Immunoreactive Inhibin Levels Research Articles

Circulating Testosterone and Inhibin Levels at Different Ages in the Male Beluga (<i>Delphinapterus leucas</i>)

This study is the first report on circulating testosterone and inhibin levels in a species of whales, the beluga. Circulating testosterone and immunoreactive (ir-) inhibin levels in two captive male belugas ("Nack", originally from Canada and "Duke", from the Okhotsk Sea) were measured every month for 9 years between 1995 and 2003. Assuming that clearly increased testosterone levels in the circulation indicates that the belugas had reached sexual maturity, at the ages of 10 ("Nack") and 11 years old ("Duke"). Their testosterone levels before the significant increase (pre-pubertal) were 0.42 ± 0.07 ng/ml (n=18) and 0.35 ± 0.10 ng/ml (n=18) and, those of after the increase (maturity) were 1.65 ± 0.14 ng/m l (n=74) and 2.06 ± 0.14 ng/ml (n=74). Circulating ir-inhibin levels before sexual maturity were 0.78 ± 0.04 ng/ml (n=18) and 0.64 ± 0.04 ng/ml (n=15) and, after sexual maturity were 0.52 ± 0.02 ng/ml (n=56) and 0.43 ± 0.02 ng/ml (n=67). Seasonal changes were observed in the testosterone levels after sexual maturity and the levels increased during March and April in Canadian origin "Nack", and peaked in February in Okhotsk origin "Duke". Circulating ir-inhibin level gradually decreased as they aged. A negative correlation between the circulating testosterone and ir-inhibin was observed. No seasonal changes were observed in the ir-inhibin levels after sexual maturity. These data will surely correspond to clarification of endocrinology and the successful reproduction of the beluga.

Secretory Pattern of Inhibin During Estrous Cycle and Pregnancy in African (Loxodonta africana) and Asian (Elephas maximus) Elephants

The ovary of female elephants has multiple corpora lutea (CL) during the estrous cycle and gestation. The previous reports clearly demonstrated that inhibin was secreted from lutein cells as well as granulosa cells of antral follicles in cyclic Asian elephants. The aim of this study is to investigate the inhibin secretion during the pregnancy in African and Asian elephants. Two African elephants and two Asian elephants were subjected to this study. Circulating levels of immunoreactive (ir-) inhibin and progesterone were measured by radioimmunoassay. Four pregnant periods of an African elephant and three pregnant periods of an Asian elephant were analyzed in this study. Circulating levels of ir-inhibin started to increase at 1 or 2 week before the ovulation and reached the peak level 3 or 4 weeks earlier than progesterone during the estrous cycle in both African and Asian elephants. After last luteal phase, the serum levels of ir-inhibin remained low throughout pregnancy in both an African and an Asian elephant. The mean levels of ir-inhibin during the pregnancy were lower than the luteal phase in the estrous cycle despite high progesterone levels were maintained throughout the pregnancy. These results strongly suggest that CL secrete a large amount of progesterone but not inhibin during the pregnancy in elephants.

Ovarian Follicular Dynamics and Hormonal Changes in Goats during Early Pregnancy

The present study was conducted to characterize follicular development and its hormonal control during early pregnancy in goats. The ovaries of goats (n=8) were scanned daily for follicles (> or = 2 mm in diameter) and corpora lutea by transrectal ultrasound with blood sampling from the jugular vein for monitoring the hormonal changes during the first thirty-five days after mating. During early pregnancy, three (37.5%), four (50%) and one (12.5%) goat showed nine, eight and seven waves of follicular development, respectively. The corpora lutea were detected as early as Day 3.61 ± 0.45 (7.47 ± 0.43 mm) of pregnancy (Day 0=day of mating) and attained their maximal cross-sectional diameter (10.64 ± 0.37 mm) on Day 25.7 ± 0.8 of pregnancy, respectively. A transient rise in FSH levels was temporally associated with the day of follicular wave emergence (up to three days prior to wave emergence). The plasma LH and estradiol levels were negatively correlated with the progesterone concentration. The rise in plasma immunoreactive (ir) inhibin levels was negatively correlated with the FSH concentration and positively correlated with the number of large-sized follicles. Alternatively, the mean plasma ir-inhibin levels showed a noticeable decline with the progression of pregnancy. The present results demonstrated that follicular development during early pregnancy shows a wave-like pattern, with seven to nine waves developing until Day 35 after breeding, and that the number of follicular waves can be predicted by the number of FSH peaks. The current study also demonstrated that the role of inhibin as an FSH regulator is maintained throughout early pregnancy.

Change in Circulating Follicle-Stimulating Hormone, Luteinizing Hormone, Immunoreactive Inhibin, Progesterone, Testosterone and Estradiol-17.BETA. in Fillies from Birth to 6 Months of Age

The relationship among circulating levels of follicle-stimulating hormone (FSH), luteinizing hormone (LH), immunoreactive (ir) inhibin, progesterone, testosterone and estradiol-17β were investigated in fillies from birth to 6 months of age. Six hundred ninety-four Thoroughbred female foals were used for evaluating the changes in these hormones. Blood samples were collected by jugular venipuncture for hormonal assays. The results show that after birth, progesterone, testosterone and estradiol-17β levels rapidly drop within 48 hr, and remain at this lower level until six months of age. On the other hand, plasma concentrations of ir-inhibin begin to decrease at 3 days after birth, falling by more than half in the first 20 days after birth, and then continue to slowly decline until six months of age. Circulating levels of FSH show a small increase within 48 hr after birth, then decline to the lowest levels at 30 days after birth, followed by a rise to more or less stable levels at six months of age, whereas LH concentrations rapidly decrease after birth, dropping to a lower level at 10 days after birth, then remain at the lower value until six months of age. These results demonstrate that, after birth, in a filly, there is a notable decline in steroid hormones which then remain at these relatively stable lower levels until six months of age. The steady increase in basal FSH negatively correlates with the decline in circulating inhibin. This slow increase in the basal levels of FSH may stimulate follicular development during the early stages of puberty in a filly.

Effect of a Single Injection of Human Chorionic Gonadotropin (hCG) on Testicular Hormones and Gonadotropins in the Thoroughbred Stallion

The changes in testicular and pituitary functions in response to human chorionic gonadotropin (hCG) in the breeding and non-breeding season were investigated and compared in the Thoroughbred stallion. Five mature Thoroughbred stallions ranging in ages from 7 to 21 years were injected in May (breeding season) and October (non-breeding season). All animals received an intramuscular injection of 5,000 IU hCG in the experiments. Peripheral blood samples were collected in heparinized tubes from the jugular vein for hormonal assays just before the injection (Day 0) and at a daily interval for five days following the injections (Days 1, 2, 3, 4 and 5). Basal levels of immunoreactive (ir) inhibin, testosterone, estradiol-17β, FSH and LH were higher in the breeding season than in the non-breeding season. There were significant differences in estradiol-17β, FSH and LH between the two seasons. Ir-inhibin exhibited significant increases on Day 2 after the hCG treatment in the non-breeding season, though there was no change in the breeding season. Plasma levels of testosterone showed remarkable increases after the hCG injection in both seasons. The peak levels of plasma testosterone were observed on Days 2 and 3 in the breeding and non-breeding seasons. Plasma estradiol-17β was significantly higher than the basal level on Day 3 in the non-breeding season, whereas there was no change in the breeding season. Plasma levels of FSH declined from Day 1 to Day 3, then recovered to the basal level (Day 0) on Day 4 after hCG treatment in the breeding season, whereas there was no change in the non-breeding season. Circulating LH showed a significant decrease on Day 3 compared to the based level in the breeding season, but no significant change in the non-breeding season after a treatment of hCG. A significant negative correlation was observed between testosterone and FSH in the breeding season. In conclusion, hCG treatment stimulates secretion of testicular hormones and these testicular hormones temporarily suppress secretion of gonadotropins from the pituitary gland. These results also suggested that Leydig cells of thoroughbred stallion testes have LH receptors in the non-breeding season, the same as in the breeding season.

Ovarian follicular differentiation with prepubertal gonadotropin surges and gonadotropin priming in mice

Preantral follicles were mechanically isolated from the ovaries of 1.5 to 8 week old mice and cultured in vitro for 4 days in the presence or absence of either activin A or FSH. Plasma gonadotropin, estradiol and immunoreactive (IR) inhibin levels were measured. Cultured follicles showed stepwise changes in response to recombinant human (rh) FSH, with no response until 11 days, a gradual increase from 2 weeks, culminating in a strong response to rhFSH at 8 weeks. The response to activin A was vice versa. It enhanced the effect of rhFSH on preantral follicular growth of up to 4-week-old mice, but inhibited the effect of rhFSH in 8-week-old mice. The peak of the prepubertal gonadotropin surge was observed on day 11. Seven-day-old mice were treated with either luteinizing hormone releasing hormone (LHRH) or rhFSH or human chorionic gonadotropin (hCG) for 3 consecutive days from day 7, and follicles were collected on day 11. Those follicles showed enhanced response to rhFSH, no response to activin A, and an enhanced response to the combination of rhFSH and activin A, suggesting that the chronological changes in follicular response are a result of the prepubertal gonadotropin surge.

Gonadal malignant germ cell tumors express immunoreactive inhibin/activin subunits.

Inhibin and activin are proteins produced by ovarian granulosa cells and testicular Sertoli cells and are members of the transforming growth factor-beta superfamily. Since increased circulating levels of immunoreactive inhibin were detected in women with malignant ovarian tumors, they were proposed as tumor markers for ovarian carcinoma. Immunohistochemical studies later confirmed the presence of inhibin and activin subunits in granulosa cell tumors and epithelial ovarian cancer, as well as in Sertoli and Leydig cell testicular cancer. However, there is discrepant information on the detection of inhibin and activin in malignant germ cell tumors (MGCT). The aim of the present study was to evaluate the immunohistochemical expression of the inhibin/activin alpha, betaA and betaB subunits in ovarian and testicular MGCT specimens using polyclonal antisera. The ovarian tissue samples were composed of 19 MGCT, including dysgerminoma (n=18) and yolk sac tumor (n=1). The testis specimens included classic seminomas (n=20), embryonal carcinomas (n=7), choriocarcinomas (n=2), and yolk sac tumor (n=1). Ovarian and testicular malignant germ cell tumors expressed positive staining for inhibin/activin alpha, betaA and betaB subunits, with some variations between and within individual tumors: while ovarian dysgerminomas were diffusely positive for alpha, betaA and betaB, testicular tumors expressed alpha and betaB subunits, whereas betaA staining was weak. The present results show positive staining for inhibin/activin subunits in ovarian and testicular MGCT, suggesting a possible role in tumorigenesis with the resultant clinical implication.

Regulation of follicle-stimulating hormone secretion by estradiol and dimeric inhibins in the infantile female rat.

Plasma and ovarian levels of the dimeric forms of inhibin and plasma estradiol-17beta were investigated and compared with changes in plasma gonadotropins from Postnatal Day (PND) 5 to PND 30 in the female rat. The inhibin subunit proteins were localized in follicular granulosa cells of the ovary. Plasma immunoreactive inhibin levels were low until PND 15 and increased thereafter. Plasma levels of inhibin B (alpha and beta(B) subunits) remained very low until PND 15 and then increased by approximately 24-fold. In contrast, plasma levels of inhibin A (alpha and beta(A) subunits) were relatively low and steady until PND 20, then increased by approximately 3-fold at PND 25. Changes in ovarian inhibin A and B levels closely resembled those in plasma levels. Plasma FSH levels were low at PND 10 but started to peak from PND 15 and remained high until PND 20, followed by a remarkable reduction at PNDs 25 and 30. This dramatic fall in FSH coincided with the rise of inhibin A. A significant inverse correlation was observed between plasma FSH and plasma inhibin A (r = -0.67, P < 0.0002), ovarian inhibin A (r = -0.48, P < 0.01), plasma inhibin B (r = -0.48, P < 0.05), and ovarian inhibin B (r = -0.54, P < 0.01). Plasma estradiol-17beta levels were elevated from PND 5 through PND 15, then fell sharply through PND 30. Plasma estradiol-17beta was significantly and positively (r = 0.75, P < 0.0002) correlated with plasma FSH. Plasma LH rose to higher levels at PND 15 and tended to be lower thereafter. The inhibin alpha, beta(A), and beta(B) subunits were localized to primary, secondary, and antral and large antral follicles, but the types of these immunopositive follicles varied with age. It appeared that, at PND 25 and afterward, all three subunits were mainly confined to large antral follicles in the ovary. We conclude that estradiol-17beta likely is the major candidate in stimulation of FSH secretion in the infantile female rat. We also conclude that inhibin regulation of pituitary FSH secretion through its negative feedback in the infantile female rat begins to operate after PND 20. We suggest that this negative feedback is achieved by increases in plasma levels of the two dimeric forms, and that inhibin A appears to be the major physiological regulator of FSH secretion at the initiation of this mechanism. We also conclude that large antral follicles in the ovary are the primary source of these bioactive inhibins that are secreted in large amounts into the circulation after PND 20.

Elevated levels of inhibin-A and immunoreactive inhibin in aged male Wistar rats with testicular Leydig cell tumor.

This study was undertaken to investigate the endocrine changes that occur in male Tig:Wistar rats with Leydig cell tumors, with special reference to immunoreactive inhibin (ir-inhibin) and its dimeric forms. Adult male rats from 2 to 28 months of age were used. Blood samples were taken to measure plasma concentrations of ir-inhibin, inhibin-A, inhibin-B, 17beta-estradiol (E2), testosterone, luteinizing hormone (LH), and follicle-stimulating hormone (FSH). Inhibin bioactivity in both peripheral plasma and testicular extracts was also measured. Rats aged 18 months and older had testicular Leydig cell tumor. Testicular tissue sections from 27-month-old rats examined immunohistochemically showed strong positive staining for all 3 inhibin subunits, in particular inhibin alpha and betaA subunits, in the tumor cells. Plasma concentrations of ir-inhibin began to rise significantly (P < .05) at 18 months of age. High bioactivity of inhibin was detected not only in testicular extracts but also in peripheral plasma of aged rats. Thus, plasma concentrations of bioactive inhibin-A, but not inhibin-B, were significantly elevated with increasing age. The concentrations were significantly higher than those in normal male (P < .01) or normal female (P < .05) rats. Plasma concentrations of E2 were significantly (P < .05) elevated only at 23-24 months of age. A marked reduction (P < .05 to .001) in plasma LH and FSH concentrations was observed at 18 months of age and older. Plasma concentrations of testosterone were highest at 2 months of age and then decreased gradually and significantly (P < .05 to .001) afterward. Significant (P < .05 to .001) positive (testosterone vs LH) and negative (ir-inhibin vs FSH, ir-inhibin vs LH, and E2 vs FSH) correlations were observed. It is suggested that plasma inhibin-A levels are elevated in male Tig:Wistar rats with Leydig cell tumor, and thus inhibin-A may be used as a specific marker of testicular Leydig cell tumors. The present results also suggest that the age-related decline in plasma gonadotropins and thus testosterone levels in Tig:Wistar rats may be due to the development of tumors of the Leydig cells rather than to aging per se.

The inhibins and ovarian cancer

Interest in inhibin as a marker of ovarian malignancy was stimulated by the description of elevated immunoreactive inhibin levels in the sera of patients with granulosa cell tumours. Several groups have confirmed the value of serum inhibin in the diagnosis and follow-up of patients with this uncommon malignancy. Immunoreactive inhibin levels are also frequently elevated in patients with mucinous cystadenocarcinoma and less frequently in other forms of ovarian tumour. Assay of sera using the specific dimeric inhibin assays has shown that ovarian tumours are able to secrete dimeric inhibin particularly inhibin B. The less specific α-subunit directed assays, however, most frequently show elevated concentrations. Used in combination with CA125 as a dual tumour marker, it appears in principle that inhibin can be a useful diagnostic agent. Immunohistochemistry for the inhibin subunits has been reported with increasing frequency as a helpful method to assess suspected ovarian stromal cell tumours. Its diagnostic accuracy for other types of ovarian adenocarcinoma appears less reliable. Expression of the inhibin subunit mRNAs has been demonstrated in a variety of ovarian malignancies. The observation that inhibin levels are elevated in ovarian cancer has stimulated studies of their relevance to the molecular pathogenesis of these malignancies. Findings to date have been largely negative with no evidence for activating mutations of the FSH receptor or of the post-receptor signalling pathway proteins.

Production and endocrine role of inhibin during the early development of bull calves.

This study investigated the ontogeny of control of FSH secretion by inhibin during early prepubertal development of bulls by 1) measurements of circulating levels of inhibin and FSH from 1 to 13 wk of age, and 2) immunoneutralization of endogenous inhibin at 7, 21, 60, and 120 days of age. In addition, production and localization of inhibin in testes were examined by immunohistochemistry and Western blots at 7, 21, 60, and 120 days of age. Plasma immunoreactive inhibin levels were relatively low between 1 and 3 wk of age and then showed a tendency to rise (P < 0.1) from 4 wk of age. Circulating concentrations of FSH were low during 3 wk after birth and increased at 5 wk, remained high (P < 0.05) until 16 wk of age. Treatment with inhibin antiserum resulted in a significant (P < 0.05) increase in plasma FSH at 7, 21, 60, and 120 days of age compared to those following injection of control serum; however, the magnitude of the FSH rise after inhibin immunization was greater as bulls aged. There were no significant changes in plasma LH after inhibin immunization. An intense staining of inhibin alpha subunits was found in Sertoli cells within the solid seminiferous cords from 7 to 120 days of age, while no specific immune reaction was found in interstitial cells. Western blot analysis of testicular homogenates isolated from bulls 7-120 days of age revealed presence of a 28.5-kDa molecule that cross-reacted with inhibin alpha subunit and beta(B) subunit-specific antibodies. In this study, before 13 wk of age in bull calves, there was no inverse relationship between plasma concentrations of immunoreactive inhibin and FSH. However, the present immunization study clearly indicates that inhibin participates in the regulation of FSH secretion from infancy to early prepubertal stage, although the endocrine significance of inhibin becomes greater in older bulls. The results also indicate that the major production site of inhibin in the testis is Sertoli cells and that these cells produce inhibin that exerts a negative feedback effect on FSH secretion from early stages of development.

Ovarian tumorigenesis in mice transgenic for murine inhibin alpha subunit promoter-driven Simian Virus 40 T-antigen: ontogeny, functional characteristics, and endocrine effects.

We previously reported formation of ovarian granulosa cell tumors with 100% penetration in a transgenic mouse model with murine inhibin alpha subunit promoter-driven (inhalpha)/Simian Virus 40 T-antigen (Tag). The tumor-bearing inhalpha/Tag mice showed highly elevated serum levels of immunoreactive inhibin. To investigate the onset of tumorigenesis and related endocrine consequences, 6-8 female mice of two inhalpha/Tag lines and their mating control littermates were killed monthly between 1 and 6 mo of age. We also investigated tumorigenesis-related fertility aspects of these two mouse lines. The ontogeny and progression of tumors could be monitored in both inhalpha/Tag lines by alterations of ovarian weights and serum hormone levels. Serum progesterone levels increased in both inhalpha/Tag lines in an age-dependent manner as ovarian tumorigenesis progressed, and a reciprocal decrease occurred in serum LH and FSH. Neither serum estradiol (E(2)) nor uterine weights were significantly altered during tumorigenesis, suggesting that the ovarian tumors represented late stages of granulosa cell differentiation. In conclusion, the present findings show in the inhalpha/Tag TG mice a relation between endocrine consequences of granulosa cell tumorigenesis, and a connection of onset of tumor formation with aberrant steroidogenesis and gonadotropin secretion. These findings indicate that tumors are endocrinologically active and able to exert enhanced negative feedback effects on pituitary function. The tumors provide a good model for endocrinologically active hormone-dependent tumors.

Prepubertal changes in immunoreactive inhibin concentration in blood serum and testicular tissue in Holstein bull calves.

Age-related changes in immunoreactive inhibin (ir-inhibin) levels and the relationship among ir-inhibin, gonadotropins and testosterone were examined in 53 Holstein bull calves from neonates to 8.6 months old. Serum levels of ir-inhibin, luteinizing hormone (LH), follicle stimulating hormone (FSH) and testosterone, as well as ir-inhibin levels in testicular extracts, and testicular sizes were measured. All hormones were measured by specific radioimmunoassays. The concentrations of ir-inhibin in serum and testicular tissue were high in neonatal calves and tended to decrease with age. In contrast, serum concentrations of gonadotropins did not show any age-related changes within the experimental period. Serum testosterone levels and testicular sizes (length, width and weight) were positively correlated with age. Furthermore, a positive immunostaining to antiserum for the inhibin alpha-subunit was immunocytochemically observed only in Sertoli cells of the seminiferous tubules from neonates to calves less than 6 months old. These results indicate that the immature bovine testis produces and secretes high levels of ir-inhibin and that the Sertoli cells are a major source of ir-inhibin in prepubertal bull calves.

Inhibins A and B are regulated differentially in the early post-partum period.

The early postpartum period is characterized endocrinologically by a rapid fall in the levels of oestradiol (E2) and immunoreactive inhibin, and a delayed rise in serum follicle stimulating hormone (FSH). No description is currently available of changes in serum inhibins A and B. The present study aimed to examine the levels of inhibin A and B during the early weeks of postpartum lactational amenorrhoea, to determine whether there was evidence for differential regulation of the two hormones at a time when no dominant follicle was developing in the ovary. Serum samples were available from 12 subjects aged 29-38 in whom postpartum levels of FSH, immunoreactive inhibin, E2 and prolactin had been examined previously. Samples for hormone assays had been obtained prior to delivery, daily for the 3-5 days postpartum, and weekly thereafter. Inhibins A and B were measured by specific ELISA assays, and results were calculated as 10 day averages for samples obtained on days 1-10, 11-20, 21-30, etc. postpartum. Normal hormone concentrations for reference were obtained from volunteers, also aged 29-38, sampled on days 3-5 of a normal menstrual cycle. Inhibin A in the predelivery sample ranged from 62 to 1243 ng/l, geometric mean 592. Concentrations fell rapidly postpartum and reached a nadir in the low follicular phase range between days 5 and 37 postdelivery, mean 13.6 days. The concentrations of both inhibin B and FSH rose 14-27 days postpartum from their initially low postdelivery levels, to reach the normal follicular phase range. These increases in concentration were significantly correlated in all individual subjects. The secretion of inhibin A and B is regulated differentially during the early stages of lactational amenorrhoea, just as it is in the late luteal phase of the normal menstrual cycle. Whilst inhibin A falls postpartum, reflecting cessation of placental function, and remains low until ovulatory cycles are resumed, FSH and inhibin B rise after a delay of two weeks or more. It is postulated that the rise of inhibin B is the result of secretion from a cohort of small follicles stimulated by rising FSH levels.

Inhibin Subunit Gene Expression in Ovarian Cancer

Objective(s).Granulosa cell tumors (GCT) and mucinous cystadenocarcinoma of the ovary are associated with elevated circulating levels of immunoreactive inhibin. Measurement of serum inhibin levels provides a useful tumor marker in the management of ovarian tumors. Inhibin is a dimeric ovarian glycoprotein hormone consisting of one α and one of two β subunits. The β subunits can dimerize to form activin. Activin is bound and its action modulated by another gonadal peptide, follistatin. In this study the patterns of expression of the three inhibin subunit genes, the follistatin gene, and the activin receptor type II gene have been determined.Methods.Gene expression was analyzed in RNA prepared from 16 primary ovarian tumors using reverse transcriptase-polymerase chain reaction (RT-PCR). Gene-specific primes were used for RT-PCR; the products were analyzed by Southern blot analysis with gene-specific32P-labeled probes.Results.Widespread expression of these genes was found in all of the tumor types examined. Abundant expression of the inhibin α subunit gene was observed in the GCT and to a lesser extent in the mucinous and serous tumors. β subunit expression was also present in the GCT and to a lesser extent in the other tumors. Widespread expression of both the activin receptor type II and the follistatin genes was also observed.Conclusions.Expression of the inhibin subunit genes in GCT and some epithelial tumors confirms that these tumors are the source of the increased immunoreactive inhibin seen in the circulation of patients with ovarian tumors. Expression of the activin receptor type II and follistatin genes suggests a paracrine role for activin in these tumors which may be modulated by follistatin, particularly in the GCT.

Inhibin and ovarian cancer

Previous observations from our laboratory have demonstrated that the levels of immunoreactive inhibin (ir-inh) are elevated in almost all patients with granulosa cell tumours and in the majority of postmenopausal women with mucinous ovarian cancers. The present manuscript confirms these findings in a larger group of postmenopausal women. Immunohistochemistry for the inhibin α, β A and β B subunits shows predominantly epithelial staining in granulosa cell tumours and in the majority of mucinous cancers. Serous cystadenocarcinomas also frequently show positive staining. Studies seeking to identify G α i-2 or FSH receptor mutations have provided negative results in contrast to other reports. Further studies of the roles of the inhibin-related family of peptides in ovarian cancer diagnosis and monitoring are clearly indicated.

Effects of growth hormone, activin, and follistatin on the development of preantral follicle from immature female mice.

The aim of this study was to investigate whether GH and insulin-like growth factor I (IGF-I) are involved in preantral folliculogenesis and, if so, to clarify the relationship between GH/IGF-I and activin/follistatin (FS) systems in immature female mice. Ovaries were obtained from 11-day-old mice, and preantral follicles, 100-105 microm in diameter, were mechanically isolated and selected for culture. Ten preantral follicles per well were cultured with different quantities and combinations of additives as follows: no additives (control), recombinant human FSH (rhFSH), IGF-I, recombinant human GH (rhGH), activin A, and recombinant human FS (rhFS). Mean diameters of the follicles were measured daily, and estradiol and immunoreactive inhibin levels in the cultured medium were assayed by RIA on day 4. rhGH showed stimulatory effects on the follicular diameter and the secretion of estradiol and immunoreactive inhibin. These effects were augmented by the presence of IGF-I and activin A. IGF-I alone did not show any stimulatory effect. The addition of rhFSH to activin A or to rhGH and activin A promoted preantral follicular growth and hormone production. On the other hand, GH- or activin-stimulated follicular growth was suppressed by rhFS in a dose-dependent manner. These results indicate that activin A and rhGH may play an important role in controlling earlier phases of follicular development during the infantile period, which is considered to be gonadotropin independent.

Effects of chemotherapy-induced testicular damage on inhibin, gonadotropin, and testosterone secretion: a prospective longitudinal study.

To investigate the role of inhibin in the control of follicle-stimulating hormone (FSH) secretion, we have measured levels of immunoreactive inhibin (ir-inhibin), inhibin B, Pro-alpha C containing inhibins, FSH, luteinizing hormone (LH), and testosterone in twelve men with hematological malignancies before, during, and after chemotherapy. Inhibin B levels fell significantly by 1 month from a mean +/- SE baseline level of 273.2 +/- 32.8 pg/mL, reaching a nadir of 52.6 +/- 15.3 pg/mL at 4 months (P < 0.0001). FSH levels increased within the first month from a baseline level of 3.9 +/- 0.6 IU/L, reaching a peak level of 22.4 +/- 3.3 IU/L at 4 months (P < 0.0001). FSH and inhibin B were significantly and inversely correlated (r = 0.69, P < 0.0001). Pro-alpha C containing inhibin levels increased significantly (P < 0.05) at 3 months and were significantly and positively correlated with FSH (r = 0.38, P = 0.002). LH levels increased significantly but to a much lesser extent than FSH, the increase becoming evident only 4 months after treatment commenced (P < 0.03). Levels of ir-inhibin and testosterone remained unchanged throughout the study. These data provide strong support to the hypothesis that inhibin B is the physiologically important form of inhibin in men, negatively regulating FSH secretion at the pituitary. Furthermore, they suggest that FSH stimulates inhibin alpha-subunit secretion by the testis.

Gonadectomy permits adrenocortical tumorigenesis in mice transgenic for the mouse inhibin alpha-subunit promoter/simian virus 40 T-antigen fusion gene: evidence for negative autoregulation of the inhibin alpha-subunit gene.

We have developed a transgenic (TG) mouse model for gonadal tumorigenesis expressing the Simian virus 40 T-antigen (Tag) under the mouse inhibin alpha-subunit promoter. Gonadal tumors appear with 100% penetrance by the age of 5-8 months in the TG mice. When 1-month-old TG mice were gonadectomized, adrenal gland tumors were observed in each animal (12 females, 11 males) at the age of 6-8 months. No adrenal tumors were detected in gonadectomized non-TG mice (nine females, nine males) or in the intact TG mice (n > 100). The tumors appeared to originate from the X zone of the adrenal cortex. The TG mice with adrenocortical tumors had elevated serum levels of progesterone, estradiol, and immunoreactive inhibin (including dimeric forms), but corticosterone secretion was reduced. The lack of adrenal tumors in intact TG mice suggested that the tumorous gonads secrete factor(s) inhibiting adrenal tumorigenesis. As a candidate molecule, we studied the effects of inhibin, which was high in the serum of control females and TG females with ovarian tumors, as well as in TG males with testicular tumors. The DNA synthesis, as well as the levels of inhibin-alpha and Tag mRNA expression, were significantly reduced by recombinant human inhibin A in cell cultures derived from the adrenal tumors. In accordance, the expression level of inhibin-alpha mRNA in the normal adrenal gland was elevated 2 weeks after gonadectomy. These findings suggest that gonadal inhibin can down-regulate the expression of the inhibin alpha-subunit gene in the adrenal gland. When circulating inhibin is eliminated by gonadectomy, Tag expression and tumorigenesis are stimulated in the adrenal glands of the TG mice. The results demonstrate a novel mechanism of autoregulation in inhibin alpha-subunit gene expression.

Recombinant human inhibin-A administered early in the menstrual cycle alters concurrent pituitary and follicular, plus subsequent luteal, function in rhesus monkeys.

Inhibin, a suppressor of pituitary FSH secretion in nonprimate species, may also act in the ovary to regulate follicular development. To examine whether inhibin has similar actions in primates, female rhesus monkeys (n = 3/treatment), exhibiting regular menstrual cycles, received sc injections of either vehicle or 60 micrograms/kg recombinant human inhibin-A at 0800 and 1600 h for 5 days beginning at menses. The vehicle-treated monkeys displayed menstrual cycles of normal length, with the follicular (11.3 +/- 2.5 days, mean +/- SE) and luteal (16.3 +/- 2.5 days) phases demarcated by midcycle peaks in serum estradiol (E) and bioactive LH. After the first inhibin injection, levels of immunoreactive inhibin A peaked at 10 ng/mL within 1 h and returned to baseline (< 0.1 ng/mL) before the second injection 8 h later. Although serum E and LH did not change, bioactive FSH decreased (to 66% of pretreatment levels, P < 0.05) within 8 h. Within 1 day, circulating bioactive FSH was less (P < 0.05) in inhibin-treated monkeys, compared with controls. By 2-3 days, serum E levels were also markedly (P < 0.05) reduced in inhibin-treated animals, whereas bioactive LH rose 3-fold (P < 0.05). After inhibin treatment, the midcycle rises in serum E and LH were delayed; hence, the follicular phase was prolonged (15.0 +/- 2.6 days, P < 0.05), compared with controls. Although the patterns and levels of serum LH circulating during the subsequent luteal phase seemed comparable in both groups, mean progesterone levels were suppressed to 2-3 ng/mL (P < 0.05) during the midluteal phase in inhibin-treated monkeys. However, the length of the luteal phase in inhibin-treated cycles (13.0 +/- 2.6 days) was not significantly altered. We conclude that exogenous inhibin rapidly diminishes pituitary FSH secretion in female monkeys during the early follicular phase of the menstrual cycle. This action, and/or other actions directly on the ovary, leads to subsequent effects on follicular steroidogenesis and pituitary LH secretion that culminate in an aberrant ovarian cycle characterized by an insufficient luteal phase. The study identifies, for the first time, possible activities and roles of inhibin during the ovarian cycle in primates.