Expression of 3beta-hydroxysteroid dehydrogenase, cytochrome p450 17alpha-hydroxylase/17,20-lyase and cytochrome p450 aromatase enzymes in corpora lutea of diestrous and early pregnant mares

Seasonal absence of supplementary corpora lutea in pregnant mares and the relationship with pregnancy loss

Two experiments were conducted in the Northern (UK) and Southern (Brazil) hemispheres to determine the effect of season (month of conception) on the development of supplementary CL (SCL) and the relationship with pregnancy loss. In experiment 1, 199 pregnancies were followed between Day 14 and term, to determine the number of SCL and pregnancy viability (Northern Hemisphere). From the 199 pregnancies, 178 were obtained from inseminations during the breeding season (March-September), while the rest, 21 pregnancies resulted from conceptions in the non-breeding season (October to February). Pregnancies conceived in the breeding season were more likely (P < 0.01) to have at least 1 SCL (75.8 %, 135/178) than pregnancies from the non-breeding season (33 %, 7/21). However, the pregnancy loss between Days 35 and 120 of pregnancy in mares with no SCL was similar (3.5 %, 2/57; P >0.1) than from mares with SCL (1.4 %, 2/142). In Experiment 2 (Southern Hemisphere), three groups of recipients were used based on their ovarian activity at the time of embryo transfer: Anestrus (n = 8), transitional (n = 7) and cyclic (n = 7) recipient mares. While all transitional and cyclic mares developed at least 1 SCL, only 50 % of anestrous recipients (4/8) developed SCL by 120 of gestation. In conclusion, the development of SCL in pregnant mares is influenced by the time of season of conception, therefore it appears to be regulated by the photoperiod and the endogenous seasonal variation in gonadotropin concentrations. Mares with no SCL were not at increased risk of pregnancy loss.

Pregnancy monitoring in mares: Ultrasonographic and endocrine approaches

Methods to diagnose and monitor equine pregnancy continue to advance with improved instrumentation enabling the development of novel, non-invasive approaches to assess fetal well-being and viability using ultrasound and endocrine testing. From early embryonic loss to placentitis, that is typically encountered later in gestation, fetal viability and development as well as placental function can be evaluated using two fundamentally different, structural and functional, approaches. Ultrasound provides structural information on embryonic and fetal growth using such parameters as combined thickness of the uterus and placenta (CTUP), visual assessment of fetal fluids, activity, heart rate and multiple biometrics involving the fetal head and eyes, limbs and joints among many others, depending on the stage of gestation. Endocrine profiles that include progesterone and 5α-dihydroprogesterone, other metabolites, androgens and estrogens can be evaluated simultaneously using liquid chromatography-tandem mass spectrometry (LC-MS/MS) providing more functional information on fetal and placental competence and development. Endocrine information can be used in making clinical decisions including the need for progestin supplementation or when it can cease, and even estimating gestational stage in mares that cannot be easily palpated or scanned, as with mini-breeds or rancorous animals most notably. When used together, monitoring gestation by ultrasound and hormonal analysis provides unusual insight into feto-placental well-being and the progress of pregnancy, helping to identify problems needing therapeutic intervention.

Reproductive performance is associated with seasonal plasma reproductive hormone levels, steroidogenic enzymes and sex hormone receptor expression levels in cultured Asian yellow pond turtles (Mauremys mutica)

In order to understand the endocrine mechanism associated with fecundity of seasonally breeding animals, we investigated the plasma reproductive hormones levels and detected the differences in steroidogenic enzymes and sex hormone receptor mRNA levels in female Mauremys mutica. These turtles were divided into higher fecundity (HF) group than those in lower fecundity (LF) group based on paternity identification in our previous research. The plasma estrogen (E2), testosterone (T) and progesterone (P4) levels were significantly higher in pre-breeding season (PBS) than those in non-breeding season (NBS) and were markedly higher in the HF group than those in LF group. In the hypothalamus, there was significantly higher mRNA abundance of P450-cholesterol side-chain cleavage enzyme (P450Scc) encoded by Cyp11α1, aromatase (Cyp19α1) and 5-reductase (5α-R), but significantly lower mRNA levels of follicular stimulating hormone receptor (FSHR) and progesterone receptor (PR) detected in PBS than those in NBS. The pituitary steroidogenic acute regulatory protein (StAR), cytochrome P450-17alpha-hydroxylase (Cyp17α1), 3-hydroxy-steroid dehydrogenase (3βHSD), 17-hydroxy-steroid dehydrogenase 3 (17βHSD3), Cyp19α1, 5α-R, FSHR, estrogen receptor 1 (ESR1), androgen receptor (AR) and PR transcriptional levels in HF group were up-regulated significantly compared with the LF group. In the ovary, Cyp17α1 and 17βHSD3 transcriptional levels were markedly higher in PBS than those in NBS. We detected significantly increased expression levels of all steroidogenic enzymes, but notably lower mRNA levels of FSHR and PR in uterus during the PBS, and the HF group has significantly higher expression levels of StAR, Cyp17α1, 5α-R and AR than LF group. Our work reveals seasonal variations in hormone regulation as well as gene regulation in turtles, providing reliable information to understand the mechanisms underlying the different reproductive capacity of reptiles.

Testosterone, androstenedione and dehydroepiandrosterone concentrations in pregnant Spanish Purebred mare

Androgens modulate maternal ovarian activity, embryo implantation and correct placental development. The objective of this study was to establish reference values for testosterone (T), androstenedione (A₄) and dehydroepiandrosterone (DHEA) concentrations in pregnant mares. A total of 30 healthy Spanish Purebred mares with an age range of 9.33 ± 3.31 years, were studied during the 11 months of gestation. T, A₄ and DHEA concentrations were determined using EIA validated specifically for equines. T increased in the 2nd and 3rd month (P < 0.05), showing a plateau between the 4th and 6th month, decreased from the 7th to the 9th month (P < 0.05) and increased in the 10th month (P < 0.05), reaching the maximum value in the last month of pregnancy (P < 0.05). A₄ increased in the 2nd month (P < 0.05), reaching the maximum value in the 3rd month (P < 0.05), decreased in the 4th month, increasing in the 5th and 6th month (P < 0.05). From the 7th month the average values decreased until reaching the minimum at the end of gestation. DHEA progressively increased from the 1st to the 5th month, at which time the maximum mean value was reached (P < 0.05), after a decrease in the 6th and 7th month occurred (P < 0.05), reaching the minimum value in the last month of gestation. T, A₄ and DHEA were positive and significantly correlated (P < 0.05). The androgens analyzed in this study can be used as predictive markers of pregnancy in the mare.

5α-dihydroprogesterone concentrations and synthesis in non-pregnant mares

In vivo and in vitro evidence indicates that the bioactive, 5α-reduced progesterone metabolite, 5α-dihydroprogesterone (DHP) is synthesized in the placenta, supporting equine pregnancy, but its appearance in early pregnancy argues for other sites of synthesis also. It remains unknown if DHP circulates at relevant concentrations in cyclic mares and, if so, does synthesis involve the non-pregnant uterus? Jugular blood was drawn daily from cyclic mares (n = 5). Additionally, ovariectomized mares (OVX) and geldings were administered progesterone (300 mg) intramuscularly. Blood was drawn before and after treatment. Incubations of whole equine blood and hepatic microsomes with progesterone were also investigated for evidence of DHP synthesis. Sample analysis for progesterone, DHP and other steroids employed validated liquid chromatography-tandem mass spectrometry methods. Progesterone and DHP appeared a day (d) after ovulation in cyclic mares, was increased significantly by d3, peaking from d5 to 10 and decreased from d13 to 17. DHP was 55.5 ± 3.2% of progesterone concentrations throughout the cycle and was highly correlated with it. DHP was detected immediately after progesterone administration to OVX mares and geldings, maintaining a relatively constant ratio with progesterone (47.2 ± 2.9 and 51.2 ± 2.7%, respectively). DHP was barely detectable in whole blood and hepatic microsome incubations. We conclude that DHP is a physiologically relevant progestogen in cyclic, non-pregnant mares, likely stimulating the uterus, and that it is synthesized peripherally from luteal progesterone but not in the liver or blood. The presence of DHP in pregnant perissodactyla as well as proboscidean species suggests horses may be a valuable model for reproductive endocrinology in other exotic taxa.

The dynamic steroid landscape of equine pregnancy mapped by mass spectrometry

Liquid chromatography–tandem mass spectrometry (LC–MS/MS) allowed comprehensive analysis of various steroids detectable in plasma throughout equine gestation. Mares (n=9) were bled serially until they foaled. Certain steroids dominated the profile at different stages of gestation, clearly defining key physiological and developmental transitions. The period (weeks 6–20) coincident with equine chorionic gonadotropic (eCG) stimulation of primary corpora lutea and subsequent formation of secondary luteal structures was defined by increased progesterone, 17OH-progesterone and androstenedione, all Δ4 steroids. The 5α-reduced metabolite of progesterone, dihydroprogesterone (DHP) paralleled progesterone secretion at less than half the concentration until week 12 of gestation when progesterone began to decline but DHP concentrations continued to increase. DHP exceeded progesterone concentrations by week 16, clearly defining the luteo-placental shift in pregnane synthesis from primarily ovarian to primarily placental. The period corresponding to the growth of fetal gonads was defined by increasing dehydroepiandrosterone and pregnenolone (Δ5 steroids) concentrations from week 14, peaking at week 34 and declining to term. Metabolites of DHP (including allopregnanolone) dominated the steroid profile in late gestation, some exceeding DHP by weeks 13 or 14 and near term by almost tenfold. Thus Δ4 steroids dominated during ovarian stimulation by eCG, inversion of the ratio of progesterone: DHP (increasing 5α-pregnanes) marked the luteo-placental shift, Δ5 steroids defined fetal gonadal growth and 5α-reduced metabolites of DHP dominated the steroid profile in mid- to late-gestation. Comprehensive LC–MS/MS steroid analysis provides opportunities to better monitor the physiology and the progress of equine pregnancies, including fetal development.

The effect of short-term nutritional supplementation of ewes with lupin grain (Lupinus luteus) on folliculogenesis, the concentrations of hormones and glucose in plasma and follicular fluid and the follicular levels of P450 aromatase and IRS-1, -2 and -4

An experiment was conducted on 48 ewes during follicular and luteal phases of the oestrous cycle to determine the effect of a 5-day lupin grain supplementation (500 g/day) on folliculogenesis, plasma concentrations of glucose, insulin, FSH and oestradiol-17β (E2), follicular fluid concentrations of glucose, E2, androstenedione and progesterone and the levels of P450aromatase and insulin receptor substrate 1 (IRS-1), -2 and -4 in theca and granulosa cells. Average weight did not differ between lupin-fed and control groups. The numbers of follicles were increased (P<0.05; χ2) in the lupin-fed group. The plasma concentrations of glucose (P<0.05; ANOVA) and insulin (P<0.001; ANOVA) were higher in lupin-fed ewes. The plasma concentrations of FSH were not different but those of E2were decreased (P<0.001) in the lupin-fed group. Both the follicular fluid concentration of E2(P<0.05) and the level of P450aromatase in granulosa cells (P<0.05; ANOVA) were decreased in the lupin-fed group, but only during the follicular phase. The level of P450aromatase in granulosa cells was positively correlated with the concentration of E2in follicular fluid (r=0.820;P<0.001; ANOVA). The levels of IRS-1 and -2 in theca and granulosa cell lysates were increased in the lupin-fed group. These data suggest that insulin has a local role in the control of folliculogenesis and is likely to be a mediator of the effects of dietary energy intake on ovulation rate. We suggest that insulin acting through IRS proteins mediates the reproductive actions of insulin in the follicle and that IRS-1 and -2 are nutritionally regulated mediators of the action of insulin in the follicle.

Cellular localization of androgen synthesis in equine granulosa-theca cell tumors: immunohistochemical expression of 17alpha-hydroxylase/17,20-lyase cytochrome P450

Elevated blood testosterone concentrations, often accompanied by male-typical behaviors, is a common signalment of mares with granulosa-theca cell tumors (GCTCs), but no definitive information exists regarding the cellular differentiation of tumors associated with androgen secretion. This study was conducted to localize and thereby define the cellular expression of 17alpha-hydroxylase/17,20-lyase cytochrome P450 (P450c17), the enzyme most directly responsible for androgen synthesis, in 30 GTCTs and control tissues (gonads and adrenal glands) using immuno-histochemistry (IHC). Immuno-reactivity for P450c17 was evident in approximately half of 30 specimens examined, was most consistent in the interstitial cells surrounding existing or developing cysts, and was less intense in cells within cysts in the smaller proportion of specimens where this was observed. In control tissues, the expression of P450c17 was localized primarily in theca interna of normal ovarian follicles, in theca-lutein cells of some corpora lutea, but not in granulosa-lutein cells. Testicular interstitial cells and islands of adreno-cortical cells located in the adrenal medulla of the adrenal cortex further established the specificity of the antisera used. These data provided the first substantive evidence that polyhedral cells identified previously in GTCTs by histopathology have the potential to synthesize and secrete androgens, similar to theca interna and theca lutein cells in normal equine ovaries.

Effect of hCG Stimulation on Plasma Androstenone Concentrations and Cytochrome b5 Levels in Testicular Tissue

The effect of Human chorionic gonadotropin (hCG) stimulation on the concentrations of free and conjugated androstenone in plasma was studied in 34 crossbred entire male pigs (Landrace x Swedish Yorkshire). Seventeen pigs were treated with hCG 4 days prior to slaughter and the remaining pigs were treated with sterile saline and served as controls. Blood samples were taken prior to hCG or saline injection and on the day before slaughter and analysed for concentrations of free and conjugated androstenone. Testicular tissue samples were taken at slaughter and analysed for the levels of cytochrome b5 (cyb5) protein. Here we have demonstrated for the first time that hCG stimulation causes an increase in the plasma levels of both free and conjugated androstenone. Not all animals responded in the same way to hCG treatment regarding levels of free and conjugated androstenone demonstrating that individual animals can have differences in their capacity to produce free and conjugated androstenone. We suggest that hCG treatment is a good way to determine the potential for androstenone conjugation when androstenone synthesis in the testis is high. The levels of cyb5 protein in the testis were slightly related (r=0.41, p < 0.10) to free androstenone levels in the pigs after hCG administration, although levels of cyb5 protein were not affected by hCG treatment.

Changes in steady-state concentrations of messenger ribonucleic acids in luteal tissue during prostaglandin F2α induced luteolysis in mares

Transvaginal ultrasound-guided luteal biopsy was used to evaluate the effects of prostaglandin (PG)F2alpha on steady-state concentrations of mRNA for specific genes that may be involved in regression of the corpus luteum (CL). Eight days after ovulation (Hour 0), mares (n=8/group) were randomized into three groups: control (no treatment or biopsy), saline+biopsy (saline treatment at Hour 0 and luteal biopsy at Hour 12), or PGF2alpha+biopsy (5mg PGF2alpha at Hour 0 and luteal biopsy at Hour 12). The effects of biopsy on CL were compared between the controls (no biopsy) and saline+biopsy group. At Hour 24 (12h after biopsy) there was a decrease in circulating progesterone in saline group to 56% of pre-biopsy values, indicating an effect of biopsy on luteal function. Mean plasma progesterone concentrations were lower (P<0.001) at Hour 12 in the PG group compared to the other two groups. The relative concentrations of mRNA for different genes in luteal tissue at Hour 12 was quantified by real time PCR. Compared to saline-treated mares, treatment with PGF2alpha increased mRNA for cyclooxygenase-2 (Cox-2, 310%, P<0.006), but decreased mRNA for LH receptor to 44% (P<0.05), steroidogenic acute regulatory protein to 22% (P<0.001), and aromatase to 43% (P<0.1) of controls. There was no difference in mRNA levels for PGF2alpha receptor between PG and saline-treated groups. Results indicated that luteal biopsy alters subsequent luteal function. However, the biopsy approach was effective for collecting CL tissue for demonstrating dynamic changes in steady-state levels of mRNAs during PGF2alpha-induced luteolysis. Increased Cox-2 mRNA concentrations suggested that exogenous PGF2alpha induced the synthesis of intraluteal PGF2alpha. Thus, the findings are consistent with the concept that an intraluteal autocrine loop augments the luteolytic effect of uterine PGF2alpha in mares.

Immunolocalization of steroidogenic enzymes in the corpus luteum and placenta of the Japanese Shiba goat

In this study, we performed immunohistochemistry of cholesterol side-chain cleavage cytochrome P450 (P450scc), 3beta-hydroxysteroid dehydrogenase (3betaHSD), cytochrome 17alpha-hydroxylase P450 (P450c17), and cytochrome P450 aromatase (P450arom) in the corpus luteum and placenta of Shiba goats. The aim was to clarify the steroidogenic capability of the corpus luteum and placenta of Shiba goats. Ovaries containing corpora lutea were obtained from four adult Shiba goats during the luteal phase (day10; n=2) and pregnancy (90 and 120 days of gestation). Placenta was obtained from one Shiba goat on day 120 of gestation. The sections of the ovaries and placentae were immunostained using the avidin-biotin-peroxidase complex method (ABC) with polyclonal antibodies generated against steroidogenic enzymes of mammalian origin. All luteal cells expressed P450scc, 3betaHSD, P450c17 and P450arom. The distribution of P450scc, 3betaHSD, P450c17 and P450arom were not different during the luteal phase and pregnancy. P450arom showed a weak positive staining in late pregnancy (120 days). In addition, immunoreactions for P450c17 and P450arom were observed in syncytiotrophoblast of the placenta of one Shiba goat. These results indicate that, in Shiba goats, corpus luteum is not only an important source of progesterone but also has the ability to synthesize androgen and estrogen during the luteal phase and pregnancy. Also the placenta has the ability to synthesize androgen and estrogen in late pregnancy.

Identification and physical mapping of genes expressed in the corpus luteum in cattle

A representational difference analysis was performed to identify genes expressed in the corpus luteum of cattle. The corpus luteum is an ovarian structure that is essential for the establishment and maintenance of pregnancy. Knowledge of gene expression and function of corpus luteum will be important to improve fertility in humans and domestic animals. Housekeeping genes were removed from the corpus luteum representation (tester) using skeletal muscle as the subtracting agent (driver). A total of 80 clones of the final subtraction product were analysed by sequencing and 11 new bovine gene sequences were identified (pBTCL1-11). The sequences were mapped to segments of 10 different chromosomes using a somatic cell hybrid panel and a radiation hybrid panel. With one exception the locations are in agreement with published comparative maps of cattle and man. Expression in corpus luteum was verified by RT-PCR for all the 11 clones.