain cleavage and 3 beta-hydroxysteroid dehydrogenase/delta 5,delta 4 isomerase in ovine corpora lutea during the estrous cycle

The objective of these experiments was to determine the pattern of mRNA expression for cytochrome P450 side-chain cleavage (P450scc) and 3 beta-hydroxysteroid dehydrogenase/delta 5,delta 4 isomerase (3 beta-HSD) during luteinization of the follicle and in ovine luteal tissue on Days 3, 6, 9, 12, and 15 of the estrous cycle. Mean concentration of mRNA for P450scc was not different in follicles collected 4 or 24 h after the onset of estrus but increased (p < 0.05) 3-fold by 48 h (corpus hemorrhagicum). With the methods used, mRNA for 3 beta-HSD was not detected until after ovulation and formation of the corpus hemorrhagicum (48 h after onset of estrus). In luteal tissue, mean concentration of mRNA for P450scc increased from Days 3 to 9 (p < 0.05) and had decreased (p < 0.05) by Day 15. Mean concentration of mRNA for P450scc was higher (p < 0.05) in small luteal cells on Day 9 than on Day 15, with values on Days 6 and 12 being intermediate. In large luteal cells, mean concentrations of P450scc mRNA increased (p < 0.05) between Days 6 and 12 and then decreased (p < 0.05) on Day 15. Mean concentration of mRNA for 3 beta-HSD was not different (p = 0.33) in luteal tissue on any day examined. In small luteal cells, mean concentrations of mRNA for 3 beta-HSD decreased between Days 6 and 15 (p < 0.05) while in large luteal cells, mean concentrations decreased (p < 0.05) between Days 12 and 15.(ABSTRACT TRUNCATED AT 250 WORDS)

Pattern of protein production by bovine corpora lutea during luteolysis and characterization of expression of two major secretory products of regressing corpora lutea

Although the decrease of progesterone in serum and in luteal tissue during luteal regression is well characterized, relatively little is known about changes in proteins produced by the corpus luteum during this time. The first objective was to examine changes in patterns of protein secretion that might be associated with functional and structural luteal regression. The second objective was to characterize the expression of two major secretory products of regressing corpora lutea. Thirty normally cyclic heifers were randomly assigned at day 15-16 of the oestrous cycle (oestrus = day 0) to be ovariectomized at 0 h (no PGF2 alpha; n = 5) or at 4, 8, 12, 24 or 48 h after PGF2 alpha-induced luteal regression (n = 5 per time point). Total cellular RNA was isolated from tissue frozen at the time of ovariectomy. Thin slices (< 1 mm) of tissue were placed in methionine-deficient minimum essential media with [35S]methionine and placed in a humidified CO2 incubator at 38 degrees C. Media and tissues were collected 6 h later. Changes in profiles of secreted proteins were analysed by one-dimensional SDS-PAGE. A number of proteins (relative molecular mass ranging from 14,300 to 200,000) were produced by luteal tissue at each time point (0-48 h). The major secretory proteins had relative molecular masses of approximately 21,500, 28,200, 43,700 and 46,000. Secretion of the relative molecular mass 46,000 protein(s) increased (P < 0.05) between 4 and 24 h after PGF2 alpha injection compared with the 0 h group.(ABSTRACT TRUNCATED AT 250 WORDS)

Luteal function: the estrous cycle and early pregnancy

A number of morphological and biochemical changes occur as the cells of the recently ovulated follicle luteinize and develop into a functional CL. There are two distinct steroidogenic luteal cell types that appear to differentiate from thecal and granulosal cells in the follicle. The control of progesterone secretion is quite different in the two cell types. Prostaglandin F2 alpha (PGF2 alpha) is the primary luteolytic hormone in most mammals. PGF2 alpha appears to exert its antisteroidogenic actions via activation of the protein kinase C system, while its cytotoxic effects appear to be mediated via a dramatic increase in intracellular levels of free calcium. The mechanisms involved in maternal recognition of pregnancy are very diverse between species and may involve direct luteotropic stimulation of the CL, reduced uterine secretion of PGF2 alpha, and/or inhibition of actions of PGF2 alpha at the level of the CL.

Detection of mRNA for inhibin alpha- and beta A-subunits in bovine ovarian tissues and the effect of in vivo administration of GNRH

The aims of these studies were to determine which types of bovine ovarian tissue contain mRNA for inhibin/activin subunits and whether administration of GnRH influences concentration of these mRNAs. In experiment (exp.) one, cows in the luteal phase of the estrous cycle were given prostaglandin F2 alpha (PGF2 alpha) to induce luteal regression and injected after 40 hr with saline (n = 5) or 100 micrograms GnRH (n = 6). Ovaries were removed 6 hr later. In exp. two, unilaterally ovariectomized (OVX) heifers (n = 33) in the luteal phase of their estrous cycle were given PGF2 alpha to induce luteal regression. Twelve heifers were OVX without injection of GnRH at 24 (n = 6) or 40 hr (n = 6) after PGF2 alpha. The remaining heifers (n = 21) were given 100 micrograms GnRH at 40 hr after PGF2 alpha injection and OVX 8 (n = 4), 16 (n = 5), 24 (n = 6) or 48 (n = 6) hr after GnRH injection. Total cellular RNA was isolated from large follicles (exp. one and two), small-medium follicles and stromal tissue (SMS) and corpora lutea (CL; exp. one) tissues and analyzed by dot blot and Northern blot techniques by hybridizing with cDNA probes for human inhibin/activin alpha- and beta A-subunits. Large follicles were classified as steroidogenically active (EA) if follicular fluid (FF) concentration of estradiol-17 beta (E2) was greater than progesterone (P4), or if P4 and E2 concentrations in FF were greater than 100 ng/ml, and estrogen inactive (EI) if FF concentration of E2 and P4 did not satisfy these criteria. In exp. one, mRNA for the alpha-subunit was primarily expressed in EA follicles, and detectable in EI follicles, SMS, and CL while beta A-subunit mRNA was detected only in large EA follicles and a few SMS samples. The mRNA (x +/- SEM fmoles/mg DNA) for both subunits of inhibin/activin was higher (P < .05) in EA follicles from GnRH-treated cows (alpha = 210.2 +/- 38.6; beta A = 376.9 +/- 41.0) than in EA follicles from control cows (alpha = 102.5 +/- 28.6; beta A = 170.8 +/- 57.6). Concentration of mRNA for the alpha-subunit of inhibin in other ovarian tissues was not different (P > .10) between saline and GnRH treatments.(ABSTRACT TRUNCATED AT 400 WORDS)

Apoptosis during luteal regression in cattle

The present studies were conducted to evaluate whether apoptosis occurs during spontaneous and prostaglandin F2 alpha (PGF2 alpha)-induced luteolysis and, if so, to determine the relationship between the onset of luteolysis and oligonucleosome formation (a characteristic of apoptosis). In the first study, nine normally cycling heifers were ovariectomized (ovx) during the midluteal phase (day 10 or 15; day 0 = estrus) or after luteal regression (day 19; n = 3/time point). While there was no evidence of oligonucleosome formation in DNA from corpora lutea (CL) collected on days 10 and 15, each CL collected on day 19 exhibited DNA fragmentation, represented by distinct bands of DNA in approximately 185-basepair multiples. In the second study, heifers were ovx (n = 5; controls) or given 25 mg PGF2 alpha 15-16 days after estrus. Heifers receiving PGF2 alpha were subsequently ovx 4, 8, 12, 24, or 48 h (n = 5/time point) after the injection of PGF2 alpha. The concentration of progesterone in venous sera collected at ovx was not different (P > 0.20) in control and 4 h groups, but was decreased (P < 0.01) in the 8, 12, 24, and 48 h groups. Total CL weight (mean +/- SEM; grams) did not change (P > 0.10) from 0 h (controls) to 24 h after injection (range, 3.2 +/- 0.5 to 4.1 +/- 0.6), but decreased (P < 0.06) to 2.0 +/- 0.3 at 48 h. With ethidium bromide (EtBr) staining, no oligonucleosome formation was detected in CL collected from 0-12 h after PGF2 alpha injection. However, pronounced oligonucleosome formation was observed in all 10 CL collected 24 and 48 h after the injection of PGF2 alpha. The absence of oligonucleosomes in 0 and 4 h samples was confirmed by the more sensitive technique of 3'-end labeling of DNA fragments. Some samples in both the 8 and 12 h groups had slight oligonucleosome formation, while all samples in the 24 and 48 h groups showed evidence of intense oligonucleosome formation. Histological analysis of tissue sections indicated an increase (P < 0.001) in the percentage of degenerated luteal cells in the 24 and 48 h groups compared to that in the 0-12 h groups. These data indicate that apoptosis occurs during both spontaneous and PGF2 alpha-induced luteal regression in cattle; however, apoptosis, as indicated by oligonucleosome formation, is not apparent until after serum progesterone concentrations have begun to decrease.(ABSTRACT TRUNCATED AT 400 WORDS)