Serum inhibin A and inhibin B in healthy prepubertal, pubertal, and adolescent girls and adult women: relation to age, stage of puberty, menstrual cycle, follicle-stimulating hormone, luteinizing hormone, and estradiol levels

Biochemical assessment of gonadal function during maturation in girls and in adult women can be troublesome. With the recent advent of specific assays for the gonadal peptides inhibin A and inhibin B, it might be possible to achieve a clearer picture of events. We therefore determined serum levels of inhibin A, inhibin B, FSH, LH and estradiol in a cross-sectional study of 403 healthy schoolgirls (aged 6 -20 yr) in relation to age and stage of puberty and in 181 healthy nonpregnant women (aged 20-32 yr) in relation to stage of the menstrual cycle. In addition, inhibin A and inhibin B were measured daily throughout the menstrual cycle in 10 healthy adult women. Levels of inhibin B are low or undetectable in prepubertal girls (median, 26.5 pg/mL; 95% prediction interval, <20-100 pg/mL), increase sharply through pubertal stage II to peak in stage III (median, 84 pg/mL; 95% prediction interval, 28-227 pg/mL) and thereafter decline through pubertal stages IV and V. These changes presumably reflect increasing ovarian stimulation through early puberty, resulting in an increased number of developing follicles, follicles reaching a later stage of development before undergoing atresia, or both. Declining levels in late puberty and adulthood probably reflect the onset of the menstrual cycle and the subsequent appearance of the luteal phase, where inhibin B levels are low. Inhibin A levels are undetectable or very low in early puberty (median, <7 pg/mL; 95% prediction interval, <7-14) pg/mL), increasing gradually through pubertal stages to reach their highest values in adult women (median, 21.5 pg/mL; 95% prediction interval, <7-129 pg/mL). Levels of inhibin A greater than 19 pg/mL are only seen in postmenarcheal girls in puberty and in adult women, again consistent with inhibin A being primarily produced by the corpus luteum. Determining cut-off levels of serum inhibin B regarding whether a girl had entered puberty resulted in similar (low) sensitivities and specificities as those found for cut-off levels of LH or estradiol due to the large overlap between serum values in Tanner stages I and II. Correlations between inhibin A and inhibin B and FSH, LH, and estradiol within pubertal stages are presented. In early puberty both inhibin A and inhibin B correlated positively with LH and FSH. In late puberty inhibin A correlated negatively with FSH and did not correlate with LH; inhibin B still correlated positively with both FSH and LH, now most strongly with FSH. In adult women during the menstrual cycle, serum inhibin B levels increased during the follicular phase, indicating the greatest production by follicles in early stages of development. In contrast, serum inhibin A levels peaked during the luteal phase, indicating the greatest production by the corpus luteum. In conclusion, serum inhibin A and inhibin B levels in normal puberty in girls show consistency with our knowledge of the manner in which these hormones are secreted within the menstrual cycle in adult women. The presented reference values may be of use in the clinical evaluation of pubertal development in girls.     

Ovarian follicular concentrations of activin, follistatin, inhibin, insulin-like growth factor I (IGF-I), IGF-II, IGF-binding protein-2 (IGFBP-2), IGFBP-3, and vascular endothelial growth factor in spontaneous menstrual cycles of normal women of advanced reproductive age

Previous studies indicate that the menstrual cycles of older reproductive age women are characterized by a selective elevation of FSH associated with early development and ovulation of a dominant follicle. Several intraovarian hormones and growth factors have been identified that appear to serve important paracrine roles. The purpose of this study was to examine follicular fluid (FF) hormones and growth factors in the dominant follicle of unstimulated cycles of older, ovulatory women. We aspirated FF from the preovulatory dominant follicle in natural menstrual cycles of older subjects (age, 40-45 yr; n = 20) and younger controls (age, 20-25 yr; n = 19). FF was analyzed for estradiol, progesterone, testosterone, androstenedione, inhibin A and B, total activin A, total follistatin, insulin-like growth factor I (IGF-I), IGF-II, IGF-binding protein-2 (IGFBP-2), IGFBP-3, and vascular endothelial growth factor (VEGF) concentrations. We found that the dominant follicles from older women contain normal concentrations of steroids, inhibin A and B, IGF-II, IGFBP-2, and IGFBP-3; increased concentrations of follistatin, activin A, and VEGF; and decreased concentrations of IGF-I. Therefore, under the influence of elevated FSH, the dominant follicle in older women is highly competent in terms of hormone and growth factor secretion. We postulate that elevated FF activin may be related to the early ovulation observed in older women, whereas elevated VEGF may be related to the meiotic spindle abnormalities observed in the oocytes of older reproductive age women.     

A common single nucleotide polymorphism in exon 10 of the human follicle stimulating hormone receptor is a major determinant of length and hormonal dynamics of the menstrual cycle

CONTEXT: FSH is essential for follicular maturation. Data from ovarian hyperstimulation cycles suggest that FSH action is attenuated by a frequent single nucleotide polymorphism of the FSH receptor gene exchanging Asn for Ser at codon 680. OBJECTIVE: We hypothesized that the FSH receptor genotype influences menstrual cycle dynamics. DESIGN: Menstrual cycle was monitored from the midluteal phase through ovulation until the consecutive menstruation. SETTING: The study was conducted at the University research center. SUBJECTS: Women homozygous for the Asn680 (n = 12) and Ser680 (n = 9) variants with normal menstrual cycles volunteered for the study. INTERVENTIONS: There were no interventions. MAIN OUTCOME MEASUREMENTS: Follicular growth, serum LH, FSH, estradiol, progesterone, inhibin A, inhibin B and antimullerian hormone were measured. RESULTS: During the luteo-follicular transition, serum levels of estradiol, progesterone, and inhibin A were significantly lower, and FSH started to rise earlier in the Ser680/Ser680 group. FSH levels were steadily and significantly higher, and the mean area under the FSH curve was 31% greater in this group (P < 0.002). No differences were observed in estradiol, inhibin B, and growth velocities of dominant follicles. The time from luteolysis to ovulation was significantly longer in women with the Ser680/Ser680 (13.6 +/- 1.01 d) compared with Asn680/Asn680 (11.3 +/- 0.61 d, P < 0.05) genotype with a significant difference in total menstrual cycle length (29.3 vs. 27.0 d, respectively; P < 0.05). CONCLUSIONS: The FSH receptor Ser680/Ser680 genotype is associated with higher ovarian threshold to FSH, decreased negative feedback of luteal secretion to the pituitary during the intercycle transition, and longer menstrual cycles.     

Relationship between inhibin A and B, estradiol and follicle growth dynamics during ovarian stimulation in normo-ovulatory women

OBJECTIVE: To investigate the relationship between serum concentrations of inhibin A, inhibin B and estradiol (E(2)) and the number of developing follicles during the administration of exogenous follicle-stimulating hormone (FSH) in various regimens in normo-ovulatory volunteers and to evaluate if inhibins act as suitable markers for the number of developing follicles during ovarian stimulation. DESIGN AND METHODS: Serial hormone determinations and assessment of follicle numbers were carried out during unstimulated cycles and during various interventions with exogenous FSH. Subjects were randomized for FSH administration into the following groups: a single high dose (375 IU) during the early follicular phase (group A), 5 consecutive low doses (75 IU/day) starting in the mid follicular phase (group B) or daily low doses (75 IU/day) during the early to late follicular phase (starting on cycle days 3, 5 or 7; groups C, D and E respectively). RESULTS: Extending the FSH window increases the number of small antral follicles and hence inhibin B serum concentrations. If such an intervention results in multi-follicular growth, mid follicular phase inhibin B (P = 0.001) as well as late follicular phase inhibin B and inhibin A levels are significantly (P < 0.05 and P < 0.01 respectively) increased compared with mono-follicular cycles or the natural cycle. Although mid follicular inhibin B levels correlated well with the number of small antral (P < 0.05) and pre-ovulatory (P < 0.001) follicles in the late follicular phase, mid follicular inhibin A and estradiol serum concentrations only correlated with the number of pre-ovulatory follicles (P < 0.001 and P < 0.01 respectively). CONCLUSIONS: The present data extend our understanding of the relationship between follicle dynamics, serum inhibins and FSH during ovarian hyperstimulation. However, although mid follicular inhibin B does correlate with the number of developing follicles, it does not facilitate the identification of women at risk for multiple follicle development.     

Circulating immunoreactive inhibin levels during the normal human menstrual cycle

Serum inhibin concentrations were measured daily by RIA in six normal women throughout one menstrual cycle. The RIA was specific for inhibin, and inhibin subunits and related proteins cross-reacted minimally in it. In the early to midfollicular phase, inhibin levels changed little, while in the late follicular phase, inhibin levels rose, in parallel with estradiol (r = 0.43; P less than 0.05; n = 22), to a peak level of 714 (407-1267) U/L (geometric mean +/- 67% confidence limits) coincident with the midcycle LH and FSH surges. An inverse relationship was found between serum inhibin and FSH during the mid- to late follicular phase (r = 0.42; P less than 0.01; n = 45). Inhibin levels rose further during the luteal phase to a peak level of 1490 (1086-2028) U/L 7-8 days after the LH surge, and they correlated positively with serum progesterone (r = 0.76; P less than 0.001; n = 49) and inversely with serum FSH (r = 0.43; P less than 0.01; n = 49) throughout the luteal phase. We conclude that 1) circulating inhibin is detectable throughout the normal menstrual cycle; 2) in the late follicular phase, inhibin levels rise in parallel with estradiol, consistent with the concept that both are products of the maturing follicle; 3) in the luteal phase, the profile of inhibin suggests that it is a secretory product of the corpus luteum; and 4) the inverse relationship between inhibin and FSH in the follicular phase is consistent with the inhibin hypothesis, while at midcycle there is loss of the inhibitory effect of inhibin on FSH secretion. The inverse relationship between FSH and inhibin during the luteal phase suggests a hitherto unsuspected role for inhibin in the feedback regulation of FSH secretion.     

Is the short follicular phase in older women secondary to advanced or accelerated dominant follicle development?

This study sought to determine whether the shortened follicular phase in ovulatory older women is secondary to advanced (i.e. earlier) or accelerated (i.e. more rapid) folliculogenesis. Normal ovulatory women, aged 40-45 yr (n = 15) and 20-25 yr (n = 13), underwent daily venipuncture and transvaginal ultrasonography throughout the follicular phase of a spontaneous menstrual cycle (control cycle) and after pituitary down-regulation with a GnRH agonist (study cycle). As expected, the older subjects in the control cycles demonstrated an elevated d 3 FSH and a shortened follicular phase compared with the younger subjects. After release from hypothalamic-pituitary-ovarian axis suppression, the early follicular phase FSH peak occurred earlier (6.8 vs. 9.8 d; P < 0.01) and was of a greater magnitude (12.1 vs. 6.5 mIU/ml; P < 0.01) in the older subjects. The time from release of suppression until the subsequent LH surge was also shorter (17.5 vs. 20.8 d; P < 0.01) in the older group. However, the time from FSH peak to LH surge was similar in the older and younger groups (10.7 vs. 11.0 d; P = 0.74). Compared with younger women, older subjects had normal follicular phase levels of estradiol and inhibin A and lower levels of inhibin B in both control and study cycles. We conclude that the shortened follicular phase observed in older ovulatory women is due to earlier dominant follicle selection, independent of hormonal influences from the preceding luteal phase.     

Interrelationships between ovarian and pituitary hormones in ovulatory menstrual cycles across reproductive age

CONTEXT: Ovarian hormones regulate pituitary gonadotropin secretion across the menstrual cycle via negative and positive feedback mechanisms. The contribution of individual hormones is complex and is a continuing area of research. OBJECTIVE: The aim of the study was to identify relationships between LH/FSH and estradiol, progesterone, inhibin A, inhibin B, and anti-Mullerian hormone (AMH) in ovulatory menstrual cycles across reproductive age. DESIGN: Serum ovarian and pituitary hormones were studied in a group of young (<35 yr; n = 21) and older (>45 yr; n = 55) women. The slopes of the regression lines relating the ovarian and pituitary hormones were determined by multiple linear regression analysis and expressed with 95% confidence intervals for each ovarian hormone, with FSH and LH as independent variables. Both simultaneous and delayed (time lagged) relationships were examined. RESULTS: Clear associations were evident for the lagged prediction of FSH, with significant negative associations being evident with inhibin B and AMH in the follicular phase and with estradiol, inhibin B, progesterone, and AMH in the luteal phase. For the lagged prediction of LH, significant positive and negative associations were observed with estradiol and inhibin B, respectively, in the follicular phase and a negative association with progesterone and inhibin B in the luteal phase. CONCLUSIONS: It is concluded that in the follicular phase, inhibin B is a major feedback regulator of FSH and may also be a negative feedback regulator of LH. AMH may be indirectly involved in FSH regulation.     

Differential regulation of inhibin A and inhibin B by luteinizing hormone, follicle-stimulating hormone, and stage of follicle development

Inhibin B and inhibin A exhibit unique patterns of secretion across the follicular phase of the menstrual cycle. To test the hypothesis that the distinct patterns of inhibin B and inhibin A secretion result from differential regulation by LH and FSH, a series of controlled experiments was designed to dissect the specific effects of LH and FSH at distinct stages of follicle development. After GnRH agonist desensitization, women with small antral follicles were treated with recombinant human LH (rhLH), rhFSH, or rhFSH and estradiol (E(2)). rhLH or rhFSH was also administered when follicles reached the preovulatory stage in gonadotropin-stimulated or spontaneous cycles. At the small antral stage of development, rhFSH, but not rhLH, administration increased inhibin B (17.4 +/- 4.6 to 321.0 +/- 97.0 pg/mL; P < 0.05), inhibin A (0.6 +/- 0.1 to 2.6 +/- 0.6 IU/mL; P < 0.05), and E(2) [15.8 +/- 3.6 to 95.3 +/- 26.9 pg/mL (58.0 +/- 13.2 to 349.8 +/- 98.7 pmol/L); P < 0.05]. The inhibin B increase preceded inhibin A by 48 h. Addition of E(2) to FSH resulted in a greater increase in inhibin B (23.2 +/- 6.4 to 865.2 +/- 294.5 pg/mL; P < 0.05) than FSH alone (P < 0.05). At the preovulatory stage, rhLH administration increased inhibin A (15.9 +/- 10.3 to 21.5 +/- 13.7 IU/mL; P < 0.05) and E(2) [669.4 +/- 285.5 to 943.6 +/- 388.1 pg/mL (2457.4 +/- 1048.1 to 3464.0 +/- 1424.7 pmol/L); P < 0.05], but not inhibin B, as did rhFSH administration in spontaneous cycles [E(2): 226.4 +/- 102.7 to 264.7 +/- 121.0 pg/mL (831.1 +/- 377.0 to 971.7 +/- 444.2 pmol/L); P < 0.05; inhibin A: 2.6 +/- 1.3 to 3.7 +/- 1.9 IU/mL; P < 0.05; and inhibin B: 76.3 +/- 32.2 to 77.6 +/- 32.8 pg/mL; P = NS]. These findings suggest that increases in both FSH and E(2) in the early follicular phase result in increased inhibin B secretion at early stages of follicle development, whereas the selective LH rise in the late follicular phase favors inhibin A secretion from more mature follicles. Thus, both differential secretion of LH and FSH and the stage of follicle development determine the patterns of inhibin A and inhibin B secretion in the normal menstrual cycle.     

Circulating inhibins and activin A during GnRH-analogue down-regulation and ovarian hyperstimulation with recombinant FSH for in-vitro fertilization-embryo transfer

OBJECTIVE We have investigated serial changes in plasma concentrations of inhibin A, inhibin B, pro αC and activin A in women undergoing stimulation with recombinant FSH in ‘long-protocol’ down-regulated cycles of IVF treatment. DESIGN Blood samples were collected during the entire IVF treatment cycle at points coinciding with the early follicular phase of the cycle preceding treatment, pituitary down-regulation, stimulation with recombinant FSH, ovulatory triggering, and the luteal phase of the cycle. In patients who achieved conception, blood samples were also taken during the first 2 weeks of pregnancy. All samples were analysed for inhibin A, inhibin B, pro αC, activin A and oestradiol. PATIENTS Fifteen women with normal ovarian function undergoing IVF treatment with tubal factor, mild endometriosis or idiopathic infertility. RESULTS During pituitary desensitization, both inhibin A and inhibin B were significantly (P<0.001, P=0.002, respectively) reduced whereas levels of pro αC and activin A were largely unaltered. Levels of both inhibins rose markedly (P<0.01) during FSH stimulation and a further rise in inhibin A was detected on the day after ovulatory trigger. Levels of both inhibin A and inhibin B then fell during and after oocyte pickup and continued to fall during the luteal phase. Activin A levels rose less markedly during gonadotrophin stimulation. Statistical analysis showed a high degree of correlation between the number of follicles (>10 mm) and serum inhibin A (r=0.65, P<0.01) and pro αC (r=0.65, P<0.01) concentrations during the late follicular phase. CONCLUSIONS These results indicate that ovarian production of dimeric inhibin A and B are gonadotrophin dependent, whereas activin A may have a significant gonadotrophin independent or extra-gonadal source. Inhibin A and pro αC may be useful markers for monitoring the effects of gonadotrophin stimulation.     

Differential regulation of inhibin B and inhibin a by follicle-stimulating hormone and local growth factors in human granulosa cells from small antral follicles

Serum inhibin B rises across the luteal-follicular transition, whereas inhibin A does not increase until the late follicular phase of the menstrual cycle. To test the hypothesis that inhibin B is secreted from preantral and small antral follicles and that FSH and local growth factors differentially regulate inhibin B and inhibin A from these developing follicles, human ovaries were obtained after oophorectomy. Basal secretion of inhibin B and inhibin A was examined in intact preantral follicles in culture (n = 6). Basal secretion and regulation of inhibin B and inhibin A secretion by gonadotropins, androstenedione, activin A, insulin, and IGF-I were examined in cultured granulosa cells from small antral follicles (n = 21). Inhibin B secretion from preantral follicle cultures was detectable at baseline (range, 17-96 pg/mL), whereas inhibin A was not detectable. In contrast, both inhibin B and inhibin A were detectable in granulosa cell cultures from small antral follicles. In granulosa cells from small antral follicles, FSH (30 ng/mL) stimulated inhibin A 3-fold (10.5 +/- 2.2 to 32.5 +/- 8.3 IU/mL; P < 0.001), but not inhibin B secretion (1730 +/- 354 to 2314 +/- 532 pg/mL; P = NS). Likewise, cAMP (1 mmol/L) stimulated inhibin A 4-fold (16.6 +/- 4.3 to 62.5 +/- 21.9 IU/mL; P < 0.002), but not inhibin B secretion (2327 +/- 546 to 1877 +/- 377 pg/mL; P = NS). hCG (30 ng/mL) did not stimulate inhibin A or inhibin B. Androstenedione (10(-)(7) mol/L), activin (30 ng/mL), insulin (30 ng/mL), and insulin-like growth factor I (IGF-I; 100 ng/mL) alone did not stimulate inhibin A or inhibin B secretion. Further, FSH-stimulated inhibin A secretion was not augmented by androstenedione, activin, insulin, or IGF-I. In contrast, the combination of IGF-I and FSH was the only treatment that stimulated inhibin B secretion (1742 +/- 380 to 2881 +/- 731 pg/mL; P < 0.03). However, FSH in combination with IGF-I resulted in greater stimulation of inhibin A (340%) than inhibin B (65%). These findings demonstrate that inhibin B is secreted from developing preantral and small antral follicles, but is not directly stimulated by FSH. However, the combination of FSH and IGF-I enhanced inhibin B secretion. In contrast, inhibin A is not secreted from preantral follicles, but in small antral follicles FSH and cAMP stimulate inhibin A secretion. Further, FSH in combination with IGF-I results in a greater degree of stimulation of inhibin A than of inhibin B. These findings suggest that FSH and IGF-I differentially regulate inhibin A and inhibin B secretion. However, additional growth factors or increasing granulosa cell number may contribute to the preferential serum inhibin B increase across the luteal-follicular transition in the menstrual cycle.     

Inhibin concentrations throughout the menstrual cycles of normal, infertile, and older women compared with those during spontaneous conception cycles

Plasma immunoreactive inhibin levels have been measured in a series of normal conception cycles (group I; n = 7), and the data compared to inhibin concentrations in normal menstrual cycles (group II; n = 8), in women with luteal phase defects (group III; n = 7), and in women in the perimenopausal period (group IV; n = 6). Daily plasma levels of LH, FSH, progesterone, estradiol, and inhibin were determined in each subject, and daily mean profiles for each hormone in each subject group were calculated and expressed as geometric means with 68% confidence limits. During the follicular and early luteal phases, inhibin concentrations in the normal nonpregnant group (group II) were significantly higher than those in the conception cycles of group I, but after implantation in the conception cycles, inhibin concentrations increased to levels in excess of those seen at any time in nonconception cycles (716-1352 U/L; P less than 0.02). The postimplantation rise in inhibin did not initially appear to follow the same pattern as progesterone. While progesterone concentrations rose within 24 h of the first detectable increase in hCG, inhibin levels did not increase until 3 days later, although after this point concentrations increased serially and in parallel with progesterone. LH and FSH concentrations were markedly suppressed after implantation. Follicular and early luteal inhibin concentrations in cycles with luteal phase defects were also higher than those in conception cycles, although this difference was only significant in the midfollicular phase. Follicular phase inhibin concentrations in cycles from older women (group IV) were lower than those in groups II and III, but were not distinguishable from those in the conception cycles. Estradiol concentrations in the same subjects were significantly lower during the early follicular phase, while follicular and luteal FSH concentrations were significantly higher than those during conception cycles. Finally, examination of the relationship between inhibin, FSH, and estradiol around menstruation in the older women revealed a far closer temporal association between FSH and estradiol than between FSH and inhibin. In conclusion, inhibin concentrations rise and fall throughout the human menstrual cycle in a manner that is similar to but at specific times significantly different from that of either of the ovarian steroids estradiol and progesterone. It is considered to be a peptide of granulosa cell origin and may be an indicator of the size of the follicular pool during the early stage of the cycle. However, although there is some degree of inverse correlation between profiles of inhibin and profiles of FSH, this relationship is not particularly clear.(ABSTRACT TRUNCATED AT 400 WORDS)     

Comparison of follicle-stimulating-hormone-stimulated dimeric inhibin and estradiol responses as indicators of granulosa cell function in polycystic ovary syndrome and normal women

CONTEXT: Follicular phase secretion of inhibin B, like that of estradiol (E(2)), correlates with the quantity and quality of developing follicles. However, it has not been established whether inhibin B responses to gonadotropin stimulation parallel those of E(2) as a reflection of granulosa cell functional capacity. OBJECTIVE: Our objective was to determine whether inhibin B responses to FSH stimulation are similar to those of E(2) in women with polycystic ovary syndrome (PCOS) and normal women. DESIGN AND SETTING: We conducted a prospective study to compare ovarian responses in two groups of women at a general clinical research center in a tertiary academic medical center. PATIENTS: Women with PCOS, 18-35 yr (n = 19), and normal ovulatory controls, 18-35 yr (n = 7), were recruited for study. INTERVENTIONS: Serum samples were measured over a 24-h period after an iv injection of recombinant human FSH, 150 IU. MAIN OUTCOME MEASURES: Serum E(2), inhibin A, and inhibin B responses after FSH administration were assessed. RESULTS: In PCOS women, the 24-h production of inhibin B and E(2) after FSH was significantly greater than that of normal controls. Within the PCOS group, the fold change in inhibin B was significantly greater than that of E(2). Inhibin A responses between groups were similar and of markedly lower magnitude. CONCLUSIONS: FSH-stimulated inhibin B responses may be employed to assess the functional capacity of granulosa cells in PCOS and normal women.     

Gonadotropins, prolactin, inhibin A, inhibin B, and activin A in human fetal serum from midpregnancy and term pregnancy

Using specific enzyme-linked immunosorbent assays we measured inhibin A, inhibin B, and activin A in relation to LH, FSH, and PRL in normal human fetal midpregnancy serum obtained by in utero cord venipuncture (n = 25) and compared these results to those in fetal serum from term pregnancies (n = 23). We also tested serum from fetuses with intrauterine growth retardation (n = 6) or trisomy 21 (n = 6). We found no measurable inhibin A, except in three midpregnancy males (3 of 14). Inhibin B, however, was detected in midpregnancy male fetuses (167+/-67 pg/mL) and was higher than that in females (16+/-12 pg/mL). It was present in male term fetuses (125+/-32 pg/mL), but not in females. The activin A levels did not significantly differ between term and midpregnancy males and females. LH and FSH were detected in midpregnancy male fetuses (4.4+/-3.3 and 0.77+/-0.49 mIU/mL, respectively), with higher levels in females (33.0+/-23.2 and 54.4+/-27.7 mIU/mL, respectively), and were suppressed at term. PRL did not exhibit sexual difference, but showed a higher level at term (322.4+/-113.8 ng/mL) than at midpregnancy (33.0+/-26.1 ng/mL). Comparison of inhibin B with FSH levels showed correlation coefficients of -0.565 at midpregnancy vs. +0.445 at term. Serum from fetuses with intrauterine growth retardation or trisomy 21 did not show any different hormonal profiles. These data suggest that inhibin B is probably an additional factor in FSH inhibition at midpregnancy, whereas activin A is not associated with any change in the different studied populations. We speculate that inhibin A could be a method to detect maternal blood contamination in cord venipuncture.     

Follicle-stimulating hormone-inhibin B interactions during the follicular phase of the primate menstrual cycle revealed by gonadotropin-releasing hormone antagonist and antiestrogen treatment

The aim was to determine the pattern of inhibin A and inhibin B secretion during the ovulatory cycle of the macaque and to explore the effects of manipulating follicular phase FSH on inhibin B secretion by: 1) blocking the early follicular phase rise in FSH with GnRH antagonist treatment; 2) administering FSH in GnRH antagonist-treated animals; and 3) preventing the midfollicular phase decline in FSH by a specific antiestrogen. Treatment with GnRH antagonist, starting on day 25 of the cycle, abolished the early follicular phase rise in FSH and the associated increase in inhibin B. The same treatment, followed by exogenous FSH, restored the secretion of inhibin B. Treatment with antiestrogen, commencing during the midfollicular phase, induced a supraphysiological rise in FSH, followed by a marked stimulation of inhibin B and estradiol secretion. Despite continued antiestrogen treatment, FSH secretion declined before peak values of inhibin B and estradiol were attained, implying a potential endocrine role for inhibin B, in addition to estradiol, in the negative feedback regulation of FSH. These results show that follicular phase FSH is the major stimulus for inhibin B secretion.     

Selective theca cell dysfunction in autoimmune oophoritis results in multifollicular development, decreased estradiol, and elevated inhibin B levels

We describe the clinical course of three women with presumptive autoimmune oophoritis who developed multiple follicles but very low to undetectable estradiol levels. Multiple follicles developed spontaneously in all subjects and during pulsatile GnRH treatment for ovulation induction in subject 1. The development of multiple dominant follicles was accompanied by LH levels in the postmenopausal range and FSH levels at the upper limit for premenopausal women. Serum inhibin B levels were elevated appropriately in the setting of multifollicular development, but estradiol levels remained low. Measurement of estradiol precursors demonstrated androstenedione and estrone levels below the 95th percentile in normal women. Adrenal cortical antibodies, and antibodies to 21-hydroxylase and P450 side chain cleavage enzymes were identified in all subjects. All subjects met the criteria for premature ovarian failure during follow-up. Subject 1 later developed adrenal failure, whereas subject 3 had adrenal failure at the time of the study. These subjects elucidate the hormonal pattern in autoimmune oophoritis, before the full criteria for premature ovarian failure are met. The elevated inhibin A and B levels, which accompany the development of multiple small and dominant follicles in these women, suppress FSH relative to LH levels, virtually independent of estradiol. These data provide further evidence for an important role of inhibin B and inhibin A in the negative feedback control of FSH. In addition, the normal inhibin A and inhibin B production in the absence of estradiol precursors and estradiol provide insight into the selective dysfunction of the theca cells in autoimmune oophoritis.     

Relationship of estradiol and inhibin to the follicle-stimulating hormone variability in hypergonadotropic hypogonadism or premature ovarian failure

Recent studies have demonstrated the presence of ovarian follicular development in up to 78% of women with premature ovarian failure (POF). The purpose of this study was to examine the control of FSH by estradiol and inhibin secretion from these follicles. Weekly blood samples were collected in conjunction with assessment of ovarian follicle development by ultrasound for at least 12 wk in 49 subjects with POF. Results were compared with those of 44 normal cycling women. Ovulatory cycles occurred in 24 subjects (49%) with POF. These ovulatory cycles were characterized by higher FSH and lower inhibin B and inhibin A levels, whereas estradiol levels were higher compared with those in normal women. Follicles developed in the absence of ovulation in 18 women (37%) with POF, whereas the ovaries were inactive in seven women (14%). FSH levels were lower in POF women with ovulatory or anovulatory follicle development compared with levels in women with inactive ovaries. These findings demonstrate that ovulatory cycles in women with POF are characterized by a persistent elevation in FSH compared with levels in normal cycling women. The association of increased FSH with lower levels of inhibin B and inhibin A, but higher estradiol levels provides additional evidence for an important physiological role of the inhibins in the negative feedback control of FSH. These data also demonstrate the variability in FSH levels as a function of underlying follicular development in women with POF.     

Inverse correlation between baseline inhibin B and FSH after stimulation with GnRH: a study of serum levels of inhibin A and B, pro alpha-C and activin A in women with ovulatory disturbances before and after stimulation with GnRH

OBJECTIVE: Interest has focused recently on the influences of the polypeptide factors inhibin and activin on the selective regulation of the pituitary secretion of gonadotropins. DESIGN: Measurement of the concentrations of inhibin-related proteins in relation to the changes in pituitary gonadotropin (FSH, LH) parameters, after GnRH stimulation with a bolus injection of 100 microg gonadorelin, in 19 women with ovulatory disturbances. METHODS: Serum levels of inhibin A and B, activin A, and pro alpha-C were measured using sensitive ELISA kits. RESULTS: Within 60 min after GnRH stimulation, FSH values doubled from 5 to 10 mU/ml (P < 0.001). LH increased 12-fold from 2 to 24 mU/ml (P < 0.001). Activin A showed a significant decrease from 0.47 to 0.36 ng/ml (P < 0.001), whereas pro alpha-C increased from 127 to 156 pg/ml (P = 0.039). The median inhibin A concentration did not show a significant change between baseline and the 60 min value, whereas inhibin B was characterized by a minor, but not significant, increase in the median from 168 to 179 pg/ml (P = 0.408). A significant inverse correlation (P = 0.014) with a mean coefficient of correlation of 0.5516 was found, demonstrating a strong relationship between high inhibin B baseline levels and a small increase of FSH after 60 min. CONCLUSION: Our results show an interesting correlation between the baseline inhibin B and the change in FSH before and after GnRH stimulation. A high baseline inhibin B implies only a minor increase of FSH after 60 min.     

Evidence of early ovarian aging in fragile X premutation carriers

Up to 28% of female fragile X premutation carriers develop premature ovarian failure. To test the hypothesis that fragile X premutation carriers with ovulatory menstrual cycles exhibit hormone changes characteristic of early ovarian aging, 11 regularly cycling fragile X premutation carriers, 24-41 yr old (34.5 +/- 5.7 yr, mean +/- sd), drew daily blood samples across one menstrual cycle. LH, FSH, estradiol, progesterone (P4), inhibin A, and inhibin B levels were compared with levels in 22 age-matched, regularly cycling women, 23-41 yr old (34.6 +/- 5.8 yr), at each cycle stage.Total cycle (26.1 +/- 1.0 vs. 28.2 +/- 0.4 d; P < 0.05) and follicular phase length (12.9 +/- 0.8 vs. 14.5 +/- 0.4 d; P < 0.05) were decreased in fragile X premutation carriers compared with age-matched controls, whereas luteal phase length was similar (13.2 +/- 0.5 vs. 13.7 +/- 0.3 d; P = not significant). FSH was elevated across the follicular (21.9 +/- 3.5 vs. 11.2 +/- 0.5 IU/liter; P < 0.001) and luteal phases (14.6 +/- 3.9 vs. 7.9 +/- 0.5 IU/liter; P < 0.05) in fragile X premutation carriers compared with age-matched controls. Inhibin B in the follicular phase (77 +/- 11 vs. 104 +/- 6 pg/ml; P < 0.05) and inhibin A (3.4 +/- 0.7 vs. 5.8 +/- 0.5 IU/ml; P < 0.01) and P4 [7.3 +/- 1.0 vs. 10.1 +/- 0.7 ng/ml (23.2 +/- 3.0 vs. 32.1 +/- 2.3 nmol/liter); P < 0.05] in the luteal phase were decreased in fragile X premutation carriers compared with age-matched controls, whereas there was no difference in estradiol or LH.In summary, despite regular ovulatory cycles, FSH was increased in fragile X premutation carriers compared with age-matched controls. The increased FSH was accompanied by decreased inhibin B in the follicular phase and inhibin A and P4 in the luteal phase. These hormonal changes suggest that fragile X premutation carriers exhibit early ovarian aging despite regular menstrual cycles. Early ovarian aging in fragile X premutation carriers likely results from decreased follicle number and function, as reflected by lower inhibin B, inhibin A, and P4 levels.     

Activin and inhibin receptor gene expression in the ewe pituitary throughout the oestrous cycle

In mammals, activin and inhibin are important regulators of FSH secretion. Previous studies have demonstrated that primary ovine pituitary cells express different activin receptor subtypes: activin receptor-like (ALK)2, ALK4, activin type II receptor A (ActRIIA), ActRIIB and Smad proteins in vitro. Here, we have carried out physiological studies to investigate the pattern of mRNA expression of the activin receptor subunits in the ewe pituitary throughout the oestrous cycle. The oestrous cycles of ewes were synchronized with progestagen sponges. The animals were killed 36 h (before the preovulatory surge, n=4), 48 h (during the preovulatory surge, n=4), 72 h (during the second surge of FSH, n=6) and 192 h (during the luteal phase, n=4) after sponge removal. Using Northern blots, we have shown that the levels of ALK2, ALK4 and ActRIIB mRNA were significantly higher before the preovulatory surge and during the secondary surge of FSH as compared with both during the preovulatory surge and the luteal phase, whereas the level of the ActRIIA mRNA was similar throughout the oestrous cycle. Using Western blots we have also demonstrated that the level of phospho-Smad2 did not vary during the reproductive cycle. Inhibin binding protein (InhBP/p120) and the transforming growth factor-beta type III receptor, betaglycan, have been identified as putative inhibin co-receptors. In this study, we cloned a fragment of both InhBP/p120 and betaglycan cDNAs in the ewe and showed by Northern blot that pituitary betaglycan and InhBP/p120 mRNA levels did not fluctuate across the oestrous cycle nor did they correlate with serum FSH levels.     

Secretion of inhibin A, inhibin B and inhibin pro-alphaC during the oestrous cycle of the golden hamster (Mesocricetus auratus).

Plasma concentrations of inhibin pro-alphaC, inhibin A and inhibin B were determined by enzyme-linked immunosorbent assay at 6 h intervals throughout the 4-day oestrous cycle of the golden hamster. Plasma concentrations of follicle-stimulating hormone (FSH) and oestradiol-17beta were also measured by radioimmunoassay during the oestrous cycle. Plasma concentrations of inhibin A increased from the early morning of day 1 (day 1=day of ovulation) and reached plateau levels at 0500 h on day 2. An abrupt increase in plasma concentrations of inhibin A was found at 1700 h on day 4, when the preovulatory FSH surge was observed. An increase in plasma concentrations of inhibin B occurred on day 1 and reached plateau levels at 1700 h on day 1. The levels remained elevated until 0500 h on day 4 and declined gradually by 2300 h on day 4. Plasma concentrations of inhibin pro-alphaC gradually increased with some fluctuation from day 1 to 1700 h on day 4 and then declined. Significant negative relationships were noted between plasma FSH and both dimeric forms of inhibin from day 1 to day 3. Significant positive relationships were found between plasma oestradiol-17beta and inhibin A or inhibin pro-alphaC throughout the oestrous cycle. In contrast, no significant relationship was found between plasma oestradiol-17beta and inhibin B. These findings suggest that both dimeric forms of inhibin play a role in the regulation of FSH secretion during follicular development. These findings also suggest that inhibin pro-alphaC could be secreted primarily by large follicles, and early atretic follicles could also be responsible for inhibin pro-alphaC secretion. On the other hand, the secretory pattern of dimeric inhibins might shift from inhibin B to inhibin A with follicular development.