Effects of intraovarian infusion of insulin-like growth factor-I on ovarian follicular function in cattle

Natural Ghee Enhances the Biochemical and Immunohistochemical Reproductive Performance of Female Rabbits

The reproductive effects of several dietary fats (margarine, ghee, and olive oil) on female rabbits were studied. For that purpose, 40 mature female rabbits were designed into four groups of ten rabbits each. Group I was given a control diet, Group II received 10% margarine, Group III received 10% ghee, and Group IV received 10% olive oil; after two months, all rabbits were sacrificed. Lipid profile and reproductive hormones levels were assayed in serum besides ovarian antioxidant enzyme and lipid peroxidation. Furthermore, ovarian tissue was examined using hematoxylin−eosin staining and immunohistochemistry of estrogen, follicle-stimulating hormone (FSH), luteinizing hormone (LH) receptor, and caspase 3. Our data revealed that the margarine significantly (p < 0.05) increased lipid profile and malondialdehyde (MDA) level, which decreased in olive oil and ghee compared to the control. In addition, serum FSH and estrogen (estradiol (E2)) were significantly (p < 0.05) decreased in the group treated with margarine. Furthermore, there was a significant decrease in ovarian superoxide dismutase (SOD) and catalase activity in the margarine-treated group. In contrast, SOD and MDA showed a significant (p > 0.05) increase in the olive oil and ghee- treated group compared to the control group. At the same time, there was a significant increase in serum FSH and (estradiol (E2)) in the ghee and olive oil groups, respectively, compared to the control. The margarine feed group showed moderate immunoreaction of estrogen, FSH, LH receptor, and strong caspase 3, while ghee and olive oil showed strong immunoreaction of estrogen, FSH, LH receptor, and mild immunoreaction of caspase 3 in ovarian tissue. Photomicrograph of rabbit ovarian tissue showed vacuolation in small and growing follicles in the margarine group but appeared normal in ghee and the olive oil-treated group. In conclusion, based on these results, olive oil and ghee have a strong capability of enhancing lipid profile, antioxidant status, and female hormonal functions.

Surgical Procedures of the Genital Organs of Cows

Reproductive surgical techniques are considered by practitioners/clinicians of theriogenology to be the most beneficial reproductive management that can be performed to treat conditions of cows that may affect fertility. Conditions affecting the reproductive tract can cause pathologic changes that may result in substantial economic and genetic losses to beef and dairy producers. Some injuries and diseases are amenable to surgical treatment. Surgical restoration of fertility preserves genetic potential and economic productivity. The surgical procedures described in this article are some of the most commonly used to restore fertility in cows with injury or diseases affecting their reproductive tracts.

Nutritional signals and reproduction

There is extensive evidence that nutrition influences reproductive function in various mammalian species (agricultural animals, rodents and human). However, the mechanisms underlying the relationship between nutrition, energy metabolism and reproductive function are poorly understood. This review considers nutrient sensors as a molecular link between food molecules and consequences for female and male fertility. It focuses on the roles and the molecular mechanisms of some of the relevant hormones, such as insulin and adipokines, and of energy substrates (glucose, fatty acids and amino acids), in the gonadotropic axis (central nervous system and gonads). A greater understanding of the interactions between nutrition and fertility is required for both better management of the physiological processes and the development of new molecules to prevent or cure metabolic diseases and their consequences for fertility.

Growth hormone regulation of follicular growth

The somatotropic axis – consisting of growth hormone (GH), the insulin-like growth factors 1 and 2 (IGF1 and IGF2), GH binding protein (GHBP), IGF binding proteins (IGFBPs) 1 to 6, and the cell-surface receptors for GH and the IGFs – has major effects on growth, lactation and reproduction. The primary target tissues for GH are involved in growth and metabolism. The functionality of the somatotropic axis depends in part on the expression of liver GH receptor (GHR), which determines the amount of IGF1 released from the liver in response to GH. The IGF1 acts as a pleiotropic growth factor and also serves as the endocrine negative feedback signal controlling pituitary GH secretion. Growth hormone and IGF1 undergo dynamic changes throughout the life cycle, particularly when animals are either growing, early post partum or lactating. Cells within the reproductive tract can respond directly to GH but to a lesser degree than the primary target tissues. The major impact that GH has on reproduction, therefore, may be secondary to its systemic effects on metabolism (including insulin sensitivity) or secondary to the capacity for GH to control IGF1 secretion. Insulin-like growth factor 1 and IGFBP are also synthesised within the ovary and this local synthesis is a component of the collective IGF1 action on the follicle. Future studies of GH should focus on its direct effects on the follicle as well as its indirect effects mediated by shifts in nutrient metabolism, insulin sensitivity, IGF1 and IGFBP.

The role of IGF1 in the in vivo production of bovine embryos from superovulated donors

IGF1 plays an important role in bovine follicular growth, acquisition of oocyte competence and embryo viability. Current data also indicate a critical role for IGF1 in both the ovarian response and the embryo yield following the superovulatory treatments. IGF1 can have either positive or negative effects on embryo viability which is related to the concentration of IGF1 induced by superovulation treatment. These effects impact either on oocyte competence or directly on the embryo. Concentrations in the physiological range appear to result in the production of higher quality embryos, mainly due to the mitogenic and the anti-apoptotic activities of IGF1. However, high superovulatory responses are associated with decreased embryo viability and a concomitant increase in apoptosis. Studies in mice suggest that this increase in apoptosis is related to the downregulation of the IGF1 receptor in the embryo associated with high IGF1 concentrations. Strategies capable of controlling the IGF1 concentrations could be one approach to improve superovulation responses. A range of possible approaches for research within the IGF system in gonadotrophin-stimulated cattle is discussed in this review, including the possible use of superovulated female cattle as an alternative animal experimental model for research on reproductive disorders in humans associated with abnormal IGF1 concentrations.

Evaluation of the Mechanism of Action of Conjugated Linoleic Acid Isomers on Reproduction in Dairy Cows

The objective of this study was to evaluate the mechanism of action through which conjugated linoleic acid (CLA) beneficially affects reproduction. Lactating Holstein cows (n = 45, 20 +/- 1 DIM) were assigned to 1 of 3 treatments: 70 g/d of Ca salts of tallow (control); 63 g/d of lipid-encapsulated CLA providing 7.1 g/d of cis-9, trans-11 CLA and 2.4 g/d of trans-10, cis-12 CLA (CLA 75:25); or 76 g/d of lipid-encapsulated CLA providing 7.1 g/d each of cis-9, trans-11 and trans-10, cis-12 CLA (CLA 50:50). Supplements were top-dressed for 37 d, milk production and DMI were recorded daily, and blood samples were taken 3 times per week. At 30 +/- 3 DIM, ovulation was synchronized in all cows with a modified Ovsynch protocol, and on d 15 of the cycle cows received an oxytocin injection; blood samples were obtained frequently to measure 13,14 dihydro, 15-keto PGF2alpha. On d 16 of the cycle cows received a PGF2alpha injection and ovarian follicular aspiration was performed 54 h later. Follicular fluid was analyzed for fatty acids, progesterone, and estradiol. Endometrial biopsies were taken before and again near the end of the supplementation period for fatty acid analysis. The CLA resulted in decreased milk fat content of 14.1 and 6.1% at wk 5 of treatment of CLA 50:50 and CLA 75:25, respectively. There were no differences in energy balance or plasma nonesterified fatty acids; however, plasma IGF-I was greater in cows supplemented with CLA 50:50. The CLA isomers were not detectable in endometrial tissue, but cis-9, trans-11 CLA tended to be greater in follicular fluid of supplemented cows. Response to the oxytocin challenge was not different among treatments. Progesterone during the early luteal phase and the estradiol:progesterone ratio in follicular fluid tended to be greater in cows supplemented with CLA 50:50. Overall, these results indicate that short periods of CLA supplementation do not alter uterine secretion of PGF2alpha. The mechanism through which CLA affects reproduction may involve improved ovarian follicular steroidogenesis and increased circulating concentrations of IGF-I.

Follicle selection in cattle and horses: role of intrafollicular factors

The eminent event in follicle selection during a follicular wave in monovular species is diameter deviation, wherein one follicle continues to grow (developing dominant) and other follicles (subordinates) begin to regress. In cattle, the IGF system, oestradiol and LH receptors are involved in the intrafollicular events initiating deviation as indicated by the following: (1) concentrations of free IGF-I and oestradiol in the follicular fluid and number of LH receptors in the follicular wall increase more dramatically in the future dominant follicle than in the future subordinate follicles before the beginning of deviation and (2) ablation of the largest follicle (LF) or injection of recombinant human IGF (rhIGF)-I into the second LF at the expected beginning of deviation increases the concentrations of oestradiol in second LF before the expected beginning of deviation between second LF and third LF. In horses, an increase in free IGF-I, oestradiol, inhibin-A and activin-A is greater in the future dominant follicle than in other follicles before the beginning of deviation. However, free IGF-I is the only one of these four factors needed for the initiation of deviation in horses as indicated by the following: (1) ablation of LF at the expected beginning of deviation increases the concentrations of free IGF-I in second LF before the beginning of deviation between second LF and third LF but does not increase the other factors; (2) injection of rhIGF-I into second LF at the expected beginning of deviation causes second LF to continue to grow and become a codominant follicle and (3) injection of IGF-binding protein-3 into LF at the expected beginning of deviation causes LF to regress and second LF to become dominant. Thus, the dramatic changes in the IGF system in LF compared to other follicles before the beginning of deviation play a crucial role in the events that lead to the beginning of diameter deviation in both cattle and horses. Oestradiol and LH receptors also play a role in cattle. These intrafollicular events prepare the selected follicle for the decreasing availability of FSH and increasing availability of LH. The other follicles of the wave have the same future capability but do not have adequate time to attain a similar preparatory stage.

Insulin-like growth factor-II stimulates steroidogenesis in cultured bovine thecal cells

The objective of the present study was to determine the effects of insulin-like growth factor-II (IGF-II) on luteinizing hormone (LH)-induced progesterone and androstenedione production by bovine thecal cells and compare it to that of insulin and IGF-I. Cells from large (>7.9 mm) bovine follicles were collected and cultured for 2 days in the presence of 10% fetal calf serum. Then cells were cultured for an additional 1 or 2 days in serum-free medium with various doses of recombinant human IGF-II, bovine LH (30 ng/ml), IGF-I, and(or) insulin. Cell numbers were determined at the end of treatments via Coulter counting and used to correct steroid production data. In the presence of LH, 1-day treatment with 3-300 ng/ml of IGF-II had no significant effect on progesterone or androstenedione production, whereas 2-day treatment with 30, 100 and 300 ng/ml of IGF-II increased (P < 0.05) both progesterone and androstenedione production by 2-3-fold. The estimated effective dose of IGF-II stimulating 50% of the maximal steroidogenic response was calculated to be 25 ng/ml. In the absence of LH, 2-day treatment of IGF-I or -II had no effect on thecal androstenedione production but increased (P < 0.05) thecal progesterone production. In the presence of LH, 100 ng/ml of IGF-I increased progesterone and androstenedione production to a greater degree than did 100 ng/ml of IGF-II. Maximal effects of IGF-I and insulin on thecal steroidogenesis were similar and were not additive. Anti-IGF type I receptor antibodies attenuated (P < 0.05) the stimulatory effect of both IGF-I and IGF-II on thecal cell steroidogenesis. Use of radioligand assays demonstrated that specific receptors for (125)I-IGF-II existed in thecal cells with a 25 ng/well of IGF-II causing 50% inhibition of binding. IGF-I cross-reactivity with (125)I-IGF-II receptors averaged 3% whereas cross-reactivity of IGF-II with (125)I-IGF-I receptors averaged 114%. These results indicate that the stimulatory effects of IGF-II on thecal cell steroidogenesis is mediated by IGF type I receptors and thus IGF-II, like IGF-I, may play a significant role in thecal cell steroidogenesis during follicular development.

Improvement of the Developmental Capacity of Oocytes from Prepubertal Cattle by Intraovarian Insulin-Like Growth Factor-I Application1

The developmental potential of oocytes from prepubertal cattle is decreased, compared with those from their adult counterparts. The aim of the present study was to improve the developmental capacity of oocytes from prepubertal cattle by either systemic application of recombinant bovine somatotropin (rbST) or intraovarian injection of insulin-like growth factor-I (IGF-I). Blastocyst yields and the mRNA expression pattern (relative abundance, RA) of three putative marker genes (i.e., glucose transporter-1, Glut-1; eukaryotic translation initiation factor-1A, eIF1A, and upstream binding factor, UBF) were selected as criteria to determine the success of the treatments. At 6-7 mo of age, 30 healthy Holstein calves were randomly assigned to three experimental groups. The first group served as control and received an intraovarian injection of 0.6 ml acetic acid. The second group received a single s.c. injection of 500 mg of rbST. The third group received an intraovarian injection of 6 microg recombinant human IGF-I. During the following 2 wk, follicles were aspirated four times via transvaginal ultrasound-guided technology. All animals were i.m. injected with 60 mg FSH 48 h prior to each aspiration. The treatments were repeated with the same animals at 9-10, 11-12, and 14-15 mo of age. For comparison, five adult cows were each i.m. injected with 100 mg FSH and underwent oocyte retrieval. The proportion of oocytes considered to be developmentally competent was higher in cows than calves (65% vs. 58%, 50%, 52%) for the control, rbST, and IGF-I groups, respectively. The rate of blastocysts was similar in IGF-I-treated calves and cows (28% and 25%) and was higher (P </= 0.05) than in the controls and the rbST group (11% and 16%). The RA for Glut-1 was lower (P </= 0.05) in two- to four- cell embryos from calves, compared with cows. At the 8- to 16- cell stage, Glut-1 RA was similar in IGF-I-treated calves and cows. The RA for eIF1A was higher (P </= 0.05) in 8- to 16-cell embryos derived from cows than those from the control group. Results show that IGF-I intraovarian injection increased blastocyst yields and mRNA expression of Glut-1 and eIF1A to levels found in embryos produced from adult cows. This treatment may at least partially overcome the developmental deficiency of oocytes derived from calves and could be a step forward toward the use of prepubertal animals in breeding programs aimed at shortening the generation interval.

In vivo effects of an intrafollicular injection of insulin-like growth factor 1 on the mechanism of follicle deviation in heifers and mares

In cattle and mares, free insulin-like growth factor 1 (IGF-1) is higher in the future dominant follicle (F1) than in the future largest subordinate follicle (F2) before deviation in diameter or selection is manifested between the two follicles. The effect of IGF-1 on other follicular-fluid factors and on the destiny of F2 were studied in two experiments in each species, using a total of 40 heifers and 42 mares. An injection of IGF-1 was made into F2 at the expected beginning of deviation (heifers, F1 >or= 8.5 mm; mares, F1 >or= 20.0 mm; Hour 0). In heifers, follicular fluid was taken from F2 at Hours 3, 6, 12, or 24; each heifer was sampled only once. In mares, sequential F2 samples were taken from each mare at Hours 0, 6, and 24 or at Hours 12 and 24. Transvaginal ultrasound guidance was used for treatment and sample collection. In heifers, IGF-1 treatment of F2 stimulated the secretion of estradiol (P < 0.05) between Hours 3 and 6 and androstenedione (P < 0.05) between Hours 3 and 12. In F2 of control heifers, estradiol decreased (P < 0.05) and androstenedione did not change significantly. In mares, IGF-1 treatment of F2 did not affect the concentrations of estradiol during the 24-h posttreatment period; androstenedione decreased (P < 0.04) in the IGF-1 group and increased (P < 0.006) in the controls. Compared with control mares, the IGF-1 group had higher (P < 0.04) activin-A at Hours 12 and 24 and higher (P < 0.0006) inhibin-A at Hour 24. After ablating F1 at Hour 24 in mares, F2 became dominant and ovulated in more mares (P < 0.0002) in the IGF-1 group (12/14) than in the control group (2/14). These results are consistent with reported temporal relationships among follicular factors during deviation in both species and indicate that IGF-1 plays a key role in controlling the temporal relationships; however, no indication was found that IGF-1 stimulated estradiol production in mares during the 24 h after treatment.

Mechanism of follicle deviation in monovular farm species

Diameter deviation is a distinctive change in growth rates among the follicles of a wave, heralding the formation of a dominant follicle and subordinate follicles. When the follicles are about 5mm in cattle and 13 mm in horses, the wave-stimulating FSH surge reaches peak concentrations. Follicle and FSH manipulation studies in both species have shown that the declining portion of the surge before the beginning of deviation is a function of multiple growing follicles that require the decreasing FSH. During this time, all follicles of the wave have the potential for future dominance. Deviation begins when the two largest follicles on average are 8.5 and 7.7 mm in cattle and 22.5 and 19.0 mm in horses or about 3 days after the FSH peak in both species. The FSH/follicle relationship is close so that a change in one event soon causes a detectable change in the other. Thus, the difference in diameter between the two largest follicles at the beginning of deviation is compatible with rapid establishment of the destiny of the two follicles before the second-largest follicle can also show dominance. The deviation mechanism is initiated when FSH concentrations are low and the most advanced follicle reaches a specific developmental stage. In cattle, the future dominant follicle develops greater LH-receptor expression than the other follicles about 8 h before the beginning of diameter deviation. Estradiol and free IGF-1 begin to establish higher concentrations in the future dominant follicle than in other follicles and activin-A is transiently elevated in both follicles a few hours before the beginning of diameter deviation. In horses, estradiol, free IGF-1, activin-A, and inhibin-A begin to increase differentially in the future dominant follicle about 1 day before deviation. These changes underlie a greater responsiveness to LH and FSH by the developing dominant follicle than for other follicles, thereby accounting for deviation. Results of in vitro studies, although frequently done in other species, support this conclusion.

Endocrine regulation of ovarian antral follicle development in cattle

Antral follicle growth in cattle occurs in two distinct phases; the first 'slow' growth phase spans the time from antrum acquisition to a size of approximately 3 mm detectable by transrectal ultrasound, and the second 'fast' phase is gondadotrophin-dependent and includes cohort growth, dominant follicle (DF) selection, and DF growth. This review summarises current concepts of the relative roles FSH and LH, ovarian and metabolic hormones play mainly in the second phase of antral follicle growth in animals of different reproductive and nutritional states. It is proposed that differential FSH response may enable one cohort follicle to become selected, and that follicular secretions, particularly inhibin, suppress FSH and thus are responsible for DF selection and dominance. Acute dependence of the DF on LH pulses will determine DF lifespan, and the LH pulse profile can be influenced by metabolic hormones such as leptin, providing one possible link for nutritional state and reproduction. Direct ovarian effects of acute and chronic changes in growth hormone, insulin and insulin-like growth factor (IGF)-I have been described on cohort follicles, DF oestrogen activity and on DF growth. Influences of metabolic hormones on early antral follicles undergoing their first 'slow' growth phase are less well described, yet metabolic hormones appear to enhance growth into the cohort available for FSH-induced emergence, and may influence subsequent developmental competence of oocytes.

Insulin-like growth factor-I and its binding proteins in colostrum compared to measures in serum of Holstein neonates

Colostral insulin-like growth factor-I (IGF-I) may be beneficial in the development of gastrointestinal tracts of bovine neonates. Thus, the purpose of this study was to examine relationships among concentrations of IGF-I and IGF-binding proteins (IGFBP) in colostrum used at two initial feedings and serum concentrations of IGF-I, IGFBP, total protein, gamma glutamyltransferase (GGT), and immunoglobulin G at 0 and 48 h after birth in Holstein neonates. Calves (n = 22) were separated from dams immediately after birth. Blood samples were taken before initial feeding and at 48 h after birth. Calves were fed 2 L of colostrum twice and milk replacer thereafter. Linear regression of serum IGF-I at 48 h and colostral IGF-I revealed a significant positive relationship (R2 = 0.204). Serum IGFBP-3 at 48 h and colostral IGFBP-3 also had a positive relationship (R2 = 0.143). However, linear regression of colostral IGF-I on the difference in serum IGF-I at 48 and 0 h was not significant. Calves were assigned to group 1 (0-h serum IGF-I < 10 ng/ml; n = 11) or group 2 (0-h serum IGF-I > or = 10 ng/ml; n = 11) for further analysis. There were no differences in serum IGF-I or IGFBP-2, -3, -4, and -5 concentrations at 48 h between groups 1 and 2. Correlation coefficients revealed negative relationships of serum IGF-I at 0 h to the difference between serum IGF-I at 48 and 0 h (r = -0.824), as well as birth weight of the calf to the amount of GGT at 48 h (r = -0.604). Females had lower birth weights than males, but sex of calf did not affect serum measures. At 0 h, but not 48 h, total serum protein was correlated to serum GGT concentrations (r = 0.573). From indirect evidence, absorption of colostral IGF-I and IGFBP-3 into systemic circulation may occur, but relative importance compared to endogenous sources is uncertain.

Influence of gonadotropins on insulin- and insulin-like growth factor-I (IGF-I)-induced steroid production by bovine granulosa cells

To determine the effect of gonadotropins on insulin- and insulin-like growth factor (IGF-I)-induced bovine granulosa cell functions, granulosa cells from bovine ovarian follicles were cultured for 2 days in the presence of 10% fetal calf serum (FCS), and then cultured for an additional 2 days in serum-free medium with added hormones. In the presence of 0 or 1 ng/mL of insulin or IGF-I, FSH had little or no effect (P > 0.05) on estradiol production by granulosa cells from both small (1-5mm) and large (> or = 8mm) follicles. However, in the presence of > or = 3 ng/mL of insulin, FSH increased (P < 0.05) estradiol production by granulosa cells from small and large follicles such that the estimated dose (ED(50)) of insulin necessary to stimulate 50% of the maximum estradiol production was decreased by 2- to 3-fold from 22 to 28 ng/mL in the absence of FSH to 7-14 ng/mL in the presence of FSH. Similarly, in the presence of > or = 3 ng/mL of IGF-I, FSH increased (P< 0.05) estradiol production by granulosa cells from small and large follicles such that the ED(50) of IGF-I for estradiol production was decreased by 4- to 5-fold from 25 to 36 ng/mL in the absence of FSH to 5-6 ng/mL in the presence of FSH. In the presence of FSH, the maximal effect of insulin on estradiol production was much greater than that of IGF-I (137- versus 12-fold increase) and were not additive; when combined, 100 ng/mL of IGF-I completely blocked the stimulatory effect of 100 ng/mL of insulin. In the absence of FSH, the maximal effect of insulin and IGF-I on estradiol production was similar. Concomitant treatment with 30 ng/mL of LH reduced (P<0.05) insulin-stimulated estradiol production by 52% on day 1 and 19% on day 2 of treatment. Insulin, IGF-I and FSH also increased (P<0.05) granulosa cell numbers and progesterone production but their maximal effects were less (i.e., < 4-fold increase) than their effects on estradiol production. In conclusion, insulin and IGF-I synergize with FSH to directly regulate ovarian follicular function in cattle, particularly granulosa cell aromatase activity.

Follicle selection in cattle: dynamics of follicular fluid factors during development of follicle dominance

Follicle diameter deviation during follicular waves in cattle begins with a reduction in growth rates of developing subordinate follicles, in contrast to the maintenance of a constant growth rate by a developing dominant follicle. In experiment 1, the temporal changes encompassing deviation in concentrations of follicular fluid factors relative to one another in the three largest follicles (F1, F2, and F3) were studied. Follicular fluid samples were collected when F1 reached diameter ranges of 7.0-7.9, 8.0-8.9, 9.0-9.9, and 10.0-10.9 mm (n = 12 per range). The first increase (P < 0.05) in the difference between F1 and F2 for estradiol occurred at the 8.0- to 8.9-mm range, which was one range earlier than for diameter (P < 0.05). Free insulin-like growth factor (IGF)-1 concentrations in F1 were similar among diameter ranges, but concentrations in F1 were higher (P < 0.05) than in F2 for each range except 7.0-7.9 mm. Concentrations of free IGF-1 in F2 decreased (P < 0.05). No significant differences were detected in concentrations of progesterone, androstenedione, total inhibin, and inhibin-A. Averaged over follicles, inhibin-B decreased (P < 0.05) between the 8.0- to 8.9- and 10.0- to 10.9-mm ranges, and activin-A increased (P < 0.05) between the 7.0- to 7.9- and 9.0- to 9.9-mm ranges. However, no differences were found among follicles. In experiment 2, changes associated with the development of dominance by F2 were studied using ablation of F1 at the beginning of expected deviation (F1, 8.5 mm; Hour 0) as the reference point. Follicular fluid factors were compared at Hour 12 between F2 of a control group (F1 intact; n = 10) and an ablated group (F1 ablated; n = 10). Diameter (P < 0.02), estradiol (P < 0.001), free IGF-1 (P < 0.002), and progesterone (P < 0.003) were greater and IGF-binding protein-2 was lower (P < 0.01) in F2 of the ablated group at Hour 12. No differences were detected in concentrations of androstenedione, total inhibin, and inhibin-A. The results of the two experiments indicated, on a temporal basis, that intrafollicular changes in estradiol and the IGF system, but not in the inhibin/activin system, could account for a reported greater FSH responsiveness by the future dominant follicle than by the future subordinate follicles by the beginning of diameter deviation in cattle.

Follicular-fluid factors and granulosa-cell gene expression associated with follicle deviation in cattle

Intrafollicular changes in the largest follicle (F1) and second-largest (F2) follicle were examined in relation to follicle diameter deviation. Deviation is characterized by continued growth of the largest follicle and the cessation of growth of the smaller follicles. Granulosa cells and follicular fluid were obtained from slaughterhouse ovaries (n = 95 pairs, experiment 1), and follicular fluid was collected in vivo (n = 28 heifers, experiment 2). Several ranges in the diameter of F1 were used to represent the progressive growth of the follicle. The diameter range with the first significant increase in the difference between F1 and F2 was determined for each end point and was used as an indicator of the sequence of events associated with diameter deviation. An increased difference for diameter and for estradiol concentration occurred (P: < 0.05) simultaneously at the 8.5- to 8.9-mm range in both experiments. In experiment 1, the increased difference between F1 and F2 in LH receptor (LHr) mRNA expression occurred (P: < 0.05) at the 8.0- and 8.4-mm range. In F2 of experiment 2, there was a progressive decrease (P: < 0.05) in free insulin-like growth factor (IGF)-1 and a progressive increase (P: < 0.05) in IGF binding protein (BP)-2 across the follicle-diameter ranges (7.5-11.2 mm). No differences were detected between F1 and F2 for 3beta-hydroxysteroid dehydrogenase mRNA expression in experiment 1 and testosterone, total inhibin, and dimeric inhibin-A concentrations in experiment 2. The results indicated that the acquisition of granulosa cell LHrs by F1, as indicated by increased LHr mRNA expression, occurred one diameter range before an increased difference between F1 and F2 for diameter or estradiol concentrations. On a temporal basis, it is concluded that LHr acquisition plays a role in the establishment of diameter deviation. In addition, the reduced growth of F2 may have involved the reduced bioavailability of IGF-1 in association with elevated IGFBPs.

Follicle selection in cattle: role of luteinizing hormone

The circulating concentrations of LH were reduced by administration of 50 mg of progesterone every 8 h for 72 h, beginning when the largest follicle was 6.0 mm (experiment 1; n = 10). Progesterone treatment prevented the transient increase in LH that accompanied deviation (partitioning into dominant and subordinate categories) in control heifers (n = 10). The reduced LH concentrations were associated with reduced growth of the largest follicle, beginning a mean of 31 h after deviation, but did not alter the time of deviation or the growth and regression of the second-largest follicle. In experiment 2, 0 mg (controls) or 50 mg of progesterone was given every 8 h for three injections, beginning when the largest follicle was 7.0 mm (predeviation group) or 9.0 mm (postdeviation group; n = 8 for each of the four groups). Blood samples from the jugular vein and follicular-fluid samples from the two largest follicles were taken 8 h after the last treatment when the largest follicle was a mean of 8.7 mm in the predeviation group and 10.8 mm in the postdeviation group. In the controls, follicular-fluid concentrations of estradiol and free insulin-like growth factor (IGF)-1 in the largest follicle and IGF binding protein (IGFBP)-2 in the second-largest follicle were higher (P: < 0.05) in the postdeviation group than in the predeviation group. Progesterone treatment lowered (P: < 0.006) the circulating LH concentrations to a similar extent in both groups. In the predeviation group, progesterone treatment did not have a significant effect on any of the characteristics of the largest follicle. In the postdeviation group, the largest follicle of the progesterone-treated heifers had significant reductions in diameter and in follicular-fluid concentrations of estradiol and free IGF-1. Follicular-fluid concentrations of immunoreactive inhibin were not different for any of the comparisons. The results supported the hypothesis that LH has a positive effect on diameter of the largest follicle but not until after the beginning of diameter deviation. In addition, the results indicated that LH is involved in the production of estradiol by the largest follicle and that free IGF-1 concentrations increase in the largest follicle during deviation.