Effect of long-term immunization against inhibin on sperm output in bulls

GALLO: An R package for genomic annotation and integration of multiple data sources in livestock for positional candidate loci

BACKGROUND

The development of high-throughput sequencing and genotyping methodologies has enabled the identification of thousands of genomic regions associated with several complex traits. The integration of multiple sources of biological information is a crucial step required to better understand patterns regulating the development of these traits.

FINDINGS

Genomic Annotation in Livestock for positional candidate LOci (GALLO) is an R package developed for the accurate annotation of genes and quantitative trait loci (QTLs) located in regions identified in common genomic analyses performed in livestock, such as genome-wide association studies and transcriptomics using RNA sequencing. Moreover, GALLO allows the graphical visualization of gene and QTL annotation results, data comparison among different grouping factors (e.g., methods, breeds, tissues, statistical models, studies), and QTL enrichment in different livestock species such as cattle, pigs, sheep, and chickens.

CONCLUSIONS

Consequently, GALLO is a useful package for annotation, identification of hidden patterns across datasets, and data mining previously reported associations, as well as the efficient examination of the genetic architecture of complex traits in livestock.

Passive immunization against inhibin increases testicular blood flow in male goats

The present study investigated whether or not passive immunization against inhibin modulates testicular blood flow in goats. Male Shiba goats were injected with either 10 ml of inhibin antiserum (INH group; n = 5) or 10 ml of normal castrated goat serum (NGS group; n = 4). Concentrations of FSH, LH, testosterone (T), and estradiol (E2) in the plasma were measured by radioimmunoassay. Blood flow within the supratesticular (STA) and marginal testicular arteries (MTA) were measured by color pulsed-Doppler ultrasonography, and Doppler indices (resistive index; RI and pulsatility index; PI) were recorded. Results revealed significant increases in concentrations of FSH and E2 in the INH group compared to those in the NGS group (P < 0.05). Animals in the INH group had greater (P < 0.05) FSH concentrations than those in the NGS group in the period between 60 h and 144 h after treatment than at any other time. Estradiol concentrations were greater (P < 0.05) in the INH group than in the NGS group at 6 h (12.15 ± 2.09 pg/ml vs 5.49 ± 1.17 pg/mL), 12 h (8.27 ± 1.29 pg/mL vs 3.05 ± 0.38 pg/mL), and 36 h (9.35 ± 1.31 pg/mL vs 5.09 ± 0.46 pg/mL) after treatment than at any other time. Concentrations of LH and T did not significantly change between the two groups. Goats in the INH group had lesser (P < 0.05) RI of the STA than those in the NGS group and RI values were lesser at 24 h (0.37 ± 0.031 vs 0.49 ± 0.004) and 120 h (0.38 ± 0.028 vs 0.55 ± 0.048) after treatment than at any other time. Furthermore, values of RI and PI of the MTA were significantly lesser (P < 0.05) in the INH group compared to those in the control group at 48 h (RI of MTA: 0.21 ± 0.014 vs 0.37 ± 0.039; PI of MTA: 0.24 ± 0.016 vs 0.46 ± 0.058) after treatment than at any other time. In conclusion, passive immunization against inhibin has a stimulatory effect on testicular blood flow in goats by inducing decreases in the RI values of the STA and MTA.

The effect of active immunization against vasoactive intestinal peptide (VIP) and inhibin on reproductive performance of aging White Leghorn roosters

Decreasing fertility in aging domestic roosters is a well-known phenomenon. Aging is manifested by a decrease in plasma testosterone level, testis function, and spermatogenesis, resulting in a low level of fertility. The roles of vasoactive intestinal peptide (VIP) and testicular inhibin in this aging process are not clear. The effects of active immunization against VIP, inhibin, or the combination of both hormones on the reproduction of aging White Leghorn (WL) roosters were assayed. In experiment 1a, 60 White Leghorn roosters (67 wk of age) were divided into 4 groups (n = 15/group). The first group was actively immunized against VIP, the second against inhibin, the third against VIP and inhibin, and the fourth served as a control. Active immunization against VIP decreased semen quality parameters, plasma steroid levels, and gene expression of gonadotropin-releasing hormone-I (GnRH-I), follicle-stimulating hormone (FSH), luteinizing hormone (LH), LH receptor, VIP, and prolactin (Prl). Immunization against inhibin increased some of the semen quality parameters and FSH mRNA gene expression but decreased inhibin gene expression. In experiment 1b, at 94 wk of age, we took the actively immunized against VIP group and the control group and divided them into 2 subgroups (n = 7 or 8): the first group was injected with 1 mg of ovine Prl (oPrl) daily for 7 d, and the second group served as a control. Administration of oPrl to previously VIP-immunized birds significantly elevated semen quality parameters. We suggest that VIP, Prl, and inhibin have an important effect on the reproductive axis in aging roosters. Active immunization against VIP-depressed reproductive activity and Prl administration restored their reproduction, indicating that both VIP and Prl are essential for reproduction in aging roosters. Immunization against inhibin improved FSH mRNA gene expression, suggesting a negative role of inhibin on FSH secretion in aging roosters. Not all semen quality parameters increased significantly after immunization against inhibin, even though FSH mRNA gene expression increased, suggesting interference in testicular function in aging roosters.

Action mechanism of inhibin α-subunit on the development of Sertoli cells and first wave of spermatogenesis in mice

Inhibin is an important marker of Sertoli cell (SC) activity in animals with impaired spermatogenesis. However, the precise relationship between inhibin and SC activity is unknown. To investigate this relationship, we partially silenced both the transcription and translation of the gene for the α-subunit of inhibin, Inha, using recombinant pshRNA vectors developed with RNAi-Ready pSIREN-RetroQ-ZsGreen Vector (Clontech Laboratories, Mountain View, Calif). We found that Inha silencing suppresses the cell-cycle regulators Cyclin D1 and Cyclin E and up-regulates the cell-cycle inhibitor P21 (as detected by Western blot analysis), thereby increasing the number of SCs in the G1 phase of the cell cycle and decreasing the amount in the S-phase of the cell cycle (as detected by flow cytometry). Inha silencing also suppressed Pdgfa, Igf1, and Kitl mRNA levels and up-regulated Tgfbrs, Inhba, Inhbb, Cyp11a1, Dhh, and Tjp1 mRNA levels (as indicated by real-time polymerase chain reaction [PCR] analysis). These findings indicate that Inha has the potential to influence the availability of the ligand inhibin and its antagonist activin in the SC in an autocrine manner and inhibit the progression of SC from G1 to S. It may also participate in the development of the blood–testis barrier, Leydig cells, and spermatogenesis through its effect on Dhh, Tjp1, Kitl, and Pdgfa. Real-time PCR and Western blot analyses of Inha, Inhba, and Inhbb mRNA and Inha levels over time show that Inha plays an important role in the formation of round spermatid during the first wave of spermatogenesis in mice.

The effect of lead intoxication on endocrine functions

Studies on the effects of lead on the endocrine system are mainly based on occupationally lead-exposed workers and experimental animal models. Although evidence is conflicting, it has been reported that accumulation of lead affects the majority of the endocrine glands. In particular, it appears to have an effect on the hypothalamic-pituitary axis causing blunted TSH, GH, and FSH/LH responses to TRH, GHRH, and GnRH stimulation, respectively. Suppressed GH release has been reported, probably caused by reduced synthesis of GHRH, inhibition of GHRH release or reduced somatotrope responsiveness. Higher levels of PRL in lead intoxication have been reported. In short-term lead-exposed individuals, high LH and FSH levels are usually associated to normal testosterone concentrations, whereas in long-term exposed individuals' low testosterone levels do not induce high LH and FSH concentrations. These findings suggest that lead initially causes some subclinical testicular damage, followed by hypothalamic or pituitary disturbance when longer periods of exposure take place. Similarly, lead accumulates in granulosa cells of the ovary, causing delays in growth and pubertal development and reduced fertility in females. In the parenchyma of adrenals histological and cytological changes are demonstrated, causing changes in plasma basal and stress-mediated corticosterone concentrations and reduced cytosolic and nuclear glucocorticoid receptor binding. Thyroid hormone kinetics are also affected. Central defect of the thyroid axis or an alteration in T4 metabolism or binding to proteins may be involved in derangements in thyroid hormone action. Lead toxicity involves alterations on calcitropic hormones' homeostasis, which increase the risk of skeletal disorders.

Endocrine status and development of porcine testicular tissues in host mice

Clarification of the endocrine status of host mice provides us with basic knowledge with which we can manipulate the growth and function of xenografted testicular tissues. We investigated the hormonal profiles of castrated mice grafted with porcine immature testicular tissues from 30 to 210 or more days after grafting (day 0=castration and grafting). The serum follicle stimulating hormone (FSH) concentrations of the host mice declined (P<0.05) from day 60 compared with those of the castrated, ungrafted mice. The serum inhibin and testosterone levels were higher (P<0.05) than those in the castrated, ungrafted mice from days 30 and 90 days, respectively. The inhibin levels further increased (P<0.05) from day 90, during which time the levels were higher (P<0.05) than those in the intact male mice. In the grafts, formation of lumens occurred in the seminiferous cords on day 90 and spermatozoa appeared in the lumens from day 120. However, spermatogenesis in the grafts did not reach the qualitatively normal levels observed in adult boars. The intensity of the immune reaction to inhibin alpha subunits in the Sertoli cells of the grafts decreased with differentiation of the seminiferous tubules. The present findings indicate that a feedback loop was established between the mouse hypothalamo-pituitary axis and the grafted porcine tissues from 60 days post-grafting. The results also indicate that the serum inhibin levels in the host mice remained high even after the appearance of lumens in the seminiferous tubules of the grafted tissues; this is strikingly different to the situation in normal male animals, in which the serum inhibin levels decline at around the time of tubular differentiation. The lack of efferent ducts in the tubules of the grafted tissues probably caused the accumulation of inhibin to be released into the lumens, resulting in high concentrations of circulating inhibin. These high levels of inhibin may directly affect spermatogenic activity and suppress FSH secretion.

Effects of immunization against two inhibin antigens on daily sperm production and hormone concentrations in ram lambs1

The gonadal hormone inhibin regulates daily sperm production (DSP) indirectly through negative feedback control of FSH secretion and may also affect DSP via direct actions within the testis. Studies attempting to increase DSP through the immunization against inhibin have yielded equivocal results. The current study compared 2 inhibin antigens for effects on DSP and hormone secretion. Hampshire ram lambs (BW = 42 +/- 2 kg; age = 113 +/- 3 d) were assigned randomly to 3 groups: 1) control (n = 4); 2) alpha-peptide conjugate (PTC, n = 6); and 3) alpha-subunit (SUB, n = 6). Antigen PTC consisted of an alpha-inhibin, N-terminal, 25-amino acid peptide conjugated to ovalbumin. Antigen SUB was the complete inhibin alpha-subunit. Lambs were immunized on d 0 (June 19, 2006), 18, 38, and 63. Body weight was recorded on immunization days and scrotal circumference on d 63. Blood samples were collected on d 0, 7, 14, 18, 28, 35, 38, 49, 56, 63, and 70. Rams were slaughtered on d 71. Testes were weighed, and parenchyma was obtained for DSP determination. Plasma alpha-inhibin antibody titer and LH, FSH, and testosterone concentrations were measured. alpha-Inhibin antibody titer was first detectable on d 14 in both PTC- and SUB-immunized ram lambs and generally increased thereafter. Mean DSP per gram of testis (DSP/g) was increased (P < 0.01) 26% in PTC- and SUB-immunized ram lambs over that in control ram lambs. Total DSP per ram lamb and testes weight did not differ among the 3 treatment groups. Variation in DSP per ram lamb and testes weight were greater (P = 0.05) in PTC- and SUB-immunized ram lambs than in control ram lambs. Plasma FSH concentrations were similar in PTC- and SUB-immunized ram lambs. Immunization against either alpha-inhibin antigen did not alter LH, testosterone, BW, or scrotal circumference. Findings indicate that 1) the 2 alpha-inhibin antigens increase DSP/g to similar extents; 2) alpha-inhibin antibody may act at least in part through an intratesticular mechanism because DSP/g was increased in some animals without concomitant increases in FSH; and 3) immunization against alpha-inhibin may affect testes weight by actions independent of those that regulate DSP/g.

Production of inhibin A and inhibin B in boars: changes in testicular and circulating levels of dimeric inhibins and characterization of inhibin forms during testis growth

We investigated the production of inhibin in boars from the infantile to pubertal periods by: (1) measurement of testicular and circulating levels of inhibin, (2) characterization of inhibin forms and (3) localization of inhibin alpha subunits in the testis. Total inhibin levels in the testis increased until 8 weeks of age but then declined to much lower values at 15 weeks. Testicular inhibin A and inhibin B were high until 8 weeks. Circulating levels of total inhibin and inhibin A were also high until 8 weeks, then declined from 10 weeks; inhibin B was not detected, because of low sensitivity of the inhibin B assay. Analyses of inhibin A and inhibin B levels in the eluted fractions obtained from testes after immunoaffinity chromatography and SDS-PAGE showed the presence of a peak of approximately 45 kDa until 10 weeks of age. As the boars aged, the levels of inhibin A and inhibin B increased in the molecular weight region of 29-31 kDa. The fractions corresponding to 29 and 30 kDa suppressed FSH release from rat pituitary cells, but the 45 kDa fraction had no FSH-suppressing activity. Total amounts of inhibin A isolated from the SDS gels were similar to those of inhibin B until 10 weeks of age, but were three times higher than those of inhibin B between 15 and 25 weeks. Further fractionation by reverse phase high-performance liquid chromatography revealed that the 29-31 kDa immunoreactive material was composed of mature forms of inhibin A and inhibin B, in addition to a 26 kDa alpha monomer. Immunohistochemistry indicated that positive immunostaining for the alpha subunits was observed in Sertoli cells from the infantile to pubertal periods. Elongated spermatids also showed positive signals at age 25 weeks. These results clearly indicated that: (1) the boar testis has the ability to produce inhibin A and inhibin B during the infantile period but inhibin A is the predominant form towards puberty and (2) the molecular weight forms of inhibin and the sites of production of inhibin change with testicular development.

Changes in the testis seminiferous tubules and interstitium in prepubertal bull calves immunised against inhibin at the time of gonadotropin administration

The aim of the present study was to evaluate the effects of gonadotropin administration at initiation of inhibin passive immunisation in Jersey bull calves (age 27 � 5 days) on testicular morphology and development. Primary treatments consisted of control (keyhole limpet haemocyanin, KLH; n = 9) or immunisation against inhibin (INH; n = 9). Subsets of calves were randomly assigned within primary treatments (TRT) to receive saline ( n = 3 per TRT), follicle-stimulating hormone (FSH; n = 3 per TRT) or gonadotrophin-releasing hormone (GnRH, n = 3 per TRT). The right testis was removed (age 118 � 5 days) to determine volumes of testicular components and cell numbers per testis using stereology. Data were analysed using the MIXED procedure of the SAS program. Antibody titres against inhibin were increased in INH bulls compared with KLH bulls (P < 0.05). In addition, a significant immunisation � hormone treatment interaction was noted for the number of germ cells. Administration of FSH at the time of initial immunisation against inhibin significantly increased the number of germ cells (92.2 � 9 � 106 cells) compared with INH+saline bulls (54.9 � 10 � 106 cells), with INH+GnRH bulls having an intermediate number of cells (64.5 � 9 � 106 cells; P < 0.05). These results suggest that gonadotropin administration at the time of inhibin immunisation increases the number of germ cells in the testis.

Mechanisms of Disease: late-onset hypogonadism

Late-onset hypogonadism (formerly called the andropause) is a clinical and biochemical syndrome associated with advancing age, which is characterized by typical signs and symptoms and a deficiency in serum testosterone levels. Age-related hypoandrogenism in the male is a result of the interaction of hypothalamopituitary and testicular factors. The hypothalamic pulsatile secretion of gonadotropin-releasing hormone is blunted, due to increased hypothalamic sensitivity to inhibition by steroids, but the responsiveness of the pituitary gonadotrophs seems to be intact. In addition, testicular volume as well as Leydig cell mass and reserve function are diminished. Taken together, these mechanisms result in reduced testosterone secretion and the loss of nycthemeral variability.

Active immunization of broiler breeder cockerels against chicken inhibin accelerates puberty and prevents age-induced testicular involution

Injection of quail and breeder hens with a recombinant protein antigen (MBP-cINA521)--a fusion of the bacterical maltose-binding protein (MBP) and a fragment of the alpha-subunit of chicken inhibin (cINA521)--accelerates puberty and enhances lay. Herein, the effects of this immunogen on reproductive responses in broiler breeder males were assessed. Cockerels were subcutaneously injected with 0 (vehicular controls), 1, 3, or 5 mg of MBP-cINA521 at 13 wk of age and with one-half of these dosages (boosters) at 18 wk. Bird subsamples were weighed, blood sampled, and killed at 24, 28, and 39 wk of age to assess age and vaccination effects on BW, testes weight (TWT), TWT relative to BW (RTWT), TWT > or = 20 g (TWT20; theoretical threshold TWT for maximum fertility), and plasma testosterone. Breeder males are sexually developing, reach peak sexual activity, and show age-related reproductive decline at these ages. Because vaccine gonadal effects at 24 wk appeared to be dramatic, the size of the left testis was also scored to see if size differences could be detected by mere visual inspection. Male fighting increasingly reduced sample sizes beyond 24 wk. Because mortality was unrelated to the treatments and to insure meaningful statistical comparisons, MBP-cINA521 data were pooled. Body weight (P < 0.04), testis score (P < 0.02), TWT (P < 0.03), RTWT (P = 0.06), and plasma testosterone (P = 0.08) were elevated in immunogen-treated males at 24 wk of age, and more (P < 0.05) MBP-cINA521-treated birds than controls achieved a TWT20 at this time. These variables did not differ by treatment at 28 wk. However, by 39 wk, treatment effects reemerged as follows: TWT (P < 0.04), RTWT (P = 0.06), and TWT20 (P < 0.01) were increased in vaccinated males who also showed nearly 3-fold higher levels of plasma testosterone. We conclude that immunoneutralization of inhibin accelerates puberty and retards age-related sexual senescence that typically occurs in broiler breeder males.

Effect of active immunization against inhibin on hormonal concentrations and semen characteristics in Shiba bucks

Active immunization against inhibin increased ovulation rate in females; in males, the effects of active immunization against inhibin on hormonal concentrations and sperm production need more investigation. To test the hypothesis that active immunization against inhibin increases FSH secretion and sperm output, the present study was undertaken to determine the effects of active immunization against inhibin on hormonal profile and sperm production in Shiba bucks. The bucks were actively immunized against inhibin alpha-subunit (immunized group, n=6) or Freund adjuvant (control group, n=5) four times, at 5-weeks intervals. Blood samples were collected twice-weekly and two successive ejaculates of semen were collected (with an artificial vagina) once-weekly. Plasma concentrations of FSH, LH and testosterone were measured by radioimmunoassay (RIA) and sperm motility characteristics were measured by computer-assisted sperm analysis (CASA). All inhibin-immunized bucks produced antibodies against inhibin. Relative to control bucks, in immunized bucks there were significant increases in plasma FSH concentrations and in sperm concentrations from 5 to 9 weeks and from 8 to 11 weeks, respectively, after primary immunization. However, plasma concentrations of LH and testosterone, semen volume, percentage of motile spermatozoa and motility parameters (straight-line velocity, curvilinear velocity and linearity index) were similar in both groups. In conclusion, active immunization against inhibin alpha-subunit increased FSH secretions and enhanced sperm production in bucks, whereas LH and testosterone concentrations, semen volume and sperm motility parameters were unaffected. Active immunization against inhibin could be used to improve fertility in Shiba bucks.

Changes in Circulating and Testicular Levels of Inhibin A and B During Postnatal Development in Bulls

We investigated testicular and circulating levels of dimeric inhibins in Holstein bulls from the infantile to postpubertal periods (5 to 50 weeks of age) and examined the relationship between the profiles of circulating dimeric inhibins and FSH. Concentrations of total inhibin and inhibin B in the testis were highest at 4 to 5 weeks of age but decreased gradually as the bulls aged. Testicular inhibin A levels showed a gradual decline to a nadir at 15 to 26 weeks of age, but by 39 weeks, they were high again. The contents of total inhibin, inhibin A, and inhibin B per testis generally increased with age. Fractionation of testicular homogenates obtained from 15-week-old bulls by a combination of immunoaffinity chromatography and SDS-PAGE confirmed the presence of two major molecular weight forms (32 and 45 kDa) of dimeric inhibins in the testes. Circulating levels of total inhibin and inhibin A showed a significant increase in bulls at around 10 to 14 weeks of age compared to the levels between 5 and 7 weeks of age but decreased thereafter. However, immunoreactivity for inhibin B was not detected in the peripheral circulation, probably because of low sensitivity of the inhibin B assays. The concentrations of plasma FSH were high at 5 weeks of age but declined to lower levels between 11 and 40 weeks, and then increased from 41 weeks onward. There was no significant correlation between the plasma levels of FSH and inhibin A or total inhibin. The results clearly indicate that the bull testis produces inhibin A and B and secretes at least inhibin A into the circulation during postnatal development. However, the profile of circulating FSH in bulls shows no reciprocal relationship with the inhibin A or total inhibin profile during the postnatal period.

Is inhibin B involved in the toxic effect of lead on male reproduction?

Human studies indicate exposure to lead is associated with decreased sperm quality with modest, if any, effects on conventional reproductive endocrine profile. Inhibin B is a marker of Sertoli cell function and spermatogenesis. The present study evaluates possible effects of lead exposure on serum levels of inhibin B in a group of lead workers as compared with a non-exposed group of hospital personnel. The study population included 68 healthy Belgian workers from a lead smelter (Hoboken, Belgium) and for comparison a control group of 91 hospital personnel (University Hospital Ghent, Belgium). Semen analysis and measurement of current blood lead levels and serum levels of inhibin B, follicle stimulating hormone (FSH) and estradiol (E2). Lead workers had significantly lower sperm concentration (35 vs. 51 million/mL) and higher serum inhibin B (259 vs. 177 pg/mL) as well as lead blood levels 30.9 vs. 3.4 mug/dL) compared with the hospital personnel (all p < 0.05). Serum FSH and E2 levels were similar in both groups. Overall, inhibin B levels correlated significantly positively with blood lead levels and sperm concentration while it was negatively correlated with serum FSH. In multiple regression analysis of data from all participants, blood lead and serum FSH (p < 0.0001 for both) followed by sperm count (p = 0.007) were selected as the only independent variables for inhibin B with an R-adjusted coefficient of determination of 0.3714. The results of the present study suggest that the exposure of the cells of Sertoli to excessive amounts of lead results in inappropriate inhibin B overproduction that may be involved in the impairment of spermatogenesis.

Combined conventional/antioxidant "Astaxanthin" treatment for male infertility: a double blind, randomized trial

AIM

To evaluate the treatment of male infertility with a strong natural antioxidant, in addition to conventional treatment.

METHODS

Using a double blind, randomized trial design, 30 men with infertility of > or =2 months and female partners with no demonstrable cause of infertility received conventional treatment according to the guidelines of the World Health Organization (WHO), and either a strong antioxidant Astaxanthin 16 mg/day (AstaCarox, AstaReal AB, Gustavsberg, Sweden) or placebo for 3 months. The effects of treatment on semen parameters, reactive oxygen species (ROS), zona-free hamster oocyte test, serum hormones including testosterone, luteinizing hormone (LH), follicle stimulating hormone (FSH) and Inhibin B, and spontaneous or intrauterine insemination (IUI)-induced pregnancies were evaluated.

RESULTS

ROS and Inhibin B decreased significantly and sperm linear velocity increased in the Astaxanthin group (n = 11), but not in the placebo group (n = 19). The results of the zona-free hamster oocyte test tended to improve in the Astaxanthin group in contrast with the placebo group, though not reaching statistical significance. The total and per cycle pregnancy rates among the placebo cases (10.5 % and 3.6 %) were lower compared with 54.5 % and 23.1 % respectively in the Astaxanthin group (P = 0.028; P = 0.036).

CONCLUSION

Although the present study suggests a positive effect of Astaxanthin on sperm parameters and fertility, the results need to be confirmed in a larger trial before recommending Astaxanthin for the complementary treatment of infertile men.

Using gonadotropin-releasing hormone (GnRH) and GnRH analogs to modulate testis function and enhance the productivity of domestic animals

Gonadotropin releasing hormone (GnRH) controls the activity of the gonadotrope cells of the pituitary gland and, as a consequence, is a critical component of the endocrine cascade that determines the growth, development, and functional activity of testicular tissue. The use of GnRH and GnRH analogs is common in domestic animal production systems. Although GnRH and GnRH analogs are most commonly used to control the fertility and reproductive events in female animals, GnRH agonists and antagonists are increasingly used to modulate the fertility, behavior, and productivity of male animals as well. This review will focus on recent advances in this use of GnRH agonists and antagonists.

Numbers of antral follicles during follicular waves in cattle: evidence for high variation among animals, very high repeatability in individuals, and an inverse association with serum follicle-stimulating hormone concentrations

The extent, causes, and physiological significance of the variation in number of follicles growing during ovarian follicular waves in human beings and cattle are unknown. Therefore, the present study examined the variability and repeatability in numbers of follicles 3 mm or greater in diameter during the follicular waves in bovine estrous cycles, and we determined if the variation in number of follicles during waves was associated with alterations in secretion of FSH, estradiol, inhibin, and insulin-like growth factor I (IGF-I). Dairy cattle were subjected to twice-daily ultrasound analysis to count total number of antral follicles 3 mm or greater in diameter throughout 138 different follicular waves. In another study, blood samples were taken at frequent intervals from cows that consistently had low or very high numbers of follicles during waves and were subjected to immunoassays. Results indicate the following: First, despite an approximately sevenfold variation in number of follicles during waves among animals and marked differences in age, stage of lactation, and season of the year, a very highly repeatable (0.95) number of follicles 3 mm or greater in diameter is maintained during the ovulatory and nonovulatory follicular waves of individuals. Second, variation in number of follicles 3 mm or greater in diameter during waves and the inverse association of number of follicles during waves with FSH are not directly explained by alterations in the patterns of secretion of estradiol, inhibin, or IGF-I. Third, ovarian ultrasound analysis can be used reliably by investigators to identify cattle that consistently have low or high numbers of follicles during waves, thus providing a novel experimental model to determine the causes and physiological significance of the high variation in antral follicle number during follicular waves among single-ovulating species, such as cattle or humans.

Activins, inhibins and follistatins in the large domestic species

The activins and inhibins are members of the transforming growth factor-beta (TGF-beta) superfamily and, along with follistatin, a high affinity binding protein of activin, form a group of interrelated factors originally isolated for their role in regulating the release of follicle-stimulating hormone (FSH). Knowledge of their function, particularly that of activin, has expanded since being originally isolated, such that they are now regarded as important paracrine regulators in many cellular systems. This review summarizes the biology of these proteins as has been established in the large domestic animals. While the majority of data relate to the pituitary, ovary, uterus/placenta and testis, consideration is also given to emerging roles in inflammatory processes and in non-reproductive tissues or systems.

Effects of treatment with LH or FSH from 4 to 8 weeks of age on the attainment of puberty in bull calves

A transient increase in gonadotropin secretion between 6 and 20 weeks of age is critical for the onset of puberty in bull calves. To try and hasten the onset of puberty, bull calves were treated (s.c.) with 3 mg of bLH (n = 6) or 4 mg of bFSH (n = 6) once every 2 days, from 4 to 8 weeks after birth; control calves received saline (n = 6). At 4 and 8 weeks of age, mean LH concentrations were higher (P < 0.05) in bLH-treated (2.3 +/- 0.04 ng/ml and 1.20 +/- 0.04 ng/ml) as compared to control calves (0.50 +/- 0.1 ng/ml and 0.70 +/- 0.10 ng/ml). Mean serum FSH concentrations at 4 and 8 weeks of age, were higher (P < 0.05) in bFSH-treated (1.60 +/- 0.20 ng/ml and 1.10 +/- 0.2 ng/ml) as compared to control calves (0.38 +/- 0.07 ng/ml and 0.35 +/- 0.07 ng/ml). The age at which scrotal circumference (SC) first reached > or = 28 cm, occurred earlier (P < 0.05) in bFSH-treated calves as compared to saline-treated calves (39.3 +/- 1.3 and 44.8 +/- 1.3 weeks of age, respectively). Based on testicular histology at 56 weeks of age, treatment with bFSH resulted in greater (P < 0.05) numbers of Sertoli cells (5 +/- 0.2, 6 +/- 0.3 and 5 +/- 0.3 in bLH-, bFSH- and saline-treated calves, respectively); elongated spermatids (42 +/- 2, 57 +/- 8 and 38 +/- 5 in bLH-, bFSH- and saline-treated calves, respectively) and spermatocytes (31 +/- 3, 38 +/- 3 and 29 +/- 2 in bLH-, bFSH- and saline-treated calves, respectively) per seminiferous tubule. We concluded that treatment of bull calves with bFSH from 4 to 8 weeks of age increased testicular growth (SC); hastened onset of puberty (SC > or = 28 cm); and enhanced spermatogenesis.

Molecular weight forms of inhibin a and inhibin B in the bovine testis change with age

To investigate alterations in the molecular weight forms of inhibin in bull testis from the infantile (4-5 wk of age) to postpubertal (49-56 wk of age) periods, testicular homogenates were obtained from animals of various ages and fractionated by a combination of immunoaffinity chromatography and SDS-PAGE. Subsequently, the fractions eluted from the SDS gels were assayed for total inhibin, inhibin A, and inhibin B by fluoroimmunoassay or immunofluorometric assays (IFMAs) and for inhibin bioactivity by an in vitro bioassay. The molecular mass patterns of inhibin A and inhibin B in the testis, as determined by the dimer-specific IFMAs, showed the presence of a peak of approximate 47 kDa until 21-26 wk of age. However, the peak disappeared after 31-32 wk of age. As bulls aged, especially after 31-32 wk of age, inhibin A and inhibin B levels increased in the molecular mass region of 27-34 kDa. Total inhibin showed two peaks, of between 20 and 26 kDa and at approximately 47 kDa, until 21-26 wk of age and a single peak between 20 and 30 kDa after 31-32 wk of age. The eluted fractions corresponding to 29, 31, or 47 kDa gave a dose-response curve that was parallel to the curve generated with 32-kDa inhibin A or 29-kDa inhibin B standard in the IFMA for inhibin A or inhibin B. The fractions corresponding to 29 and 31 kDa suppressed basal release of FSH from rat pituitary cells, but the 47-kDa fraction had a lower FSH-suppressing activity. In the testes of older bulls, immunoblot analysis revealed the presence of a 29-kDa band cross-reacting with inhibin alpha and inhibin betaB antibodies and of a 31-kDa band cross-reacting with inhibin alpha and inhibin betaA antibodies. The 47-kDa band was recognized by the alpha, betaA, and betaB antibodies. Immunohistochemisty of the testis at each age showed that inhibin alpha subunits were found exclusively in Sertoli cells, but the intensity of immunostaining diminished in older bulls, in parallel with the decrease in the testicular concentrations of total inhibin. We conclude that 1) bovine Sertoli cells produce both inhibin A and inhibin B, 2) inhibin production in Sertoli cells during the prepubertal period is characterized by the 47 kDa inhibin-related material that contains precursor forms of inhibin A and inhibin B, and 3) the proportion of the mature forms of inhibin A and inhibin B increases as bulls age, although total inhibin production in Setroli cells decreases.

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

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