Circulating concentrations of inhibin-related proteins during the ovulatory cycle of the domestic fowl (Gallus domesticus) and after induced cessation of egg laying

Circulating inhibin A, inhibin B, activin A, total immunoreactive inhibin alpha-subunit (ir-alpha inhibin), LH, FSH and progesterone concentrations were measured throughout the normal ovulatory cycle and after cessation of egg laying induced by feed restriction to investigate the potential involvement of inhibins and activins in the ovulatory cycle of the domestic hen. Plasma inhibin A varied significantly (P < 0.05) during the ovulatory cycle; the concentration was highest at the preovulatory LH surge and reached a nadir 10 h later, at about the time the F(2) follicle makes the transition to become the new F(1) follicle. Plasma FSH concentrations did not change significantly throughout the cycle and showed no correlation with inhibin A. Total ir-alpha inhibin concentrations were much higher than those of inhibin A at all stages of the ovulatory cycle and showed no correlation with inhibin A or FSH. Plasma concentrations of inhibin B and of activin A were below the detection limit of the assays in all plasma samples analysed. In the feed restriction study, plasma inhibin A and total ir-alpha inhibin showed little change until the last day of oviposition (day 0) after which they fell significantly (P < 0.05) and remained low to the end of the experiment (approximately 70-78% decrease relative to day -4). Conversely, plasma FSH increased after cessation of laying and was significantly higher (P < 0.05) from day 3 to the end of the study (approximately 50% increase on day 6 relative to day -4). Plasma FSH values were negatively correlated with inhibin A (r = -0.39; P < 0.005) and total ir-alpha inhibin (r = -0.36; P < 0.005). Plasma LH and progesterone also decreased (P < 0.05) during feed restriction. The decrease in LH preceded the terminal oviposition and the associated fall in inhibin A by 2 days; there was a positive correlation between LH and inhibin A (r = 0.35; P < 0.005). Taken together these findings support (i) a role for LH in promoting inhibin A secretion by preovulatory follicles and (ii) an endocrine role for inhibin A secreted by preovulatory follicles in the maintenance of tonic FSH secretion in laying hens.     

A deletion mutation in GDF9 in sisters with spontaneous DZ twins.

A loss of function mutation in growth differentiation factor 9 (GDF9) in sheep causes increased ovulation rate and infertility in a dosage-sensitive manner. Spontaneous dizygotic (DZ) twinning in the human is under genetic control and women with a history of DZ twinning have an increased incidence of multiple follicle growth and multiple ovulation. We sequenced the GDF9 coding region in DNA samples from 20 women with DZ twins and identified a four-base pair deletion in GDF9 in two sisters with twins from one family. We screened a further 429 families and did not find the loss of function mutation in any other families. We genotyped eight single nucleotide polymorphisms across the GDF9 locus in 379 families with two sisters who have both given birth to spontaneous DZ twins (1527 individuals) and 226 triad families with mothers of twins and their parents (723 individuals). Using case control analysis and the transmission disequilibrium test we found no evidence for association between common variants in GDF9 and twinning in the families. We conclude that rare mutations in GDF9 may influence twinning, but twinning frequency is not associated with common variation in GDF9.     

Plasma concentrations of inhibin a and follicle-stimulating hormone differ between cows with two or three waves of ovarian follicular development in a single estrous cycle

Patterns of ovarian follicle development were monitored daily in Holstein-Friesian cows that had two (n = 4) or three (n = 4) waves of ovarian follicle development during a single estrous cycle. The plasma from daily blood samples was used in assays for inhibin A, FSH, progesterone, and estradiol-17beta. Mean cycle lengths for cows with two and three waves were 21.8 and 25.3 days, respectively (P < 0.02). Although the average number of follicles >3-mm diameter on each pair of ovaries was similar for two- and three-wave cows on Days 2, 3, and 4 (Day 0 = day of ovulation; 8.6 vs. 9.6 follicles), there were more follicles >6-mm diameter on the ovaries of cows with two waves on Days 3 and 4. This difference was associated with a shorter interval from wave emergence to peak concentrations of inhibin A during the first wave in two-wave cows (2.0 vs. 3.8 days; P = 0.03) and with higher peak concentrations (474 vs. 332 pg/ml; P = 0.03). Differences in peak FSH concentrations were not significant (1.7 vs. 1.3 ng/ml; P = 0.10) and were inversely related to inhibin A concentrations. The peak concentrations of inhibin A and FSH in the second nonovulatory wave in the three-wave cows were similar to the low concentrations measured in the first wave (292 vs. 332 pg/ml of inhibin A, 1.3 vs. 1.3 ng/ml of FSH; P > 0.20). Average peak concentrations of inhibin A and FSH were similar during the ovulatory wave for cows with either two or three waves in a cycle (432 vs. 464 pg/ml of inhibin A, 2.3 vs. 2.1 ng/ml of FSH; P > 0.3). The lower concentrations of FSH during the emergence of the first follicular wave in cows with three-wave cycles may have reduced the rate of development of some of the follicles and reduced the concentrations of inhibin A. This pattern of lower concentrations of FSH and inhibin A was repeated in the second nonovulatory wave but not in the ovulatory wave. Subtle differences in the concentrations of these two hormones may underlie the mechanism that influences the number of waves of ovarian follicle development that occur during the bovine estrous cycle.     

Alterations in peripheral concentrations of inhibin A in cattle studied using a time-resolved immunofluorometric assay: relationship with estradiol and follicle-stimulating hormone in various reproductive conditions

The aims of this study were to develop a sensitive and specific assay for bovine inhibin A using europium and to investigate the endocrine role of inhibin A in various reproductive conditions by characterizing the relationship between profiles of inhibin A, FSH, and estradiol and follicle growth during the postpartum period, during the intact estrous cycle, and in cows with follicular cysts. The time-resolved immunofluorometric assay (Tr-IFMA) for bovine inhibin A, using purified polyclonal antibodies to alpha and beta(A) subunits, was specific for bovine inhibin A and did not cross-react with bovine activin A, activin AB, activin B, pro-alphaC or human recombinant inhibin B. The detection limit of the IFMA was 3.3 pg/ml expressed in terms of bovine 32-kDa inhibin A. Dose-response curves of plasma samples obtained from intact and FSH-stimulated cows and cystic cows were parallel to the standard without any preassay processing of samples. Plasma inhibin A levels increased (P < 0.01) concomitant with emergence of nonovulatory or ovulatory follicular waves during the postpartum period. In cystic cows, plasma inhibin A was sustained at high levels for a longer period, associated with growth of persistent dominant follicles. The highest levels of inhibin A were noted during the growth phase of normal and persistent dominant follicles; however, inhibin A levels declined (P < 0.01) as these dominant follicles ceased to grow or ovulated. An inverse relationship between patterns of plasma inhibin A and FSH existed during each follicular wave in the three physiologic conditions. Increases in plasma inhibin A levels were associated with increases in plasma estradiol levels during most follicular waves; however, there was no increase in plasma estradiol level and no relationship between patterns of estradiol and FSH during follicular waves observed during the early postpartum period or midluteal phase of the estrous cycle. In conclusion, the Tr-IFMA does not require pretreatment of samples and can be used for precise measurement of bovine inhibin A without interference with free inhibin alpha subunits. Inhibin A, produced primarily during growth of the dominant follicle, functions as a negative feedback regulator for FSH secretion throughout the postpartum period and the estrous cycle, whereas estradiol appears to have a minor role in regulation of FSH compared with inhibin A, especially during the early postpartum period and midluteal phase of the estrous cycle. The results also indicate that a persistent dominant follicle sustains inhibin A production for a longer period than the dominant follicle emerging in the estrous cycle and establishes long-term dominance by suppressing emergence of a new follicular wave.     

Gonadotropin control of inhibin secretion and the relationship to follicle type and number in the hpg mouse

Inhibin is secreted in two distinct heterodimeric forms, A and B, but the mechanism for the differential control of these two forms is unclear. To evaluate the relationship between secretion of inhibin forms and folliculogenesis, the effects of gonadotropins on inhibin concentrations were studied in parallel with stereological enumeration of ovarian follicle types in gonadotropin-deficient hypogonadal (hpg) female mice treated with recombinant human FSH (10 IU/day), hCG (1 IU/day), or both for 20 days. Treatment with FSH alone significantly increased blood concentrations of both inhibin A and inhibin B, whereas hCG alone had no effect on either inhibin. The combination of FSH and hCG further increased the concentration of inhibin A but had no effect on the concentration of inhibin B beyond that of FSH. The number of primordial follicles per ovary was significantly reduced in FSH-treated hpg mice, but was not affected by hCG treatment. Antral follicles were absent in the untreated hpg mice, present following treatment with FSH, and were present in only limited numbers following hCG treatment alone. Preovulatory follicles were observed only in the wild-type and combined FSH and hCG treatment groups. These results demonstrate that secretion of both inhibins is associated with the presence of antral follicles. Inhibin A secretion is increased by the presence of preovulatory follicles, whereas the concentration of inhibin B is not affected. The observed effects of gonadotropins on inhibin A and B secretion may be explained by corresponding gonadotropin effects on follicle development.     

Interrelationships of estradiol, inhibin, and gonadotropins during follicle deviation in pony mares

The changes in circulating concentrations of FSH, LH, estradiol, and total inhibin associated with the beginning of follicle diameter deviation were compared among the last anovulatory follicular wave of the year and the first and second ovulatory waves in pony mares ( n=7 ). Follicle diameters and circulating hormone concentrations for each wave were normalized to the observed beginning of deviation (Day 0). Follicle deviation was demonstrated during the anovulatory wave as well as during the ovulatory waves, and the diameter of the future dominant follicle at the beginning of deviation was similar for the three waves (overall mean: 23.7+/-0.6 mm). Circulating estradiol concentrations did not increase during the last anovulatory wave but increased similarly for the two ovulatory waves, beginning near the onset of deviation. There were no differences among waves in concentrations of inhibin encompassing deviation. The FSH concentrations for the wave-stimulating FSH surge did not differ significantly among the three waves; combined for the three waves, concentrations decreased between Days -3 and 7. Circulating LH did not increase during the last anovulatory wave but increased during the first and second ovulatory waves beginning on Days 6 and -2, respectively. Results indicated that the increase in circulating estradiol at the beginning of deviation was not required for suppression of the wave-stimulating FSH surge and the initiation of deviation, based on an estradiol increase in association with deviation during the ovulatory waves but not during the anovulatory wave. Concentrations of inhibin were similar among waves and, therefore on a temporal basis, the similar suppression of FSH was attributable to inhibin. The later increase in LH before the first ovulation was not attributable to estradiol, based on the similarity between the two ovulatory waves in the increasing estradiol concentrations.     

Concentrations of gonadotropins,estradiol and progesterone in sows selected on an index of ovulation rate and embryo survival

The objective of this study was to determine concentrations of follicle stimulating hormone (FSH), luteinizing hormone (LH), progesterone (P₄) and 17β-estradiol (E₂) in sows from a line selected on an index which emphasized ovulation rate (Select) and from a control line. A further classification of the sows in each line was made according to the estimated number of ovulations during an estrous cycle. Sows in the Select line were ranked into a high (HI) or low group (LI) when their estimated number of ovulations were 25 or more and 14 to 15, respectively. Sows of the control line were classified into groups as high (HC) or low (LC) when the estimated values for ovulation rate were 14–15 and 8–9 ovulations, respectively. Blood samples were collected every 12 h during a complete estrous cycle and samples were analyzed for concentrations of FSH and LH. Samples collected every 24 h were assayed for P₄ and E₂. Mean concentrations of FSH, LH, P₄ and E₂ did not differ (P>0.10) between lines or between HI and LI or HC and LC groups. Selection of pigs for ovulation rate and embryonal survival did not affect concentrations of FSH, LH, P₄ and E₂ in sows during the estrous cycle.     

Twinning rates in a rural area of Bangladesh

In this study we investigate the incidence of twin births over a period of 16 years in a rural area of Bangladesh using data from the Demographic Surveillance System of the International Centre for Diarrhoeal Disease Research. Over the study period twinning rates fluctuated between 7.8 and 11.2 per 1000 live births. The twinning rate was strongly correlated with maternal age; the rate for mothers over 35 years of age was about 3 times higher than for mothers younger than 20 years. The variation in twinning rate with maternal age is due to the variation in dizygotic twinning; the rate of monozygotic twinning is almost constant for all ages. Twinning rates were higher in the treatment area than in the comparison area after controlling for maternal age and parity. The rates were lower for monozygotic twinning and higher for dizygotic twinning in the treatment area than in the comparison area. Seasonality was observed for both twins and singletons, but the peak for twinning precedes that for singleton births by more than a month.     

Role of increased estradiol on altering the follicle diameters and gonadotropin concentrations that have been reported for double-ovulating heifers

During the preovulatory period in heifers that ovulate from two compared to one follicle, circulating concentrations of estradiol-17β (E2) are greater, diameter of follicles and concentration of FSH are reduced, and the LH surge occurs sooner. The effect of increased E2 on the reported characteristics of double ovulation was studied by treating heifers with 0.07 mg E2, 0.09 mg E2, or vehicle in four treatments at 6-h intervals (n=6 heifers/group), beginning at the time of expected follicle deviation (largest follicle, 8.5mm). There were no significant differences on follicle diameters or hormone concentrations between the 0.07 and 0.09 mg E2 groups, and heifers were combined into one E2 group (n=12). The E2 treatments induced concomitant preovulatory surges in LH and FSH at 34.0 ± 2.6h after first treatment, compared to 57.6 ± 4.5h in the vehicle group (P<0.0002). The E2 treatments did not affect FSH concentrations during the preovulatory gonadotropin surge. The diameter of the preovulatory follicle at the LH peak was smaller (P<0.0001) in the E2-treated group (10.2 ± 0.2mm) than in the vehicle group (13.1 ± 0.6mm). The hypothesis was not supported that the previously reported increase in circulating E2 in heifers with double preovulatory follicles accounts for the reported lesser concentrations in the preovulatory FSH surge in heifers with double ovulations. Hypotheses were supported that the reported earlier occurrence of the preovulatory LH surge and smaller preovulatory follicles in heifers with double ovulations are attributable to the reported increase in E2 from the double preovulatory follicles.     

Follicle diameters and hormone concentrations in the development of single versus double ovulations in mares

Relationships between double ovulations and plasma hormone concentrations were compared between 18 single ovulating and 6 double ovulating mares. The study began when the first follicle reached >or=30 mm, and ultrasound scanning and blood sampling were done every 12h to Day 3 (ovulation=Day 0). Data were analyzed for 2.5 d after the largest follicle was >or=30 mm and after Day -2.5 to encompass the mean 5-d interval between a >or=30 mm follicle and Day 0. During the 2.5 d after >or=30 mm, the increasing diameter of the largest follicle was less pronounced and plasma FSH concentrations were lower (approached significance) in the double ovulators than in the single ovulators. By Day -2.5, the largest follicle was smaller (P<0.01) and plasma FSH was lower (P<0.04) in the double ovulators. Plasma estradiol concentrations were higher (P<0.001) during the 2.5 d after >or=30 mm in the double ovulators and the correlation between estradiol and FSH was negative (r=-0.39, P<0.0001). In double ovulators, compared to single ovulators, the largest follicle was smaller, FSH was lower and estradiol was higher on most occasions between Days -2.5 and -0.5 (P<0.05), but plasma concentrations of LH and ir-inhibin were not significantly different. In conclusion, smaller preovulatory follicles in double ovulators were a response to lower FSH concentrations, due to higher estradiol concentrations from two preovulatory follicles; preovulatory differences in hormone concentrations between single and double ovulators were an effect rather than a cause of the double ovulations.     

Twinning in humans: maternal heterogeneity in reproduction and survival

While humans usually give birth to singletons, dizygotic twinning occurs at low rates in all populations worldwide. We evaluate two hypotheses that have differing expectations about the effects of bearing twins on maternal lifetime reproduction and survival. The maternal depletion hypothesis argues that mothers of twins will suffer negative outcomes owing to the higher physiological costs associated with bearing multiples. Alternatively, twinning, while costly, may indicate mothers with a greater capacity to bear that cost. Drawing from the vast natural fertility data in the Utah Population Database, we compared the reproductive and survival events of 4603 mothers who bore twins and 54 183 who had not. These mothers were born between 1807 and 1899, lived at least to the age of 50 years and married once to men who were alive when their wives were 50. Results from proportional hazards and regression analyses are consistent with the second hypothesis. Mothers of twins exhibit lower postmenopausal mortality, shorter average inter-birth intervals, later ages at last birth and higher lifetime fertility than their singleton-only bearing counterparts. From the largest historical sample of twinning mothers yet published, we conclude that bearing twins is more likely for those with a robust phenotype and is a useful index of maternal heterogeneity.     

Elevated inhibin concentration in the follicular fluid of dairy cows with chronic cystic ovarian disease

This study compared serum and follicular fluid inhibin and gonadotropin profiles between chronic cystic ovarian diseased (CCOD) and normal cyclic dairy cows. Blood samples and follicular fluid were collected from CCOD cows (n=15) and cyclic cows in the follicular phase of the estrous cycle (control, n=6) and analyzed for inhibin, follicle stimulating hormone (FSH) and luteinizing hormone (LH) concentrations. There was a significant increase in inhibin and a decrease in FSH and LH concentrations in the follicular fluid of CCOD cows compared with those of cyclic cows (P < 0.05). Mean serum inhibin, FSH and LH concentrations between CCOD and cyclic cows were not differnt (P > 0.05), however, there was a tendency for serum inhibin to be higher and FSH to be lower in CCOD cows compared to cyclic animals (P < 0.1). The FSH pulse frequency also was lower in CCOD cows than in cyclic cows (P < 0.05). These data suggest that increased production of inhibin from cystic follicles of CCOD cows alters pituitary FSH secretion and subsequently reduces the concentration of FSH in follicular fluid. As a result, decreased FSH stimulation at the ovarian level could ultimately lead to the reduction in follicular LH and FSH receptor concentrations, resulting in abnormal follicular steroidogenesis in CCOD dairy cows.     

Hormone secretion in the asian elephant (Elephas maximus): characterization of ovulatory and anovulatory luteinizing hormone surges.

In the elephant, two distinct LH surges occur 3 wk apart during the nonluteal phase of the estrous cycle, but only the second surge (ovLH) induces ovulation. The function of the first, anovulatory surge (anLH) is unknown, nor is it clear what regulates the timing of these two surges. To further study this observation in the Asian elephant, serum concentrations of LH, FSH, progesterone, inhibin, estradiol, and prolactin were quantified throughout the estrous cycle to establish temporal hormonal relationships. To examine long-term dynamics of hormone secretion, analyses were conducted in weekly blood samples collected from 3 Asian elephants for up to 3 yr. To determine whether differences existed in secretory patterns between the anLH and ovLH surges, daily blood samples were analyzed from 21 nonluteal-phase periods from 7 Asian elephants. During the nonluteal phase, serum LH was elevated for 1-2 days during anLH and ovLH surges with no differences in peak concentration between the two surges. The anLH surge occurred 19.9+/-1.2 days after the end of the luteal phase and was followed by the ovLH surge 20.8+/-0.5 days later. Serum FSH concentrations were highest at the beginning of the nonluteal phase and gradually declined to nadir concentrations within 4 days of the ovLH surge. FSH remained low until after the ovLH surge and then increased during the luteal phase. Serum inhibin concentrations were negatively correlated with FSH during the nonluteal phase (r = -0.53). Concentrations of estradiol and prolactin fluctuated throughout the estrous cycle with no discernible patterns evident. In sum, there were no clear differences in associated hormone secretory patterns between the anLH and ovLH surge. However, elevated FSH at the beginning of the nonluteal phase may be important for follicle recruitment, with the first anLH surge acting to complete the follicle selection process before ovulation.     

Inhibin B,follicle stimulating hormone,luteinizing hormone,and estradiol and their relationship to the regulation of follicle development in girls during childhood and puberty

Inhibin B, produced by granulosa cells in the ovary, is a heterodimeric glycoprotein suppressing synthesis and secretion of the follicle stimulating hormone (FSH). The aim of the present study was to determine hormone profiles of inhibin B, FSH, luteinizing hormone (LH), and estradiol in girls during childhood and puberty and to evaluate whether inhibin B is a marker of follicle development. We examined the correlation between inhibin B and gonadotropins and estradiol during the first two years and across the pubertal development. Using a specific two-side enzyme-linked immunosorbent assay (ELISA), inhibin B levels were measured in the serum of 53 healthy girls divided into 8 groups according to age. In addition, serum FSH, LH, and estradiol were measured by chemiluminescent immunoassay in all serum samples. A rise in serum levels of inhibin B (55.2+/-7.3 ng/l, mean +/- S.E.M.) and FSH (1.78+/-0.26 UI/l), concomitant with a moderate increment of serum LH (0.36+/-0.09 UI/l) and estradiol (45.8+/-12.2 pmol/l) concentrations was observed during the first three months of life and declined to prepubertal concentrations thereafter. A strong positive correlation between inhibin B and FSH (r = 0.48, p<0.05), LH (r = 0.68, p<0.001) and estradiol (r = 0.59, p<0.01) was demonstrated during the first 2 years of life. A rise in serum levels of inhibin B, FSH, LH, and estradiol was found throughout puberty. Inhibin B had a strong positive correlation with FSH (stage I of puberty: r = 0.64, p<0.05; stage II of puberty: r = 0.86, p<0.01), LH (I: r = 0.61, p<0.05; II: r = 0.67, p<0.05), and estradiol (II: r = 0.62, p<0.05) in early puberty. From pubertal stage II, inhibin B lost this relationship to gonadotropins and estradiol. Serum inhibin B and FSH levels increased significantly during pubertal development, with the highest peak found in stage III of puberty (133.5+/-14.3 ng/l), and decreased thereafter. In conclusion, inhibin B is produced in a specific pattern in response to gonadotropin stimulation and plays an important role in the regulation of the hypothalamic-pituitary-gonadal axis during childhood and puberty in girls. Inhibin B is involved in regulatory functions in developing follicles and seems to be a sensitive marker of ovarian follicle development.     

Inhibitory effect of obesity on gonadotropin, estradiol, and inhibin B levels in fertile women

Objective: To examine whether obesity and insulin resistance have an independent effect on the gonadotropin, estradiol, and inhibin B serum levels and follicle count in the early follicular phase of fertile women with a wide range of BMI and without signs of hyperandrogenism. Research Methods and Procedures: Twenty‐two overweight and obese (BMI ≥25.0 kg/m²) women and 10 normal‐weight (BMI <25.0 kg/m²) women, all having apparently normal fertility, were studied. Serum concentrations of follicle‐stimulating hormone (FSH), luteinizing hormone (LH), estradiol, inhibin B, and insulin, level of insulin resistance (estimated by homeostasis model assessment for insulin resistance), and follicle count were measured during the early follicular phase (Days 2 to 5 of the menstrual cycle). Results: Overweight women showed lower FSH (p < 0.001), LH (p < 0.001), and inhibin B (p < 0.05) levels compared with normal‐weight women, whereas estradiol concentrations and follicle count were not significantly different between the two groups. When normal‐weight and overweight women were examined as a group and multiple regression analyses were performed, estradiol showed a negative association with BMI (or waist circumference) (p < 0.05) and a positive correlation with LH (p < 0.05) and FSH (p < 0.05); inhibin B maintained a positive association only with estradiol (p < 0.05); and FSH and LH showed a negative correlation with BMI (or waist circumference) (p < 0.001 and p < 0.01, respectively). Discussion: Overweight and obese fertile women have lower FSH, LH, inhibin B, and estradiol levels in the early follicular phase, with a possible direct inhibitory effect of body mass on gonadotropin and estradiol production, independently of age, insulin (concentrations and sensitivity), and other hormones. By contrast, the number of ovary follicles does not seem to be influenced by insulin and body mass in these patients.     

Genetic risk factors in tumours of the testis: lessons from twin studies.

A threefold increase for testicular carcinoma has been reported in male dizygotic twins. In this comment we suggest the hypothesis that over-exposure to endogenously hypersecreted Follicle Stimulating Hormone (FSH) may underlie the pathogenesis. This is supported by several findings. 1) FSH hypersecretion in mothers of dizygotic twins is most likely an autosomal trait implicating the possibility of male offspring with the same hormone characteristic. 2) In testicular carcinoma higher levels of cyclin D2 are found. This is an FSH dependent stimulatory regulator of mitosis. 3) There is a marked similarity between geographical distribution in occurence of dizygotic twinning and testicular carcinoma. 4) Men undergoing surgery for testicular carcinoma have higher FSH concentrations and males with Down syndrome have higher FSH levels and are more at risk to develop testicular carcinoma. We suggest to study FSH secretion in males of familial dizygotic twins and furthermore the risk of developing testicular carcinoma in males with elevated FSH. These men with one testicle and/or with dysfunctioning Sertoli/Leydig cells.     

Effect of inhibin immunisation using different synthetic peptide fragments of the bovine αc-subunit on plasma anti-inhibin titres,plasma FSH concentrations and the incidence of multiple ovulation in heifers

In an effort to improve the effectiveness of inhibin immunisation in promoting multiple ovulation in cattle and to clarify the mechanism(s) involved, heifers (n = 5 per group) were immunised against ovalbumin conjugates of different synthetic peptide sequences of the α_c-subunit of bovine inhibin (bIα) selected using antigenic prediction methods. Plasma inhibin antibody titre (percentage binding of ¹²⁵I-labelled M_r 32 000 native bovine inhibin), plasma follicle-stimulating hormone (FSH) concentration and ovulatory response (number of corpora lutea observed by transrectal ovarian ultrasonography) were recorded over a 16 week period.Heifers immunised against the bIα1–29 and 63–72 peptides (alone or in combination), had relatively high anti-inhibin titres (over 7.5% binding) and showed a significantly (P < 0.05) increased incidence of multiple ovulations (18–65%) compared with ovalbumin-immunised controls. However, immunisation against the 1–16 and 108–123 peptides was relatively ineffective in generating antibodies reactive with native inhibin (less than 7.5% binding) and gave little or no increase in incidence of multiple ovulations (0–10%).Analysis of results for all 33 heifers revealed a significant linear relationship between mean inhibin antibody titre and mean plasma FSH concentration (r = 0.42; P < 0.02) and between mean inhibin antibody titre and incidence of multiple ovulation (r = 0.89; P < 0.0001). A significant quadratic relationship existed between mean inhibin antibody titre and the mean number of ovulations per cycle (r = 0.88; P < 0.0001). However, partial correlation analysis showed a highly significant association between anti-inhibin titre and ovulatory response which was independent of changes in mean plasma FSH concentrations.These results extend previous studies involving inhibin peptide-immunised cattle by showing that the magnitude of the ovulatory response is directly related to the prevailing titre of antibodies reactive with native inhibin. However, they do not support the hypothesis that the ovulatory response is mediated solely by a rise in FSH secretion.     

Reproductive hormone genes in mothers of spontaneous dizygotic twins: an association study

There are important genetic influences on the tendency to dizygotic (DZ) twinning and it is a plausible hypothesis that these reside in one or more of the genes coding for the major reproductive hormones. We used Southern analysis of DNA from 50 young (<32) mothers of DZ twins, who also had a family history of DZ twinning, and 50 controls, to examine allele frequencies of five restriction fragment length polymorphisms (RFLPs) in four hormone genes coding for follicle stimulating hormone (FSH), chorionic gonadotropin (CGB), inhibin _B and gonadotropin releasing hormone (GnRH). Comparison of allele frequencies revealed no significant differences between DZ twin mothers and controls. However this does not rule out the role of these genes in the hereditary tendency of multiple ovulation in humans, since absence of linkage disequilibrium does not imply absence of linkage.     

Concentrations of immunoreactive inhibin in ovarian and peripheral venous plasma and follicular fluid of Booroola ewes that are homozygous carriers or non-carriers of the FecB gene.

No gene-specific differences were found during either the luteal or follicular phases of the oestrous cycle in the venous secretion rates of ovaries or in concentrations of immunoreactive inhibin in peripheral plasma between Booroola ewes that were homozygous carriers (BB) or non-carriers (++) of the FecB gene. In three experiments in which concentrations of plasma inhibin and follicle-stimulating hormone (FSH) were compared, gene-specific differences were noted for FSH (P less than 0.05), but no significant correlations were noted between FSH and inhibin for either genotype. Granulosa cells and follicular fluid, but not theca interna, stroma or corpora lutea, were the major intra-ovarian sites of inhibin; no gene-specific differences were noted for inhibin concentrations in follicular fluid or in any of the intra-ovarian tissues. The mean concentrations of inhibin in follicular fluid remained constant irrespective of follicular diameter whereas the mean total contents of inhibin increased significantly with increasing diameter (P less than 0.05). Inhibin secretion rates were four times higher in ovaries with oestrogen-enriched follicles (i.e. greater than or equal to 50 ng oestradiol ml-1) than in ovaries with no such follicles (P less than 0.01). Moreover, inhibin concentrations were higher in follicular fluid of oestrogen-enriched follicles than in those with low oestrogen (i.e. less than 50 ng ml-1; P less than 0.05). Ovariectomy resulted in a significant reduction in concentrations of immunoreactive inhibin from plasma (P less than 0.01). The residual plasma inhibin in some Booroola ewes was not associated with genotype. It is concluded that, although antral follicles are a major source of inhibin in Booroola ewes, immunoreactive inhibin is not associated with the FecB gene and is not responsible for the gene-specific differences in concentrations of FSH in plasma.