Effects of passive immunization of ewes against an inhibin-peptide on gonadotropin levels, ovulation rate, and prolificacy

The experimental objectives were to determine whether injection of semi-purified (sp; ammonium sulfate-precipitated) and highly purified (hp; immunoaffinity-purified) ovine antibody (Ab) against an inhibin-peptide fragment (alpha-IF) before the preovulatory period would 1) stimulate FSH secretion in a dose-response manner, 2) induce an increase in ovulation rate, and 3) affect pregnancy rate and prolificacy (lambs born alive per ewe lambing). During the early breeding season, estrus was synchronized in 30 2-yr-old crossbred ewes through use of progesterone-releasing pessaries (CIDR-G). Two doses (330 and 660 laboratory reference preparation [RP-2] kU) of sp- and hp-alpha-IF-Ab were injected i.m. 48 h before CIDR-G removal (6 ewes per group). Six other ewes received control solution. Plasma alpha-IF-Ab titers peaked at 12 h postinjection. Plasma FSH levels were higher (p < 0.02) in alpha-IF-Ab-treated ewes than in control ewes from 12 to 24 h postimmunization. Magnitudes of FSH increases were similar in ewes administered sp- and hp-alpha-IF-Ab and were greater (p < 0.05) in ewes receiving 660 than in those receiving 330 RP-2 kU. Compared to control values, the higher alpha-IF-Ab dose increased FSH levels by 44 +/- 5% and the lower dose increased the levels by 22 +/- 3%. Plasma LH levels were similar among passively immunized and control sheep. Ovulation rate was increased (p < 0.0005) by alpha-IF-Ab treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibin and activin are demonstrable by immunohistochemistry in ovarian tumor tissue

Elevated serum immunoreactive inhibin concentrations have been reported in patients with mucinous and granulosa cell tumors of the ovary. The present study aimed to determine whether the inhibins and/or the related peptides, the activins, were demonstrable within ovarian tumor tissue. Immunohistochemical analyses were performed on 11 ovarian tumors, 5 mucinous, 3 serous, 1 granulosa, 1 clear cell, and 1 metastatic colonic cancer. Both monoclonal and polyclonal antisera specific for inhibin-A, activin-A, and activin-B, and their alpha-, beta A- and beta B-subunits were used. The mucinous cells of all five mucinous tumors showed positive staining for activin-A and activin-B, and their beta A- and beta B-subunits, and three stained positive for inhibin-A and the alpha-subunit. The granulosa cell tumor also showed positive staining for inhibin-A and the activins. The remaining tumors were negative. The findings are consistent with the hypersecretion of inhibin (and possibly activin) by some ovarian malignancies and suggest that immunohistochemistry for the inhibins and the activins should be explored further in the classification of ovarian malignancies.

Inhibin functions in male rats

The role of inhibin in modulating FSH secretion at sexual maturation in male rats was studied using antibodies against inhibin alpha subunit. An immunohistochemical study was performed by immunogold-silver staining; modulation of FSH secretion in sexual maturation was studied by immunoneutralization. The results show that immunoreactive inhibin alpha subunit is localized in the Sertoli cell, especially at young ages. There were no significant differences in testes weights and histology between the antibody-administered group and the control group. Marked FSH increase was observed in the antibody-administered group from 5 to 30 days. No significant difference was detected in the over 50 days group. It would appear that inhibin plays a role in suppressing FSH secretion in infantile male rats, especially before puberty. However, inhibin's role might not be particularly important, as shown by the lack of significant changes in the gonads of antibody-administered group.

Identification of biologically active inhibin in the peritoneal fluid of women

PURPOSE

Immunoreactive inhibin (i-inhibin) has been reported to be present in the peritoneal fluid of women. The radioimmunoassay employed measures free, biologically inactive alpha-subunits(s) equally as well as dimeric, biologically active inhibin. The present study was designed to determine if biologically active, dimeric inhibin is present in the peritoneal fluid of women.

METHODS

Peritoneal fluid of four women was assayed by radioimmunoassay, a sheep pituitary bioassay, and two ELISA procedures which utilized specific monoclonal antibodies for the "capture" of the alpha-subunit (ELISA-A) or the beta-subunit (ELISA-B) of inhibin and subsequent quantification of dimeric inhibin-A.

RESULTS

There was a good correlation between the values obtained by radioimmunoassay, bioassay, and both ELISAs; two samples (from the late follicular phase) with relatively high i-inhibin concentrations were positive in all four assays, whereas two samples (from the early follicular phase) with very low i-inhibin concentrations were negative in the bioassay and ELISAs.

CONCLUSION

A significant portion of the immunoreactive inhibin in the peritoneal fluid obtained during the late follicular phase of women is dimeric, biologically active inhibin. We speculate that this may have potential implications for oocyte maturation and early embryogenesis within the oviduct.

Antibodies to human seminal plasma inhibin adversely affect sperm function parameters

Polyclonal antibodies to intact inhibin (94 amino acids, R-94, 10.5 kDa) and its sequence specific synthetic fragments (R-9, R-17) were evaluated for their effect on various physical and biochemical parameters of sperm function. Intact inhibit had maximum deleterious effect on quantitative motility and mean forward progression of spermatozoa. Antibodies had no effect on sperm fructolysis and sperm nuclear chromatin decondensation reaction. Sperm plasma membrane was damaged in antibodies treated spermatozoa as evidenced by hypoosmotic swelling test and sperm lipid peroxidation reaction.

Manipulation of inhibin during the luteal-follicular phase transition of the primate menstrual cycle fails to affect FSH secretion

The pattern of inhibin concentrations in blood during the menstrual cycle in primates has suggested an endocrine role of inhibin in the negative feedback control of FSH secretion during the luteal phase. Conversely, the fall in inhibin during the late luteal phase may play a role in the rise in serum FSH during the luteal-follicular phase transition. This hypothesis was examined by determining the effects of manipulation of inhibin on FSH secretion in stumptailed macaques. During the mid-luteal phase the putative inhibin feedback was inhibited by i.v. administration of 20 ml of ovine antiserum to human recombinant inhibin in 4 macaques. FSH secretion was unaffected during the initial 24 h period post-treatment and the timing of the rise in FSH which occurred during the subsequent luteal-follicular phase transition was normal. To determine whether the elevated serum concentrations of FSH observed during the early follicular phase could be reduced by administration of inhibin, 5 cyclic macaques were treated with 200 micrograms of recombinant human inhibin i.v. Serum FSH concentrations were unaltered. These results suggest that inhibin does not play a major role in modulating FSH secretion during the luteal-follicular phase transition.

Active immunization of heifers against inhibin: effects on plasma concentrations of gonadotrophins, steroids and ovarian follicular dynamics during prostaglandin-synchronized cycles

We reported previously that active immunization of heifers using a synthetic peptide-based inhibin vaccine (bI alpha(1-29)Tyr30) can enhance ovarian follicular development and ovulation rate during spontaneous oestrous cycles. To extend this study, we investigated the effect of inhibin immunization more closely by monitoring plasma hormone profiles and ovarian activity in bI alpha(1-29)Tyr30-immunized and control (ovalbumin-immunized) heifers (n = 6 per group) over three consecutive oestrous cycles, which were synchronized and shortened by administering a PGF2 alpha analogue at intervals of 14 days. Blood samples were collected at 2-8 h intervals for 40 days and the ovaries were examined daily using ultrasonography. Repeated-measures ANOVA showed that inhibin immunization significantly increased plasma FSH concentration (by 52% overall; P < 0.01) and ovulation rate (by 58%; P < 0.01). Both immunized and control heifers showed the same cyclic pattern of plasma FSH (treatment x time interaction; not significant), indicating that the increase in plasma FSH was sustained throughout the cycle. Immunization did not affect the concentration or pattern of secretion of LH, oestradiol or progesterone and had no influence on the timing of the LH surge or ovulation after PG injection. While inhibin immunization increased the number of 'large' (i.e. growing to > or = 10 mm diameter) follicles that developed during both the preovulatory (by 90%, P < 0.02) and postovulatory (by 190%, P < 0.01) period, there was no difference between groups in the temporal pattern of growth or regression of large follicles or of corpora lutea.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of inhibin immunoneutralization on steroidogenesis in rat ovarian follicles in vitro

Inhibin is a putative gonadal paracrine factor produced by FSH-stimulated granulosa cells. To assess the paracrine function of inhibin further, preantral follicles (approx. 240 microns) with attached thecal cells were isolated mechanically from immature rat ovaries and cultured individually in vitro for 5 days in medium containing homologous serum and FSH. After 5 days, follicles had grown to preovulatory size (approx. 470 microns) with a commensurate increase in oestradiol secretion but not progesterone. Immunoneutralization of endogenous inhibin resulted in a significant decrease in oestradiol secretion and an increase in progesterone accumulation. When antiserum-treated follicles were supplemented with exogenous inhibin, oestradiol secretion was restored and progesterone accumulation was reduced. Aromatase substrate (androstenedione) levels were too low to measure, regardless of antiserum treatment. However, follicles treated with inhibin antiserum in the presence of exogenous androstenedione also exhibited oestradiol levels similar to untreated controls while progesterone accumulation remained elevated. We interpret these data as evidence that inhibin secreted by FSH-stimulated granulosa cells exerts a physiologically significant paracrine function in the follicle wall. Based on previous observations that inhibin stimulates androgen synthesis by isolated thecal/interstitial cells, it is proposed that granulosa-derived inhibin promotes thecal androgen synthesis and hence oestrogen synthesis during preovulatory follicle development. The antiserum-induced increase in progesterone accumulation is most probably explained by reduced metabolism of C21 steroid substrate to androgen in thecal/interstitial cells deprived of inhibin. It is concluded that inhibin is a physiological modulator of follicular steroidogenesis which exerts its effect at the level of thecal cell androgen synthesis.

Human follicular fluid contains pro- and C-terminal immunoreactive alpha-inhibin precursor proteins

The majority of immunoactive inhibin in human follicular fluid (hFF) is devoid of pituitary cell bioactivity and is hypothesized to contain alpha-inhibin monomeric proteins known to cross-react with an inhibin antiserum (Monash 1989). The aim of this study was to define more precisely the nature of these inhibin-immunoreactive proteins using alpha-inhibin sequence-specific antisera. First, a polyclonal antiserum was raised to precursor amino acids 21-35 (PIN-1) and was used in a RIA to measure pro-alpha-inhibin-immunoreactive proteins. Western blotting was used to confirm these findings. Secondly, the binding epitope of the Monash antiserum was defined by peptide analysis to be located within the C-terminus (precursor amino acids 326-341) of alpha-inhibin, and this assay was then used to monitor the presence of C-terminal sequences. Similar levels of pro-alpha-inhibin immunoreactivity (PIN-1 RIA; N-terminus alpha-inhibin precursor) were detected in hFF collected from women with normal menstrual cycles during the follicular phase and from multiple follicles from a woman undergoing ovarian hyperstimulation during an in vitro fertilization (IVF) protocol. Western blotting with the PIN-1 antibody confirmed the presence of immunoreactive proteins of 57,000 and 29,000 mol wt in the follicular fluids of both normal cycle and IVF follicles. However, ovarian hyperstimulation elevated intrafollicular C-terminal immunoreactivity (Monash RIA) compared to that in normal cycle hFF. Furthermore, intrafollicular estradiol and progesterone were significantly correlated to C-terminal activity in follicles from IVF, but not in normal cycles. These data show that 1) both pro- and C-terminal alpha-inhibin proteins are secreted into follicular fluids from normal and IVF cycles, suggesting that alpha-inhibin precursor proteins may be physiologically relevant in the process of folliculogenesis; and 2) IVF and normal cycle follicular fluids differ in their production and processing of inhibin.

Effects of alpha-inhibin-92 fragments and alpha-inhibin-92 antiserum on the control of follicle-stimulating hormone release in male rats

Alpha-inhibin-92 (alpha-IB-92) has been characterized from human seminal plasma and found to be active in suppressing FSH release in vitro and in vivo. In order to determine if smaller fragments of this 92 amino acid peptide would still be active to suppress FSH release, we have evaluated 5 of these fragments for their effects on FSH and LH release in the present study. Five alpha-IB-92 fragments (1-34, 1-46, 35-65, 35-92 and 66-92) were synthesized and injected intravenously (iv) into castrated adult rats (2 days post operation). Only fragments alpha-IB-92-(35-65) and alpha-IB-92-(66-92) significantly lowered plasma FSH, but not LH, at doses of 10 micrograms. These fragments exerted a preferential FSH-suppressing effect, but their activities were less than that of alpha-IB-92. In view of the rapid action of these peptides and the preferential FSH suppressing effect, they could be useful clinically to suppress FSH release. To determine the possible physiologic significance of alpha-IB-92, we injected antiserum raised against alpha-IB-92 into immature male rats and evaluated its effects on FSH and LH release. Normal rabbit serum (NRS) or anti-alpha-IB-92 serum was injected iv through indwelling jugular catheters into conscious, unrestrained 18 day-old male rats. Blood samples (0.2 ml) were collected at various intervals. Intravenous injection of alpha-IB-92 antiserum (0.1 ml/rat) selectively elevated plasma levels of FSH but not LH from 2-8 h post-injection in 18 day-old male rats (P < 0.01). Since immunoneutralization of alpha-IB-92 significantly elevated FSH release in immature rats, alpha-IB-92 has a physiological inhibiting role in control of FSH but not LH release at this stage of development.

Pituitary and ovarian function in ewes immunized against the amino-terminal peptide (alpha N) of the inhibin alpha 43-subunit

Immunization of ewes against the amino-terminal peptide (alpha N) of the pro-alpha-subunit of inhibin has been shown to reduce fertility, thought to be due to disruption of ovulation. The aims of this study were to examine the effects of active immunization of ewes against alpha N on circulating concentrations of FSH, LH and on ovarian inhibin and progesterone, and to relate these observations to number of corpora lutea and oocyte recovery rates. Ewes were immunized against one or both of two recombinant full length bovine-alpha N immunogens (FP1 and FP2). Three experiments were performed in which jugular venous plasma was sampled from control and immunized ewes: (1) hourly across the oestrous surge of gonadotrophins (Expt 1); (2) daily for one entire oestrous cycle, and in the subsequent cycle, oviducts were flushed to recover ovulated eggs (Expt 2); and (3) samples were taken at 10 min intervals during the follicular and luteal phases (Expt 3). Binding of 125I-labelled alpha N1-26 to serum was greater (P < 0.05) in immunized groups than in controls for all experiments. The number of eggs per corpus luteum recovered from the oviducts was lower (P < 0.05) in the alpha N-immunized groups (39%) than in controls (88%). There were more (P < 0.05) corpora lutea per ewe in FP2 immunized groups 4 (1.8 +/- 0.45) and 5 (1.75 +/- 0.5) than in the control group (1.13 +/- 0.13), but no increase in group 3 (FP1; 1.4 +/- 0.24).(ABSTRACT TRUNCATED AT 250 WORDS)

Immunoassays for inhibin and its subunits. Further applications of the synthetic peptide approach

We describe the preparation of a new rat monoclonal antibody (CRC1) to the N-terminal sequence of the 43 kDa subunit of human ovarian inhibin, and its use together with other anti-peptide monoclonal antibodies, in two-site immunoassays for the detection of inhibin-related material in biological fluids. The Fab fraction of a mouse monoclonal antibody (R1) to the N-terminal portion of the 20 kDa alpha subunit, coupled to alkaline phosphatase, was used for detection, and either CRC1 or a monoclonal antibody (E4) to the beta-A subunit were used as capture antibodies. The E4/R1 combination, expected to measure dimeric bioactive inhibin, could detect less than 2 pg/ml of recombinant inhibin in diluent, gave good recovery of activity spiked into human blood, and could measure significant levels of immunoreactivity in sera from women undergoing ovulation induction, and in some normal women. Sera from post-menopausal women contained undetectable levels. Apparent inhibin levels in human follicular fluid were increased six-fold by pretreatment with 8 M urea, suggesting masking of epitopes in this fluid. Activin cross-reactivity in the assay was 0.05%. The R1/CRC1 assay, expected to measure only large molecular weight forms of inhibin or its alpha subunit, could detect immunoreactivity in human FF diluted 50,000-fold, and in all sera tested, although the levels in the hyperovulated women were higher. By contrast to the E4/R1 assay much of the immunoreactivity was labile during the clotting process, or subsequent assay, and reliable measurements on blood with this assay will require special sample collection procedures. These results demonstrate the value of anti-peptide monoclonal antibodies in the study of inhibin, and the results obtained with CRC1 show that antibodies useful for immunoassays can sometimes be obtained without the purified target molecule being available for immunization or screening.

RU486 blocks the effects of inhibin antiserum or luteinizing hormone on the secondary follicle-stimulating hormone surge

Previous work in this laboratory has shown that when the antiprogesterone RU486 is administered at 1230 h on proestrus, the primary surges of LH and FSH are significantly attenuated, and the secondary FSH surge is abolished. This suppression of the secondary FSH surge occurs in RU486-treated rats despite a drop in serum inhibin, which is presumably due to the partial primary LH surge. The experiments described investigated the interrelationships among the primary LH surge, the rising proestrous levels of progesterone, and the falling levels of inhibin on proestrus on the selective secretion of FSH during the night of proestrus and the morning of estrus. Exogenous LH given to rats treated first with RU486 cannot restore the secondary surge of FSH, as it does in GnRH antagonist-blocked rats, and progesterone alone cannot restore the secondary FSH surge in an animal in which the surges are blocked with GnRH antagonist. Antiserum to inhibin superimposed on GnRH antagonist causes an enhancement of FSH levels beyond that of the secondary FSH surge, but antiserum to inhibin superimposed on RU486 does not induce a similar elevation of FSH secretion. The failure of antiserum to inhibin to increase FSH in the face of RU486 suggests that either a small amount of progesterone, or perhaps another hormone blocked by RU486, is needed to facilitate FSH secretion in response to the drop in inhibin or RU486 is acting through nonprogesterone-mediated effects to block pituitary FSH secretion.

Development of a specific and sensitive two-site enzyme-linked immunosorbent assay for measurement of inhibin-A in serum

A polyclonal chicken antiserum against purified 32-kilodalton (kDa) recombinant inhibin-A (rh-InhA) and two monoclonal antibodies (mAb) against either rh-InhA (11B5) or 28-kDa recombinant activin-A (rh-ActA; 9A9) were used to develop three sensitive InhA enzyme-linked immunosorbent assays (ELISAs). The sensitivity of an ELISA using affinity-purified chicken anti-rh-InhA (Ck) for both coat and capture (Ck/Ck) averaged 78 +/- 3 pg/ml, while the mAb/Ck ELISAs (11B5/Ck or 9A9/Ck) averaged 100 +/- 6 pg/ml in a 10% serum matrix, with intra-and interassay coefficients of variation of 2-5% and 8-10%, respectively, for all assays. The ELISA formats did not cross-react with purified rh-ActA or recombinant human transforming growth factor-beta 1 or detect any immunoreactive proteins in medium conditioned by cell lines expressing rh-ActA or recombinant human transforming growth factor-beta 1. The Ck/Ck ELISA detected significant amounts of immunoreactivity in medium from cells expressing the free alpha-subunit of inhibin and recombinant inhibin-B (rh-InhB). In contrast, the mAb/Ck ELISAs showed no cross-reactivity to medium conditioned by these two cell lines. All three ELISA formats detected rh-InhA added to either human or rat serum in vitro or serum from rats injected with rhInhA. The Ck/Ck and 9A9/Ck ELISAs successfully quantitated inhibin in sera from patients undergoing ovulation induction and in rats (with or without sc administration of pregnant female serum gonadotropin). The 11B5/Ck ELISA appeared to be specific for the 32-kDa form of inhibin, while the 9A9/Ck ELISA was useful in quantitating inhibin-A in biological fluids, with little cross-reactivity to free alpha-chain or inhibin-B.

Antifertility effects in female rats immunized with human seminal plasma inhibin

Adult female rats were actively immunized with sperm-coating protein (10.4 KDa) human seminal plasma inhibin (HSPI). Following 8 weeks of immunization at 2.5 micrograms and 5 micrograms doses of HSPI with Freund's complete adjuvant, antifertility effects were observed in 63% (5/8) and 88% (7/8) of animals, respectively. Estrous cycle was not affected in experimental group. Thus, the present study suggests the potential use of HSPI for immunocontraception in females.

Involvement of inhibin in the regulation of FSH secretion in prepubertal bulls

To investigate the physiological importance of inhibin in the regulation of FSH secretion in prepubertal bulls, animals (6-month-old) were passively immunized against inhibin. Five animals were given an i.v. bolus injection of 50 ml inhibin antiserum raised against bovine 32 kDa inhibin in a castrated male goat, and four bulls were given the same amount of castrated male goat serum (control serum) as controls. Treatment with the inhibin antiserum resulted in a marked increase (P < 0.01) in plasma concentrations of FSH within 12 h compared with control animals, and FSH levels in immunized animals remained high until 168 h after the injection. Concentrations of plasma LH and testosterone in the immunized animals were not different from those in the control animals. The present findings provide strong evidence that inhibin plays an important role in the inhibitory regulation of FSH secretion in prepubertal bulls.

Ovulatory and endocrine responses after active immunization of gilts against a synthetic fragment of bovine inhibin

The objective of this study was to determine whether neutralizing endogenous inhibin would affect ovulation rate and serum concentrations of FSH, LH, estradiol-17 beta, and progesterone in gilts. At wk 0, during their second postpubertal estrous cycle, gilts (195 +/- 2.4 d of age) were given a primary immunization against the 1-26 gly-tyr NH-terminal amino acid sequence of bovine inhibin-alpha conjugated to human alpha globulin (INH; n = 10) or against human alpha globulin alone (control; n = 10). The primary immunization mixed with Freund's complete adjuvant contained .915 mg of the inhibin peptide. Booster immunizations in Freund's incomplete adjuvant contained .3 and .183 mg of the inhibin peptide and were given at wk 8 and 12, respectively. Free, unconjugated inhibin was given to INH gilts at 16 wk. Blood samples for determination of hormones were collected every 4 h beginning on d 15 of the first estrous cycle beyond wk 16 (first cycle) and continuing until d 5 of the second estrous cycle following wk 16 (second cycle). Ovulation rate was estimated by laparoscopy during the second cycle. Antibody titers were estimated by determining the percentage of [125I]-INH bound by serum diluted 1:4,000. The antibody titers were 17 +/- 2, 22 +/- 3, and 9 +/- 1% at wk 9, 17, and 23 for INH gilts, respectively, and 0% at all times for control gilts. Duration of three consecutive estrous cycles terminating with the first experimental cycle did not differ between treatments (INH, 20.7 +/- .3 vs control, 20.4 +/- .3 d).(ABSTRACT TRUNCATED AT 250 WORDS)

Immunocytochemical evidence for the presence of inhibin and activin-like proteins and their localization in goldfish gonads

In previous studies, we have demonstrated that inhibin and activin are stimulatory to goldfish gonadotropin release. In the present study, the distribution of immunoreactive inhibin and activin subunits (alpha, beta A, and beta B) in goldfish gonads was examined with domain-specific antibodies against mammalian inhibin and activin subunits, using the avidin-biotin-peroxidase complex method. In the ovary, follicle cells surrounding the oocyte were heavily stained with anti-porcine beta A and human beta B subunits. The cytoplasm of previtellogenic oocytes, at all stages of the ovarian cycle, also showed strong reactions with anti-beta A and beta B. As ovarian recrudescence progressed, oocytes that started to accumulate cortical vesicles gradually lost their immunoreactivity, with the reaction intensity inversely proportional to the amount of cortical vesicles in the oocyte; when oocytes became full of cortical vesicles, the oocytoplasm was no longer immunoreactive to anti-beta A and beta B. The staining with antiporcine alpha subunit was similar to that with anti-beta A and beta B but the reaction intensity was weaker than that with anti-beta A and beta B. In the testis, the mature sperm in the tubular lumen exhibited a strong immunoreaction to anti-alpha antibody, while the interstitial tissue was completely negative. However, the immunoreactivities with anti-beta A and beta B in the testis were exclusively restricted to the interstitial tissues. These results provide evidence for the presence of inhibin and activin-like molecules in the goldfish and reveal the distribution of these molecules in the goldfish gonads.

Ovariectomy and inhibin immunoneutralization acutely increase follicle-stimulating hormone-beta messenger ribonucleic acid concentrations: evidence for a nontranscriptional mechanism

After ovariectomy (ovx), FSH beta mRNA levels and serum FSH increase 2- to 3-fold within 12 h, and this persists in the presence of a GnRH antagonist. As a fall in plasma estradiol and progesterone appears to regulate FSH beta via increased GnRH secretion, it is thought that the acute (by 2 h) changes in FSH beta mRNA after ovx reflect falling levels of plasma inhibin. The current study addressed the following questions. 1) Does a reduction of circulating inhibin (via passive immunoneutralization or gonadectomy) increase FSH beta mRNA levels? 2) If so, are the acute increases in FSH beta mRNA associated with changes in the transcription rate? Adult male and female rats received 0.5 ml antiinhibin antiserum, iv, and were killed 2 or 12 h later. A second group of rats was gonadectomized; some received a GnRH antagonist and were killed at various intervals between 2 h and 7 days later. In adult males, no change in gonadotropin mRNA levels was observed after either addition of inhibin antiserum or removal of the testes. In contrast, in adult female rats, both ovx and inhibin antiserum increased FSH beta mRNA levels (2-fold) within 2 h, and a similar increase occurred in the presence of a GnRH antagonist. To determine if the increase in FSH beta resulted from increased mRNA synthesis, adult female rats were ovx, and half received a GnRH antagonist. Animals were killed 2 or 12 h later, and transcription rates were measured by nuclear run-off assay in pituitaries pooled from three rats. The transcription rate of the alpha-subunit, although not altered by ovx, was decreased in animals receiving the GnRH antagonist. Transcription of the LH beta gene was increased within 2 h after ovx, a change that was abolished by the GnRH antagonist. mRNA concentrations of either alpha or LH beta do not increase acutely after ovx, suggesting that GnRH regulates alpha and LH beta gene transcription and 12 h or more of mRNA synthesis are required to increase cytoplasmic concentrations. The FSH beta gene transcription rate was unchanged in both ovx and GnRH antagonist-treated animals, but serum FSH increased at 12 h. These data indicate that the rapid GnRH-independent increase in FSH beta mRNA levels seen immediately after ovx is not associated with altered mRNA synthesis and suggest that inhibin may also regulate FSH beta gene expression through nontranscriptional mechanisms.

Follicular development and ovarian hormone secretion following passive immunization of ewes against inhibin or oestradiol

Immunization against inhibin or oestradiol causes an increase in the peripheral plasma concentration of FSH. In this study we have investigated the effect of this post-immunization rise in FSH concentration on follicular development by means of real-time ultrasonography, in ewes in which an ovary and its vascular pedicle had been autotransplanted to a site in the neck. Groups of ewes on day 10 of the luteal phase of the oestrous cycle were injected with a single 10 ml i.v. bolus of plasma from normal ewes (control; n = 4), antiserum to the 1-26 peptide fragment of the N-terminus of the alpha chain of porcine inhibin (n = 5) or antiserum to oestradiol-17 beta (n = 4). The plasma concentration of FSH was unaffected by treatment in the control group but showed a significant (P < 0.001) rise following treatment in both immunized groups (inhibin-immunized 175% over 19h; oestradiol-immunized 138% over 22 h as a per cent of the original value). This rise in FSH concentration was accompanied by a significant (P < 0.001) rise in the total number of follicles > 2.0 mm per ovary in both immunized groups (inhibin-immunized 5.5 +/- 1.0 to 13.6 +/- 1.4; oestradiol-immunized 4.6 +/- 0.5 to 11.5 +/- 1.0).(ABSTRACT TRUNCATED AT 250 WORDS)

Active immunization of Merino ewe lambs with recombinant bovine alpha inhibin advances puberty and increases ovulation rate

Ewe lambs (n = 24-25) were immunized at 3, 7 and 15 weeks of age with recombinant bovine alpha-inhibin (rec inhibin) or with bovine monoclonal antibody purified inhibin (bMPI) obtained by immunochromatography from bovine follicular fluid or with adjuvant alone (control). Antibodies in the plasma of the lambs immunized with the inhibin preparations bound to iodinated 31 kDa bovine inhibin. Binding was minimal after the primary immunization, increased after each booster immunization and remained elevated until at least 45 weeks of age (29% for rec inhibin and 11% for bMPI). Of the group treated with rec inhibin, 10 ovulated as lambs (control 0/22; bMPI 3/21) and onset of overt oestrous activity (as hoggets) was advanced (P < 0.05) by 17 days in lambs immunized with rec inhibin. As hoggets, the ovulation rate was greater (P < 0.01) in the rec inhibin immunized lambs (4.41 +/- 0.67) than in the control animals (1.27 +/- 0.15) but not in the bMPI-treated lambs (1.40 +/- 0.16). After a further immunization at 17 months of age, however, ovulation rate increased (P < 0.01) in the bMPI-immunized group (3.40 +/- 0.47) but was unchanged in the lambs immunized with rec inhibin (2.80 +/- 0.52) and those in the control group (1.15 +/- 0.08). There were no effects of immunization on plasma concentrations of either follicle stimulating hormone (FSH) or luteinizing hormone (LH). The initial smaller response seen with the bMPI may be due to either the presence of compounds other than inhibin in such preparations or the small absolute amount of inhibin injected.(ABSTRACT TRUNCATED AT 250 WORDS)

The relationship between peripheral immunoactive inhibin, human chorionic gonadotrophin, oestradiol and progesterone during human pregnancy

OBJECTIVE

The objective of this study was to investigate serial changes in the plasma concentration of inhibin in both the very early days of pregnancy following implantation and in late pregnancy. The timing of the changes in inhibin concentration relative to changes in the concentrations of other hormones of pregnancy was also investigated.

DESIGN

Serial observations of the peripheral concentrations of inhibin and other hormones in two groups of healthy volunteers in (a) early pregnancy and (b) late pregnancy.

PATIENTS

(a) Four healthy women recruited on cessation of contraception prior to conception. (b) Nine healthy women recruited at the antenatal clinic.

MEASUREMENTS

In the early pregnancy subjects, the concentrations of inhibin, progesterone, oestradiol and hCG were measured in plasma samples obtained three times per week from day 8 to day 10 of each menstrual cycle until 11 weeks after the last menstrual period in the conception cycle. In the late pregnancy subjects, plasma samples were obtained at 4-week intervals from 12 weeks until term.

RESULTS

The concentration of inhibin, progesterone and oestradiol in conception cycles were similar to those in the preceding cycles until the mid/to late-luteal phase of the cycle when hCG was first measureable. By day 12 of the luteal phase the concentration of inhibin was significantly higher in the pregnancy cycle than in the non-pregnancy cycle (P < 0.05) and progressively increased after the time of the missed menstrual period. The concentration of inhibin reached a peak (513.0 U/l, CI 442.1-595.3) by day 47 when the concentration of hCG was maximal. In early pregnancy the concentration of inhibin was correlated with that of hCG (r = 0.361; P < 0.01) as well as progesterone (r = 0.584, P < 0.001) and oestradiol (r = 0.602, P < 0.001). After 12 weeks there was no significant correlation between hCG and inhibin although significant correlations persisted with progesterone (r = 0.553, P < 0.001) and oestradiol (r = 0.361, P < 0.01).

CONCLUSIONS

The corpus luteum makes a significant contribution to the production of inhibin in early pregnancy while after 12 weeks the placenta is the major source.

Evidence that inhibin is an important factor in the regulation of FSH secretion during the mid-luteal phase in cows

To investigate the physiological importance of inhibin in the regulation of FSH secretion in cows, seven cyclic cows were treated with an inhibin antiserum raised against bovine 32 kDa inhibin in a castrated goat. The same animals treated with a castrated goat serum (control serum) served as controls. On day 12 of the oestrous cycle (day 0 = day of oestrus), four of seven cows were injected with 100 ml inhibin antiserum first, and the remaining three cows with 100 ml control serum first. Twelve days after the second oestrus following the first serum injection (42-46 days after the first serum injection), the former four cows were injected with control serum and the latter three with inhibin antiserum. Follicular development after the injections of control serum or inhibin antiserum was assessed by daily ultrasonographic examination. Treatment with inhibin antiserum resulted in a marked increase (P < 0.01) in plasma concentrations of FSH and oestradiol-17 beta but not LH or progesterone, compared with those after treatment with control serum. Plasma concentrations of FSH increased significantly (P < 0.01) at 8 h after injection of anti-inhibin serum when compared with the control value. Concentrations of FSH in the plasma remained high for 72 h, then declined to the control level by 84 h, concomitant with an abrupt decrease in the titre of free inhibin antibody in the plasma. High concentrations of oestradiol-17 beta were observed between 36 and 96 h after treatment.(ABSTRACT TRUNCATED AT 250 WORDS)