Effects of immunization against recombinant bovine inhibin alpha subunit on circulating concentrations of gonadotrophins in ewes

Inhibin Inactivation in Female Mice Leads to Elevated FSH Levels, Ovarian Overstimulation, and Pregnancy Loss

Inhibins are members of the transforming growth factor-β family, composed of a common α-subunit disulfide-linked to 1 of 2 β-subunits (βA in inhibin A or βB in inhibin B). Gonadal-derived inhibin A and B act in an endocrine manner to suppress the synthesis of follicle-stimulating hormone (FSH) by pituitary gonadotrope cells. Roles for inhibins beyond the pituitary, however, have proven difficult to delineate because deletion of the inhibin α-subunit gene (Inha) results in unconstrained expression of activin A and activin B (homodimers of inhibin β-subunits), which contribute to gonadal tumorigenesis and lethal cachectic wasting. Here, we generated mice with a single point mutation (Arg233Ala) in Inha that prevents proteolytic processing and the formation of bioactive inhibin. In vitro, this mutation blocked inhibin maturation and bioactivity, without perturbing activin production. Serum FSH levels were elevated 2- to 3-fold in InhaR233A/R233A mice due to the loss of negative feedback from inhibins, but no pathological increase in circulating activins was observed. While inactivation of inhibin A and B had no discernible effect on male reproduction, female InhaR233A/R233A mice had increased FSH-dependent follicle development and enhanced natural ovulation rates. Nevertheless, inhibin inactivation resulted in significant embryo-fetal resorptions and severe subfertility and was associated with disrupted maternal ovarian function. Intriguingly, heterozygous Inha+/R233A females had significantly enhanced fecundity, relative to wild-type littermates. These studies have revealed novel effects of inhibins in the establishment and maintenance of pregnancy and demonstrated that partial inactivation of inhibin A/B is an attractive approach for enhancing female fertility.

Immunization Against Inhibin Promotes Fertility in Cattle: A Meta-Analysis and Quality Assessment

Superovulation and embryo transfer techniques are important methods in cattle breeding. Combined with traditional superovulation protocols, immunization against inhibin can further improve follicular development and embryo yield. The aim of this study is to determine the efficacy of immunization against inhibin in improving the fertility of cattle through meta-analysis and to provide better clinical veterinary practice guidance. Three English databases (PubMed, EMBASE, Web of Science) were searched for research articles of immunizations against inhibin influence on cattle fertility. Literature screening, data extraction, and meta-analysis were conducted in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. In addition, the Systematic Review Center for Laboratory animal Experimentation (SYRCLE) risk-of-bias (RoB) tool was used to assess the risk of bias of the included animal studies. Potentially relevant studies (317) were identified, and finally 14 eligible studies (all in English) were included. The results of meta-analysis revealed that immunization against inhibin has significant effects on improving the number of ovulations [mean difference (MD) = 0.44, 95% confidence interval (CI) = (0.31, 0.56)], embryos and unfertilized ova [MD = 4.51, 95% CI = (2.28, 6.74)], follicles of the three size categories, the incidence of multiple ovulations [OR = 22.50, 95% CI = (8.13, 62.27)], and the conception rate [OR = 2.36, 95% CI = (1.26, 4.40)]. Moreover, it improved the production of embryos [grades 1 embryos: MD = 3.84, (3.54, 4.15); grade 2 embryos: MD = -0.73, (-0.89, -0.57); grade 3 embryos: MD = -0.50, (-0.75, -0.25); degenerated embryos: MD = 1.16, (-0.51, 2.82); transferable embryos: MD = 2.67, (2.03, 3.31)] and the number of corpora lutea [MD = 1.25, 95% CI = (0.79, 1.71)]. In the above indicators, the differences between the two groups were statistically significant (all p < 0.0001). Additionally, according to the quality evaluation results, the risk of bias in the included studies is relatively high. The quality evaluation of the results of the included studies showed that the risk of bias mainly concentrated in the selective, performance, detection, and reporting of bias aspects.

'Free' inhibin α subunit is expressed by bovine ovarian theca cells and its knockdown suppresses androgen production

Inhibins are ovarian dimeric glycoprotein hormones that suppress pituitary FSH production. They are synthesised by follicular granulosa cells as α plus βA/βB subunits (encoded by INHA, INHBA, INHBB, respectively). Inhibin concentrations are high in follicular fluid (FF) which is also abundant in ‘free’ α subunit, presumed to be of granulosal origin, but its role(s) remains obscure. Here, we report the unexpected finding that bovine theca cells show abundant INHA expression and ‘free’ inhibin α production. Thus, theca cells may contribute significantly to the inhibin α content of FF and peripheral blood. In vitro, knockdown of thecal INHA inhibited INSL3 and CYP17A1 expression and androgen production while INSL3 knockdown reduced INHA and inhibin α secretion. These findings suggest a positive role of thecal inhibin α on androgen production. However, exogenous inhibin α did not raise androgen production. We hypothesised that inhibin α may modulate the opposing effects of BMP and inhibin on androgen production. However, this was not supported experimentally. Furthermore, neither circulating nor intrafollicular androgen concentrations differed between control and inhibin α-immunized heifers, casting further doubt on thecal inhibin α subunit having a significant role in modulating androgen production. Role(s), if any, played by thecal inhibin α remain elusive.

Trends in recombinant protein use in animal production

Recombinant technologies have made possible the production of a broad catalogue of proteins of interest, including those used for animal production. The most widely studied proteins for the animal sector are those with an important role in reproduction, feed efficiency, and health. Nowadays, mammalian cells and fungi are the preferred choice for recombinant production of hormones for reproductive purposes and fibrolytic enzymes to enhance animal performance, respectively. However, the development of low-cost products is a priority, particularly in livestock. The study of cell factories such as yeast and bacteria has notably increased in the last decades to make the new developed reproductive hormones and fibrolytic enzymes a real alternative to the marketed ones. Important efforts have also been invested to developing new recombinant strategies for prevention and therapy, including passive immunization and modulation of the immune system. This offers the possibility to reduce the use of antibiotics by controlling physiological processes and improve the efficacy of preventing infections. Thus, nowadays different recombinant fibrolytic enzymes, hormones, and therapeutic molecules with optimized properties have been successfully produced through cost-effective processes using microbial cell factories. However, despite the important achievements for reducing protein production expenses, alternative strategies to further reduce these costs are still required. In this context, it is necessary to make a giant leap towards the use of novel strategies, such as nanotechnology, that combined with recombinant technology would make recombinant molecules affordable for animal industry.

Inhibin α-subunit N terminus interacts with activin type IB receptor to disrupt activin signaling

Inhibin is a heterodimeric peptide hormone produced in the ovary that antagonizes activin signaling and FSH synthesis in the pituitary. The inhibin β-subunit interacts with the activin type II receptor (ActRII) to functionally antagonize activin. The inhibin α-subunit mature domain (N terminus) arose relatively early during the evolution of the hormone, and inhibin function is decreased by an antibody directed against the α-subunit N-terminal extension region or by deletion of the N-terminal region. We hypothesized that the α-subunit N-terminal extension region interacts with the activin type I receptor (ALK4) to antagonize activin signaling in the pituitary. Human or chicken free α-subunit inhibited activin signaling in a pituitary gonadotrope-derived cell line (LβT2) in a dose-dependent manner, whereas an N-terminal extension deletion mutant did not. An α-subunit N-terminal peptide, but not a control peptide, was able to inhibit activin A signaling and decrease activin-stimulated FSH synthesis. Biotinylated inhibin A, but not activin A, bound ALK4. Soluble ALK4-ECD bioneutralized human free α-subunit in LβT2 cells, but did not affect activin A function. Competitive binding ELISAs with N-terminal mutants and an N-terminal region peptide confirmed that this region is critical for direct interaction of the α-subunit with ALK4. These data expand our understanding of how endocrine inhibin achieves potent antagonism of local, constitutive activin action in the pituitary, through a combined mechanism of competitive binding of both ActRII and ALK4 by each subunit of the inhibin heterodimer, in conjunction with the co-receptor betaglycan, to block activin receptor-ligand binding, complex assembly, and downstream signaling.

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.

Efeito da pré-estimulação ovariana sobre características de oócitos após punção folicular em bovinos

Avaliaram-se os efeitos da pré-estimulação ovariana com FSH e da imunização ativa contra inibina suína sobre o número e classificação morfológica de oócitos recuperados por punção folicular. Catorze vacas da raça Gir, pluríparas e não-lactantes, foram distribuídas em: TI - submetidas a pré-estimulação com 250 UI de FSH (n=4), TII - submetidas a imunização ativa contra inibina suína (n=4) e TIII - não tratadas (n=6; controle). Todos os animais tiveram seus folículos com diâmetro superior a três milímetros aspirados uma vez por semana, durante 10 semanas consecutivas. O TI apresentou aumento na população folicular total (P<0,05) e no número de folículos puncionados (P<0,001), porém a taxa de recuperação foi inferior à dos tratamentos II e III (68,8% vs. 78,4% e 76,3%, respectivamente; P<0,01). O TII não afetou as principais características ovarianas, exceto pelo aumento no número de folículos de tamanho médio (P<0,01). O TI produziu maior percentual de oócitos viáveis (77,2% vs. 69,8%; P<0,05) e de oócitos de Grau I (19,8% vs. 11,6%; P<0,001) do que o TIII. Os tratamentos I e II reduziram o percentual de oócitos degenerados (16,4% e 16,8% vs. 22,3%; P<0,05). A pré-estimulação ovariana com FSH demonstrou ser a alternativa mais consistente para aumentar a qualidade dos oócitos recuperados de vacas zebuínas.

Active immunization of broiler breeder hens with a recombinant chicken inhibin fusion protein enhances egg lay

We have demonstrated that inoculation of female Coturnix with an inhibin-based immunogen (MBP-cINA521) accelerated puberty and enhanced hen-day egg production (HDEP). Herein, MBP-cINA521, a fusion protein, which consists of the bacterial maltose binding protein (MBP) and a fragment of the infinity-subunit of chicken inhibin (cINA521), was tested for its ability to enhance production performance in broiler breeders. Pullets (Arbor Acres Classic Females; n = 60 birds/treatment group) were given (subcutaneously) 0, 1, 3, or 5 mg of MBP-cINA521 in Freund's complete adjuvant at 20 wk and 4 d of age. Booster immunizations (one-half of the primary dosages) were given at 23 wk of age. The vehicle for controls (CON; no booster) and MBP-cINA521-boosted birds was Freund's incomplete adjuvant. Blood samples were obtained at the end of the trial to assess immunological response to the antigen with a titer ELISA. The onset of puberty was assessed by calculation of the average ages at first lay (FIRST) and at 50% egg production (FIFTY). Cumulative percentage HDEP was determined weekly throughout the laying period (40 wk). Egg weight (EWT) and specific gravity (SG) assessments were made periodically during the trial. Body weight gain (BWG) and mortality (MORT) data were also collected. Significant injection treatment differences (P < 0.01) in inhibin antibody titers were detected according to the following order: low dose = intermediate dose > high dose > CON. A dose of MBP-cINA521 capable of accelerating puberty and increasing overall egg lay was identified. FIRST and FIFTY responses were decreased (P < 0.05) in birds given the intermediate dose (3.0 mg) of MBP-cINA521 when compared to the CON. FIFTY responses were also lower (P < 0.05) than CON responses in those birds given the highest dose (5.0 mg) of the inhibin antigen. Cumulative HDEP was also higher (P < 0.05), beginning at 3 wk of lay and weekly thereafter (P < 0.05, for the remaining 40 wk), in birds given the intermediate immunogen dosage when compared to the CON. By Week 40, an average increase of 9.5% HDEP was realized in birds given 3.0 mg of MBP-cINA521. MORT rates were similar in the CON and in the two lowest MBP-cINA521 treatment groups but were higher (P < 0.05) in those birds given 5.0 mg of the antigen. EWT, SG, and BWG measurements were unaffected by treatment with the inhibin vaccine. In agreement with our findings in quail, immunoneutralization of inhibin enhanced production performance in breeder hens.

Effects of active immunization with inhibin alpha subunit on reproductive characteristics of turkey hens

The hypothesis for the present study is that the active immunization of female turkeys with inhibin (INH) would neutralize endogenous INH, and increase levels of circulating follicle stimulating hormone (FSH) and the number of preovulatory follicles, and subsequently enhance egg production. Two experiments were conducted with female turkeys in their first (30 wk of age) and second (62 wk of age) laying cycles. Treatment groups included control turkeys immunized with keyhole limpet hemocyanine (KLH) and experimental turkeys immunized with recombinant turkey inhibin alpha conjugated to KLH (rtINH), vasoactive intestinal peptide (VIP) conjugated to KLH or rtINH+VIP. Egg production increased (P < 0.05) in VIP and rtINH+VIP immunized birds, but not in rtINH immunized hens in comparison with a control group. A similar number of ovarian follicles, arranged in the follicular hierarchy of laying hens, was observed in all experimental groups. However, there was a larger number of nongraded yellow follicles in rtINH-immunized (62.5%) and rtINH+VIP-immunized (73.5%) groups compared with that of controls, suggesting overstimulation by FSH. Anterior pituitary FSH beta subunit, LH beta subunit, and prolactin (PRL) mRNA contents were determined by Northern blot analysis and reverse transcriptase-polymerase chain reaction (RT-PCR) in laying hens at the end of the experimental period. Hens immunized with rtINH showed increased FSH beta subunit mRNA content, but no change in the content of LH beta subunit or PRL mRNA. Hens immunized with VIP or rtINH+VIP had significant increases in both pituitary LH beta subunit and FSH beta subunit mRNA contents, accompanied by a decline in PRL mRNA abundance. The magnitude of the increase in FSH beta subunit to INH immunoneutralization was greater in first-cycle hens than in second-cycle hens. These data suggest that active immunization of female turkeys with INH neutralizes endogenous INH and increases both circulating FSH and the number of preovulatory follicles. However, no significant increase in egg production was observed in INH-immunized hens. The data confirm previous reports that VIP immunoneutralization increases egg production in turkey hens and shows for the first time that it also increases FSH beta subunit and LH beta subunit gene expression.

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.

Hormonal response of female goats to active immunization against a recombinant human inhibin alpha-subunit, and establishment of an enzyme-linked immunosorbent assay for caprine follicle-stimulating hormone

The effect of selective immunosuppression of endogenous inhibin in goats on FSH, LH, progesterone and estradiol-17beta profiles was studied during the breeding and nonbreeding seasons. Eighteen adult female Boer goats were immunized against the recombinant human inhibin alpha-subunit (hINH-alpha). With the exception of estradiol, which was determined by radio-immunoassay (RIA), all plasma hormone concentrations were determined by ELISA. The ELISA for FSH presented in this paper was established in the authors' laboratory, based on an existing RIA. Mean basal concentrations of FSH were not affected by immunosuppression of endogenous inhibin, nor was there a difference in the amplitude of the pre-ovulatory FSH surge. Immunization against inhibin appears to eliminate the slight secondary rise of FSH occurring 12-20 h after the major surge associated with ovulation. The LH profiles of the immunized goats were characterized by lower basal concentrations both before and after the pre-ovulatory LH surge which itself was reduced by 50% in immunized does. By contrast, concentrations of circulating estradiol were significantly elevated after inhibin-immunization. Progesterone profiles were not affected. Extending immunization into the anoestrous season by a booster injection of hINH-alpha, implicating oestrus induction with a progestagen and eCG, produced no discernible differences in FSH and LH profiles in comparison with nonimmunized control goats. The findings suggest that in goats, paracrine factors may play a more significant role in controlling follicular activity than a feedback mechanism acting via the pituitary.

Effect of passive immunization against inhibin on FSH secretion, folliculogenesis and ovulation rate during the follicular phase of the estrous cycle in mares

Physiological roles of inhibin in mares were investigated by means of passive immunization using an antiserum to inhibin that had been raised in a castrated goat. Eight mares were given an intravenous injection of either 100 mL (n = 4) or 200 mL (n = 4) of inhibin antiserum 4 d after a single intramuscular injection of PGF2 alpha on Day 8 after ovulation, 4 control mares were treated with 100 mL castrated goat serum in the same manner. Jugular vein blood samples were collected after treatment with the serum until 192 h post treatment. Follicular growth and ovulations were monitored by ultrasound examination at 24-h intervals. The ability of the inhibin antiserum to neutralize the bioactivity of equine inhibin was examined in vitro using a rat pituitary cell culture system. Suppression of secretion of FSH from cultured rat pituitary cells by equine follicular fluid was reversed by the addition of increasing doses of the inhibin antiserum, thereby indicating its bioactivity. Plasma levels of FSH and estradiol-17 beta were higher in mares treated with the inhibin antiserum. The ovulation rate was significantly higher in mares treated with antiserum (100 mL = 3.75 +/- 0.63; 200 mL = 4.50 +/- 0.65) than in control mares (1.25 +/- 0.25). These results demonstrate that inhibin is important in regulating FSH secretion and folliculogenesis in mares. They also show that neutralization of the bioactivity of inhibin may become a new method for the control of folliculogenesis and ovulation rate in mares.

Active immunization of Japanese quail hens with a recombinant chicken inhibin fusion protein enhances production performance

The effects of active immunization against inhibin on production performance in female Japanese quail (Coturnix coturnix japonica) were assessed in two separate trials using an MBP-cINA521 fusion protein as an immunogen. The fusion protein, MBP-cINA521, consisted of the bacterial maltose binding protein (MBP) and a truncated form of the mature alpha-subunit of chicken inhibin (cINA521). MBP-cINA1521 was constructed by: 1) excising a 521-bp PstI fragment from a chicken inhibin alpha-subunit cDNA (cINA6; gift of P. A. Johnson), 2) cloning this fragment, which encodes all but the first 11 amino acid residues of the mature alpha-subunit, into the pMal-c2 vector of the MBP fusion expression system, and 3) expressing the fusion protein (MBP-cINA521) from the Escherichia coli and purifying it using affinity chromatography. In each trial, quail were randomly and equally assigned to one of two injection treatments as follows: 1) MBP-cINA521 in Freund's adjuvant, or 2) Freund's adjuvant (vehicular controls; CON). All immunizations were given subcutaneously and Freund's complete and incomplete adjuvant were used for primary and booster injections, respectively. In Trial 1, birds were given a primary challenge of 0.2 mg MBP-cINA521 per bird at 25 d of age, followed by booster immunizations (0.1 mg MBP-cINA521 per bird) at 33, 40, 47, 54 and 61 d of age and every 35 d thereafter. The CON birds received vehicular immunizations at the same time intervals. In Trial 2, birds treated with MBP-cINA521 received a primary challenge of 0.2 mg MBP-cINA521 per bird at 26 d of age, followed by booster immunizations (0.1 mg MBP-cINA521 per bird) using the same schedule as that used in Trial 1, with the exception that no boosters were given after 61 d of age. The CON birds received vehicular immunizations at the same time intervals. Collection of production performance data was initiated coincident with the laying of the first egg in each trial (i.e., beginning at 41 and 44 d of age for Trials 1 and 2, respectively) and continued for 30 1-wk periods of lay. Combined data from Trials 1 and 2 indicated that the mean +/- SE age at first egg lay was markedly decreased (P < 0.005) in MBP-cINA521-treated quail (53.4 +/- 0.9 d of age) when compared to the CON (57.6 +/- 1.3 d of age). Likewise, the mean +/- SE age at 50% egg production was reduced (P < 0.03) in quail immunized against inhibin (65.4 +/- 2.1 d of age) when compared to the CON (77.6 +/- 4.7 d of age). Total hen-day egg production was also higher (P < 0.05, Trial 1; P < 0.01, Trial 2) in MBP-cINA521-treated quail (88.7 +/- 1.4%, Trial 1; 90.1 +/- 1.2%, Trial 2) than in the CON birds (81.9 +/- 2.9%, Trial 1; 73.6 +/- 6.5%, Trial 2). Collectively, these findings provide evidence that inhibin immunoneutralization accelerated puberty and enhanced hen-day egg production during a 30-wk period of egg lay in Japanese quail.

Production of a genetically engineered inhibin vaccine

The goal of this research was to synthesize a chimeric ovalbumin/inhibin antigen using recombinant techniques. Antigenic epitopes of the translated product from an ovalbumin cDNA were mapped using computer modeling techniques. The corresponding nucleotide sequences of ovalbumin epitopes were examined for unique restriction sites to allow insertion of a synthetic bovine inhibin alpha gene fragment which encoded the first 26 amino acids. A plasmid (pETOI-8) was synthesized which contained the chimeric ovalbumin/inhibin alpha 1-26 gene. A 46 kDa recombinant protein (ovalin) was produced from BL21 (DE3) Escherichia coli cells containing pETOI-8 that was identified with anti-ovalbumin and anti-inhibin alpha 1-26 antisera. Rabbits were immunized subcutaneously in four sites along the back against ovalbumin (n = 3), crude ovalin (n = 3), or gel-purified ovalin (n = 3) at week 0, 4, 7, and 18. Primary and booster immunizations contained ca 300 micrograms of antigen emulsified in complete Freund's adjuvant and incomplete Freund's adjuvant, respectively. Blood samples collected at week 0, 6, 8, and 19 were evaluated for their ability to bind ovalbumin, 32 kDa bovine inhibin and bovine inhibin alpha 1-26 using ELISA. Mean anti-ovalbumin titers at week 19 were 1:100000 in rabbits immunized against ovalbumin or crude ovalin, and 1:23333 in rabbits immunized against gel-purified ovalin. Anti-inhibin and anti-inhibin alpha 1-26 titers were nonexistent in antisera from pre-immunized rabbits and rabbits immunized against ovalbumin. Mean anti-inhibin titers at week 19 were 1:833 and 1:10000 in rabbits immunized against crude ovalin or gel-purified ovalin, respectively. Mean anti-inhibin alpha 1-26 titers at week 19 were 1:3333 and 1:6666 in rabbits immunized against crude or gel-purified ovalin, respectively. We conclude that genetic engineering of inhibin alpha 1-26 into the antigenic epitopes of ovalbumin provides potential for the development of an anti-inhibin vaccine.

Immunoregulation of mammalian fertility

Fertility management is a global issue of agricultural, medical, economic, and social consequence. Although many methods have been devised to both inhibit and assist reproduction, more acceptable alternatives are needed. Regulation by immune intervention is a promising technology as applied to livestock, pets, wildlife, and human beings. Outcome is dictated by site within the reproductive axis that is targeted. Fertility is suppressed by immunization against gonadotropin-releasing hormone, gonadotropins, prostaglandin F2 alpha, oxytocin, gonadotropin receptors, and gamete/embryonic antigens. It also is possible to lyse gonadal cells with ligand-antibody hybrid molecules. Ovulation rates are enhanced by vaccination with inhibin. Antibodies to sex steroid hormones have yielded mixed results. Perhaps recombinant viral vectors can be used to deliver reproductive immunogens. A new and simple technique to generate sustained autoimmune reactions to hormones and cellular antigens entails direct gene transfer into somatic cells. Evolving advances in reproductive immunology and biotechnology should furnish us with novel nonsurgical contraceptives and profertility agents that can be efficiently and safely implemented.

Interrelationships of hormonal and ovarian responses in superovulated heifers pretreated with FSH-P at the beginning of the estrous cycle

The objective of this study was to determine the relationships between follicle stimulating hormone, (FSH), estradiol (E(2)), and progesterone (P(4)) concentrations in peripheral blood samples and the follicular dynamics prior to and during superovulation in heifers pretreated with FSH-P (10 mg, i.m.) (FSH-P-primed; n=9) or not (saline-primed; n=9) on Day 3 (Day 0 = estrus) of the estrous cycle. On Day 10, all heifers were superovulated with FSH-P (27.7 mg i.m.) in declining dosages over 5 days. Prior to and during superovulation, blood samples were collected one to five times daily, and the follicular dynamics were monitored daily by ultrasonography. Prior to superovulation, profiles of P(4) and E(2) did not differ (P>1) between the saline- and FSH-P-primed heifers. The FSH concentrations in saline-primed heifers decreased from 0.43 +/- 0.05 ng/ml to 0.30 +/- 0.04 ng/ml between Days 3 and 7 and then increased progressively to 0.59 +/- 0.04 ng/ml on Day 10. In contrast (P<0.002), FSH concentrations in the FSH-P-primed heifers remained constant between Days 3 and 10 and averaged 0.41 +/- 0.03 ng/ml. Higher increases in E(2) during superovulation (maximum values, 100 vs 46 pg/ml) and in P(4) after superovulation (maximum values, 39 vs 22 ng/ml) in the saline-than in the FSH-P-primed heifers reflected the greater increase in the number of follicles (>10 mm) and in the number of corpora lutea (CL) in the saline-primed heifers. Prior to the preovulatory luteinizing hormone (LH) peak during superovulation, there was a parallel (P>0.1) decrease in FSH concentrations in the saline- and FSH-P-primed groups. Within heifers partial correlations indicated that E(2) was correlated positively with the number of follicles (>/= 7 mm) and the size of the largest follicle during superovulation (r=0.54 to 0.81; P<0.01). Negative correlations were detected (P<0.01) between FSH and the number of follicles >/=7 mm prior to (r=-0.26) and during superovulation (r=-0.37). The results cofirm earlier reports indicating that priming with FSH-P decreases the superovulatory response in cattle. Interrelationships of hormonal and ovarian responses support the concept that the presence of large dominant follicles prior to superovulation limits the superovulatory response.

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.

Effect of immunizing prepuberal lambs of low and high ovulation rate genotypes with inhibin partially purified from bovine follicular fluid

Active immunization of prepuberal lambs with a partially purified inhibin preparation, isolated from bovine follicular fluid, increased the ovulation rate. In ewe lambs of a low fecundity breed (Suffolk x Galway), the ovulation rate rose from 1.15 to 1.95 (P<0.05) compared with that of the controls. An ovulation rate of 3.38 was recorded for immunized ewe lambs of a high fecundity breed (Finn x Dorset Horn), while the rate for mature ewes from the same flock was 2.29. Immunization did not affect the time of onset of puberty or estrous cycle length. Following immunization, antibodies were produced that bound to a pure preparation of 68kDa bovine inhibin. This report demonstrates the production of antibody to a 68kDa preparation of inhibin following active immunization of sheep using a partially purified preparation. It was concluded that the increased ovulation rate was due to the production of antibodies to inhibin, which may have reduced its negative feedback effect of FSH secretion.