Comparison of the effects of crude and highly purified bovine inhibin (Mr 32,000) on plasma concentrations of FSH and LH in chronically ovariectomized prepubertal heifers

Inherent capacity of the pituitary gland to produce gonadotropins is not influenced by the number of ovarian follicles > or = 3 mm in diameter in cattle

We hypothesised that higher serum FSH concentrations in cattle with low v. high follicle numbers during follicular waves are caused by a different capacity of the pituitary gland to produce gonadotropins. Dairy cows with high (> or = 30; n = 5) and low (< or = 15; n = 5) follicle numbers were selected and serum concentrations of oestradiol and FSH during an oestrous cycle were measured. Cows were ovariectomised at oestrus and bled frequently up to 8 days after ovariectomy. After 33 days, cows were injected with gonadotropin-releasing hormone (GnRH) and bled intensively up to 8 h after GnRH injection. One day later, animals were injected with follicular fluid (FF) from bovine follicles and were bled intensively up to 2 days after the first injection. Serum concentrations of FSH and LH were measured. After 2 days, cows were killed and their pituitary glands collected. Prior to ovariectomy, serum oestradiol concentrations were similar between groups, whereas FSH concentrations were higher in cattle with low v. high numbers of follicles. No differences were detected in serum gonadotropin concentrations after ovariectomy, GnRH injection or FF challenge between groups. The results indicate that the inherent capacity of the pituitary gland to secrete gonadotropins does not differ between cattle with high v. low numbers of follicles during follicular waves.

Reproductive Hormones and Follicular Growth During Development of One or Multiple Dominant Follicles in Cattle1

The mechanisms regulating ovulation rate under natural conditions are not yet defined, particularly for monovular species. In the present study, we evaluated ovarian structures (every 12 h by ultrasonography) and circulating hormones (every 6 h) to determine the differences between cows that developed one (single dominant; n = 16), two (double dominant; n = 8), or three (triple dominant; n = 3) dominant follicles. The four largest follicles were tracked retrospectively, and the data were normalized to the time of expected follicular deviation (F1 >/= 8.5 mm; hour 0). Follicular dynamics from emergence to deviation were similar, whereas after deviation, expected subordinate follicles continued to grow at a rate similar to the dominant follicle. Triple dominants had greater FSH than double dominants (hour -24 to hour -12) and single dominants (hour -42 to hour -6), and double dominants had greater FSH than single dominants (hour -24 to hour -12). Increased circulating estradiol but lower inhibin were observed in cows that developed multiple follicles. In addition, double dominants had greater LH than single dominants (hour -42 to hour -24 and hour -6 to hour 0) and lower progesterone than single dominants (hour -12 and hour -6). Luteal volume was similar between groups, but milk production was greater for codominant than for single-dominant cows. Thus, selection of multiple dominant follicles during high milk production is related to a transient increase in circulating FSH and LH during the 24 h before follicular selection, producing continued postdeviation growth of follicles that ordinarily would have regressed. Increased FSH and LH probably result from decreased circulating inhibin and progesterone in cows that develop codominant follicles.

Active immunization against inhibin improves superovulatory response to exogenous FSH in cattle

The effect of active immunization against inhibin on the response to superovulatory treatment by porcine FSH (pFSH) was investigated in cattle. Japanese black cows were sc injected with 1 mg of porcine inhibin alpha-subunit fragment (1-26) conjugated with rabbit serum albumin (inhibin-immunized group; n=14) or rabbit serum albumin alone (control group; n=12) in Freund's complete adjuvant. Booster injections (half the amount of the primary injection) were given 35 and 70 days after the primary injection. All cows were superovulated three times with pFSH. Three days after each injection of the antigen, a progesterone-releasing intravaginal device (CIDR-B) was inserted vaginally into all animals and left in place for 10 days. Forty-eight hours before CIDR-B removal, all animals were sc injected with 30 mg pFSH dissolved in 40% polyvinylpyrrolidone, and im injected with 750 microg of PGF2alpha at CIDR-B removal. Cows were artificially inseminated twice during estrus, and ova or embryos were collected 7 or 8 days after estrus. The number of corpora lutea, the number of ova or embryos and the number of transferable embryos in inhibin-immunized cows (12.1+/-1.2, 11.1+/-1.3 and 6.2+/-1.0, respectively) were significantly greater than those in the controls (8.2+/-1.0, 5.7+/-1.1 and 3.1+/-0.7, respectively). These results indicate that active immunization against inhibin enhanced ovarian response to the usual superovulatory treatment in cattle. Therefore, immunization against inhibin may be a useful approach for improving the response to superovulation in cattle.

Plasma concentrations of inhibin A in cattle with follicular cysts: relationships with turnover of follicular waves and plasma levels of gonadotropins and steroid hormones

We investigated the profiles of circulating levels of inhibin A and total inhibin in beef cows with follicular cysts in relation to the patterns of follicular development and circulating gonadotropins and steroid hormones. Turnover of follicular waves was monitored in five cows every 2 days for 70 days from 10 days after detection of estrus without ovulation. The mean interwave intervals were 19.6 +/- 1.0 days (n = 18 waves with cysts from the five cows). Circulating levels of inhibin A were approximately 170 pg/ml before emergence of follicular waves with cysts and increased (P < 0.05) concomitantly with follicle emergence. High concentrations of inhibin A (greater than 300 pg/ml) were noted for 7 days during the growth phase of cystic follicles, but inhibin A levels decreased gradually when development of the cysts reached a plateau. This profile of inhibin A was similar to those of total inhibin and estradiol, but was inversely related to the changes in plasma FSH concentrations. LH pulse frequency and mean concentrations of LH in cows with cysts were higher than those observed in the luteal phase of normal cyclic cows. These results indicate that the capacity to secrete inhibin, as well as estradiol, is maintained in cystic follicles, the growth of which is extended by LH secretion at levels greater than those seen in the normal luteal phase. Inhibin A plays an important role in the extension of interwave intervals by suppressing recruitment of a new cohort of follicles.

Effects of re-immunization of heifers against inhibin on hormonal profiles and ovulation rate

To study the effect of re-immunization against inhibin on ovarian response and hormonal profiles, Japanese beef heifers (n = 5) were re-immunized three times with inhibin vaccine (recombinant ovine inhibin α-subunit in oil emulsion, 125 μg ml−1) one year after the primary immunization. Control heifers (n = 5) were injected with placebo (Montanide: Marcol adjuvant alone). Oestrous cycles were synchronized by using prostaglandin F2α (PGF2α) and ovarian response was monitored daily by ultrasonography. Blood samples were collected by jugular venipuncture for assessment of hormonal levels and inhibin antibody titres. In contrast to controls, inhibin re-immunized heifers generated antibodies against inhibin rapidly reaching a peak level 9 days after the first booster injection. The mean concentrations of FSH in re-immunized cows increased significantly in comparison with controls. In addition, there was a significant increase in oestradiol-17β and progesterone levels in re-immunized cows compared with controls. Inhibin re-immunized heifers had a significant increase in small (≥4 < 7 mm), medium (≥7 < 10 mm) and large (≥10 mm in diameter) sized follicles. Moreover, the mean ovulation rate was 5.0 ± 1.1 after the third booster injection in re-immunized heifers compared with control heifers (single ovulation). These results clearly demonstrate that re-immunization of inhibin can be used to enhance ovarian follicular development and ovulation rate. Furthermore, the great number of follicles is a potential source of oocytes that could be harvested for in vitro fertilization and embryo transfer programmes.

The effect of different doses of Gonadorelin on ovarian follicle dynamics in river buffalo (Bubalus bubalis)

The objective of this study was to determine the response of the ovarian dominant follicle to the different doses of GnRH in river buffalo. The estrous cycle of 12 river bufflaloes was synchronized using norgestomet implant for 12 days in association with two injections of prostaglandin F2alpha analogue on Days 0 and 7 of implant insertion. On Day 6 or 7 of the ensuing cycle (Day 0 of the experiment), females received a norgestomet implant in conjunction with two prostaglandin injections on Days 0 and 1. On Day 6 of the experiment, females were randomly allocated into three groups. At this time, Group 1 and 2 females were given an i.m. injection of 50 or 100 microg Gonadorelin, respectively. Group 3 females did not receive any further treatment and were considered as control. All females were given prostaglandin on Day 12 and implants were removed on Day 13 of the experiment. The results revealed that in the control group, ovarian dominant follicle became persistent throughout the experiment; whereas, the persistent dominant follicle in all females belonging to Group 2 (100 microg GnRH) and one female in Group 1 (50 microg GnRH) ovulated within 48 h, subsequent with an emergence of a new follicular wave and an increase in plasma progesterone concentration within 72 and 96 h after GnRH injection, respectively. In conclusion, 100 microg of Gonadorelin seems to be the most effective dose to induce ovulation followed by an emergence of a new follicular wave in river buffalo.

Follicle wave growth in cattle

Ovarian follicle growth in cattle culminates in the selection of a single dominant follicle which attains the ability for final maturation and ovulation once or twice during the luteal phase and at the end of the oestrous cycle, as well as during other reproductive states. This review will describe in detail the first follicle wave of the cycle leading to selection of the first wave dominant follicle, indicating the specific gonadotrophin dependencies of cohort and dominant follicles, and relating follicle fate to steroidogenesis. As a differential gonadotrophin response of growing antral follicles during the follies-stimulating hormone (FSH) decline may determine which follicle becomes selected, first wave follicles are also characterized in relation to intrafollicular growth factors, which may modify the gonadotrophin response, such as inhibins and members of the insulin-like growth factor (IGF) family. Subsequently, the follicular control of the transient FSH rise and decline so crucial to dominant follicle selection will be discussed. It is concluded that successful hormonal manipulation of follicle wave growth and dominant follicle selection will depend on our detailed understanding of the gonadotrophin requirements of differentiating wave follicles.

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

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

Plasma inhibin A in heifers: relationship with follicle dynamics, gonadotropins, and steroids during the estrous cycle and after treatment with bovine follicular fluid

The relationship between follicle growth and plasma inhibin A, FSH, LH, estradiol (E), and progesterone was investigated during the normal bovine estrous cycle and after treatment with steroid-free bovine follicular fluid (bFF) to arrest follicle development. In the first study, four heifers were monitored over three prostaglandin (PG)-synchronized cycles. Blood was collected every 2-8 h, and ovaries were examined daily by ultrasonography. Inhibin A was measured using a modified enzyme-linked immunosorbent assay that employed a new monoclonal antibody against the alpha subunit of bovine inhibin. Plasma inhibin A ( approximately 50 pg/ml before luteolysis) rose steadily during the induced follicular phase (P < 0.05) to a peak ( approximately 125 pg/ml) coincident with the preovulatory E/LH/FSH surge. After ovulation, inhibin A fell sharply (P < 0.05) to a nadir ( approximately 55 pg/ml) coincident with the secondary FSH rise. During the next 3 days, inhibin A increased to approximately 90 pg/ml in association with growth of the new dominant follicle (DF). Plasma E also rose twofold during this period, whereas FSH fell by approximately 50%. Inhibin A was negatively correlated with FSH (r = -0.37, P < 0.001) and positively correlated with E (r = 0.49, P < 0.0001). Observations on eight cycles (two cycles/heifer), in which growth of the ovulatory DF was monitored from emergence to ovulation, showed that the first-wave DF (DF1) ovulated in three cycles and the second-wave DF (DF2) in five cycles. After PG, plasma inhibin A and E increased similarly in both groups, with concomitant falls in FSH. In the former group, the restricted ability of DF1 to secrete both inhibin A and E was restored after luteolysis. Results indicate that dynamic changes in the secretion of both E and inhibin A from the DF contribute to the fall in FSH during the follicular phase and to the generation and termination of the secondary FSH surge, both of which play a key role in follicle selection. In the second study, bFF (two dose levels) was administered to heifers (n = 3-4) for 60 h starting from the time of DF1 emergence. Both doses suppressed FSH (P < 0.05) and blocked DF1 growth to the same extent (P < 0.01), although inhibin A levels were only marginally raised by the lower dose (not significant compared to controls). The high bFF dose raised (P < 0.001) inhibin A to supraphysiological levels ( approximately 1 ng/ml). A large "rebound" rise in FSH occurred within 1 day of stopping both treatments, even though the inhibin A level in the high-dose bFF group was still approximately threefold higher than that in controls. This indicates that desensitization of gonadotropes to inhibin negative feedback is a contributory factor, together with reduced ovarian output of E, in generation of the post-bFF rebound in FSH.

Effects of follicle-stimulating hormone with and without luteinizing hormone on serum hormone concentrations, follicle growth, and intrafollicular estradiol and aromatase activity in gonadotropin-releasing hormone-immunized heifers

To evaluate the roles of FSH and LH in follicular growth, GnRH-immunized anestrous heifers (n = 17) were randomly assigned (Day 0) to one of three groups (n = 5 or 6). Group 1 received i.m. injections of 1.5 mg porcine FSH (pFSH) 4 times/day for 2 days; group 2 received i.v. injections of 150 microg pLH 6 times/day for 6 days; group 3 received both pFSH and pLH as described for groups 1 and 2. After slaughter on Day 6, measurements were made of follicle number and size, and follicular fluid concentrations of progesterone (P(4)), estradiol (E(2)), and aromatase activity. Injection of pFSH increased (P: < 0.01) the serum concentrations of FSH between 12 and 54 h. Infusion of pLH increased (P: < 0.05) mean and basal concentrations of LH and LH pulse frequency. Serum E(2) concentrations were higher (P: < 0.05) for heifers given pFSH + pLH than those given either pFSH or pLH alone. There was no difference (P: > or = 0.24) between treatments in the number of small follicles (<5 mm). Heifers given pFSH or pFSH + pLH had more (P: < or = 0.02) medium follicles (5.0-9.5 mm) than those that were given pLH alone (none present). Heifers given pFSH + pLH had more (P: = 0.04) large follicles (> or =10 mm) than those given either pLH or pFSH alone (none present). Overall, only 1 of 35 small follicles and 2 of 96 medium follicles were E(2)-active (i.e., E(2):P(4) >1.0), whereas 18 of 21 large follicles (all in the pFSH + pLH treatment) were E(2)-active; of these, 8 of 18 had aromatase activity. Concentrations of E(2) and E(2) activity in follicular fluid were correlated (r > or = 0.57; P: < 0.0001) with aromatase activity in heifers given pLH + pFSH. In conclusion, pLH failed to stimulate follicle growth greater than 5 mm; pFSH stimulated growth of medium follicles that were E(2)-inactive at slaughter and failed to increase serum E(2) concentrations; whereas pFSH + pLH stimulated growth of medium follicles and E(2)-active large follicles, and a 10- to 14-fold increase in serum E(2) concentrations.

Follicle selection in cyclic guinea pigs with active immunization against inhibin alpha-subunit

Experiments were conducted to elucidate the mechanisms of active immunization against inhibin on ovarian follicular development and selection in guinea pigs. Estrous cycle was synchronized in experimental guinea pigs by implanting progesterone containing tubes. Antibodies that bound 125I-labeled bovine inhibin were produced by all guinea pigs receiving the inhibin vaccine (recombinant ovine alpha-subunit in oil emulsion) without any effects on duration of the estrous cycle. Active immunization against inhibin increased the plasma concentrations of progesterone during the luteal phase and the plasma concentrations of estradiol but failed to increase the plasma concentration of follicle-stimulating hormone (FSH) during preovulatory period. The treatment also increased the number of corpora lutea (from 1.3+/-0.3 to 7.0+/-1.6 per each ovary), and preovulatory sized follicles (from 1.8+/-0.6 to 7.0+/-1.6 per each ovary), and follicles stained positively for inhibin alpha-subunit (from 2.3+/-0.5 to 6.3+/-1.3 per each ovary) significantly. The results indicate that active immunization against inhibin enhances ovulation rate by affecting the follicle selection and only dominant follicle can be stained for inhibin alpha-subunit in guinea pigs. This study is firstly to provide direct evidence that inhibins play important role in follicle selections in guinea pigs.

Synchronization of ovulation in beef cows (Bos indicus) using GnRH, PGF2alpha and estradiol benzoate

The objective of this study was to evaluate protocols for synchronizing ovulation in beef cattle. In Experiment 1, Nelore cows (Bos indicus) at random stages of the estrous cycle were assigned to 1 of the following treatments: Group GP controls (nonlactating, n=7) received GnRH agonist (Day 0) and PGF2alpha (Day 7); while Groups GPG (nonlactating, n=8) and GPG-L (lactating, n=9) cows were given GnRH (Day 0), PGF2alpha (Day 7) and GnRH again (Day 8, 30 h after PGF2alpha). A new follicular wave was observed 1.79+/-0.34 d after GnRH in 19/24 cows. After PGF2alpha, ovulation occurred in 19/24 cows (6/7 GP, 6/8 GPG, 7/9 GPG-L). Most cows (83.3%) exhibited a dominant follicle just before PGF2alpha, and 17/19 ovulatory follicles were from a new follicular wave. There was a more precise synchrony of ovulation (within 12 h) in cows that received a second dose of GnRH (GPG and GPG-L) than controls (GP, ovulation within 48 h; P<0.01). In Experiment 2, lactating Nelore cows with a visible corpus luteum (CL) by ultrasonography were allocated to 2 treatments: Group GPE (n=10) received GnRH agonist (Day 0), PGF2alpha (Day 7) and estradiol benzoate (EB; Day 8, 24 h after PGF2alpha); while Group EPE (n=11), received EB (Day 0), PGF2alpha (Day 9) and EB (Day 10, 24 h after PGF2alpha). Emergence of a new follicular wave was observed 1.6+/-0.31 d after GnRH (Group GPE). After EB injection (Day 8) ovulation was observed at 45.38+/-2.03 h in 7/10 cows within 12 h. In Group EPE the emergence of a new follicular wave was observed later (4.36+/-0.31 d) than in Group GEP (1.6+/-0.31 d; P<0.001). After the second EB injection (Day 10) ovulation was observed at 44.16+/-2.21 h within 12 (7/11 cows) or 18 h (8/11 cows). All 3 treatments were effective in synchronizing ovulation in beef cows. However, GPE and, particularly, EPE treatments offer a promising alternative to the GPG protocol in timed artificial insemination of beef cattle, due to the low cost of EB compared with GnRH agonists.

Relationship between follicular development and the decline in the follicle-stimulating hormone surge in heifers

Experiment 1 was conducted to determine whether progesterone affects the pattern of the FSH surge or follicular development associated with a follicular wave in heifers. On Day 7 (Day 0 = ovulation), heifers were allocated into a group receiving prostaglandin F2alpha (PGF2alpha; n = 6) or a control group (n = 5). Twenty-four hours later, all detectable follicles (>/= 2 mm) were ablated (Hour 0). Follicular development was monitored Hours 0, 3, 6, 9, 12, and 16, at 8-h intervals thereafter until Hour 112. To monitor FSH concentrations, blood was sampled at Hours -24, 0, 3, 6, 9, 12, and 16, and at 8-h intervals thereafter until Hour 104. There were no differences (p > 0.05) between the PGF2alpha-treated group and controls in the patterns of the FSH surge or follicular development. Experiment 2 tested the hypothesis that 3-mm follicles do not have FSH-suppressing capacity and that suppression increases as follicles grow beyond 5 mm. Twenty-four hours after an injection of PGF2alpha (Days 6-8), heifers were subjected to either ablation of follicles >/= 2 mm or ovariectomy. Intact heifers were allocated into four groups (n = 5) in which all follicles of the new wave were ablated upon reaching either 3, 5, or 7 mm or were not ablated (controls). Blood was sampled at 8-h intervals to monitor FSH and estradiol-17beta. Averaged over Hours 8-120, FSH concentrations (ng/ml) were higher (p < 0.05) in the ovariectomized (2.02 +/- 0.05) and the 3-mm groups (1.91 +/- 0.05) than in the 5-mm (1.52 +/- 0.05), 7-mm (1.35 +/- 0.04), and control groups (1.33 +/- 0.05); and estradiol concentrations (pg/ml) were lower (p < 0.05) in the ovariectomized group (0.19 +/- 0.03) than in the 3-mm (1.48 +/- 0. 16), 5-mm (1.56 +/- 0.15), 7-mm (2.22 +/- 0.27), and control groups (2.55 +/- 0.49). In conclusion, the presence of endogenous progesterone did not affect FSH patterns or follicular development. Follicles </= 3 mm had no detectable capacity to suppress FSH. As follicles grew from 3 to 5 mm, they gained the capacity to suppress FSH; however, as follicles grew beyond 5 mm, FSH-suppressing capacity did not increase. The FSH decline was not attributable to an increase in circulating estradiol.

Ovarian response and FSH profile in cows following injection of various doses of inhibin antiserum

Dose effect of inhibin antiserum on ovarian response and hormonal profiles were investigated. On day 12 of the estrous cycle (day 0 = estrus), 14 of 19 cows were given a single i.v. injection of 25 ml (n = 4), 37.5 ml (n = 5) or 50 ml (n = 5) antiserum against inhibin produced in a castrated male goat. The other 5 animals were given 50 ml castrated male goat serum (control serum). The animals in each group received a single i.m. injection of 0.5 mg prostaglandin F2 alpha analogue (PG) 48 hr following the serum injection. The population of follicles and ovulation rate (estimated by the number of corpora lutea) were examined by ultrasonography. Administration of inhibin antiserum consistently resulted in a significant (p < 0.01) increase in plasma concentrations of follicle-stimulating hormone (FSH) in inhibin-neutralized groups, although the increased FSH levels were sustained longer in 50-ml group than in the 25- and 37.5- ml groups. Levels in the circulating inhibin antibody titer were positively correlated with dosage of inhibin antiserum. A large number of antral follicles (> or = 4 mm in diameter) developed similarly after hypersecretion of FSH in all neutralized groups, coupled with a rise in plasma estradiol levels, while the number of large follicles (> or = 10 mm in diameter) on estrus showed a dose-dependent increase. Multiple ovulation (2 to 4) was recorded in all animals after injection of 50 ml inhibin antiserum, however all cows in the 25-ml group experienced only one ovulation and injection of 37.5 ml resulted in a variable number of ovulations (1 to 5). These results demonstrated that administration of inhibin antiserum on day 12, followed by injection of PG, was able to induce hypersecretion of FSH and subsequently multiple ovulations. The number of large follicles on estrus day and ovulations were affected by dosage of inhibin antiserum and were correlated with persistence of increased FSH levels or circulating antibody levels.

Effects of passive immunization against inhibin on ovulation rate and embryo recovery in holstein heifers

The effects of acute neutralization of endogenous inhibin on ovulation rate and circulating FSH levels were investigated. Nine or ten days after estrus, 5 heifers were given a single injection of 75 ml iv inhibin antiserum produced in a castrated male goat, while another 5 were given the same amount of a castrated male goat serum. All heifers were given injections of PGF2alpha im at 48 h and 60 h after the serum injection. Those exhibiting an estrus were artificially inseminated with frozen-thawed semen. Seven or eight days after the insemination, ova or embryos were collected using a non-surgical method. Administration of inhibin antiserum resulted in a significant increase in the number of medium-sized follicles compared with the number in the control animals. The number of large follicles in the inhibin-neutralized animals was 4.8 +/- 2.4 (mean +/- SEM; n = 5) on the day of estrus, while there was a single large follicles in the ovaries of control animals. Seven or eight days after estrus, 3 to 16 ova or embryos were recovered from 4 of 5 animals, and 64 % of the total ova/embryos were transferable. Administration of inhibin antiserum produced a significant increase in the concentrations of plasma FSH from 12 to 72 h after the serum injection compared with the levels in the control animals (P < 0.05). After the onset of estrus, preovulatory LH and FSH surges were noted in inhibin-neutralized animals and magnitude of the rise in each hormone was similar to the control animals. The present study demonstrates that a single injection of the inhibin antiserum induces multiple ovulations probably by enhancing FSH secretion, and that recovery of embryos is equal to that observation after an ordinary FSH treatment.

Follicular function in lactating dairy cows treated with sustained-release bovine somatotropin

The objective of this study was to determine the long-term, short-term, and residual effects of bovine somatotropin (bST) on ovarian function. Twenty-six Holstein cows were assigned to one of four groups and given either bST (500 mg) or saline for seven injection cycles (14 d between injections). Groups were 1) seven injection cycles of saline (control), 2) seven injection cycles of bST, 3) three injection cycles of bST followed by four injection cycles of saline, and 4) three injection cycles of saline followed by four injection cycles of bST. Beginning in the middle of the fourth injection cycle, an estrous cycle was synchronized for study. Serum concentrations of bST and insulin-like growth factor I were lowest during saline injections and increased after bST injections. Growth of the first wave dominant follicle was similar; however, start of the second follicular wave was approximately 48 h earlier in those cows treated with bST (groups 2, 3, and 4). Cows treated with somatotropin had a similar pattern of follicular growth, but tended to have more class 1 (3 to 5 mm) follicles and had more class 2 (6 to 9 mm) follicles than did the control cows. Peak concentrations of serum FSH were lower and occurred earlier for the cows treated with bST. There were no differences in the long-term or short-term effects of bST on ovarian function. Furthermore, cows that were switched from bST to saline (group 3) showed a residual effect of bST for up to 3 wk.

Production of immunoactive inhibin by bovine granulosa cells in serum-free culture: effects of exogenous steroids and FSH

Granulosa cells from pooled bovine follicles were cultured under chemically-defined (serum-free) conditions to study the effects of exogenous steroids and FSH on production of immunoactive (ia) inhibin, oestradiol and progesterone. Levels of ia-inhibin in media samples and cell lysates were measured by radioimmunoassay (RIA) using an antiserum raised against a synthetic fragment of human inhibin alpha-subunit [hI alpha (1-32)]. Cells secreted measurable amounts of ia-inhibin, oestradiol and progesterone for at least 7 d of culture, although intracellular levels of inhibin were very low, indicating that newly-synthesized ia-inhibin is rapidly released from the cells. Treatment with androstenedione (0.2 mumol/l) or testosterone (0.2 mumol/l) increased ia-inhibin secretion markedly; levels on Day 5 of culture were approximately 6-fold (P < 0.005) higher than control values. In contrast, treatment with the non-aromatizable androgen dihydrotestosterone (DHT; 0.2 mumol/l) resulted in only a one- to two-fold increase (P < 0.05) over control values (Day 5). Addition of exogenous oestradiol (8 nmol/l) markedly increased ia-inhibin secretion (8-9 fold on Day 5; P < 0.05) compared with basal levels, whereas progesterone had no effect. Secretion of oestradiol, undetectable in the absence of exogenous androgens, rose daily in the presence of either androstenedione or testosterone, levels rising approximately 6-fold and 9-fold respectively over a 4-d treatment period. Progesterone secretion increased approximately 2-fold over the culture period and was unaffected by any steroid treatment. Treatment with ovine FSH (10ng/ml) alone stimulated secretion of progesterone over basal levels (3-fold higher on Day 6; P < 0.005), but did not affect output of either ia-inhibin or oestradiol. However, exposure to FSH in the presence of androstenedione not only promoted a further 4-fold increase in progesterone output but also led to a dose-dependent suppression of both ia-inhibin (approximately 90% lower on Day 6; P < 0.001) and oestradiol (approximately 80% lower on Day 6; P < 0.001) secretion compared to cells treated with androstenedione alone. These observations indicate that the secretion of ia-inhibin by bovine granulosa cells in culture is positively regulated by oestradiol, implying an autocrine/paracrine role for this hormone in control of ovarian inhibin production. The ability of aromatizable androgens to stimulate secretion of inhibin, coupled with the inability of the non-aromatizable androgen DHT to elicit such an effect, suggests that inhibin output is largely unaffected by androgens prior to their conversion to oestradiol.(ABSTRACT TRUNCATED AT 400 WORDS)

Control of FSH, follicular development and estrus synchronization in the mare with steroid-free follicular fluid

Twenty-two pony mares were used in a project designed to determine the effectiveness of different treatments in controlling FSH, follicular development and synchronization of estrus and ovulation. Mares in Group 1 (n=8) received daily oral altrenogest (0.044 mg/kg); those in Group 2 (n=7) received daily altrenogest (0.044 g/kg) and, during the last 4 days of treatment they received steroid-free follicular fluid, (15 cc) intravenously (I.V.) two times a day; Mares in Group 3 (n=7) received daily intramuscular (I.M.) injections of progesterone (80 mg) and estradiol valerate (7 mg). All treatments lasted for 10 days, at the end of which prostaglandin (PgF(2)alpha, 10 mg) was administered. Sexual behavior, follicular development and FSH concentrations were monitor daily. Concentrations of FSH in Group 2 mares, were not significantly different (P>0.05) from those of Group 1 until the mares in Group 2 were treated with follicular fluid (P<0.05). Concentrations of FSH in Group 3 mares, were significantly lower than those of Groups 1 and 2 (P<0.05) until the mares in Group 2 were treated with steroid-free follicular fluid. At this point there was no significant difference between groups 2 and 3 (P>0.05). Steroid-free follicular fluid appears to induce atresia in larger follicles (>11 mm), and the initiation of new follicular wave. The combination of progesterone and estradiol valerate appears to delay follicular growth and not to induce atresia, since larger follicles (>11 mm) continued to grow after treatment. Both treatments (groups 2 and 3) resulted in ovulations within 5 days period. The treatment in Group 1 did not have any effect on FSH or follicular development and ovulations were dispersed through a 9-day period. We concluded that steroid-free follicular fluid offers a new possibility to synchronize ovulation in the mare by controlling FSH and follicular development.

Expression of bovine inhibin beta subunit in Escherichia coli

1. A DNA fragment encoding the beta subunit of bovine inhibin was amplified using the polymerase chain reaction and was cloned in plasmids pUC8 and pUR291. 2. Cultures of Escherichia coli TG2 harbouring pKDK37, a pUR291-derived recombinant plasmid, produced a novel protein with a molecular weight of 130,000 corresponding to a beta-galactosidase-inhibin beta fusion protein. 3. The fusion protein was purified from inclusion bodies by solubilization in 8 M urea followed by an ion-exchange and gel permeation chromatography. 4. Analysis by immunoblotting and competitive radioimmuno assay revealed that the fusion protein was recognized by a monoclonal antibody raised against a chemically synthesized peptide for amino acid residues from +82 to +114 of the beta subunit of the bovine inhibin thereby confirming its identity.