Testosterone, luteinizing hormone, follicle stimulating hormone, and prolactin response to unilateral castration in prepubertal Holstein bulls

Hemicastration of Holstein bulls at 3 months of age resulted in increased (P<0.005) testicular weitht and testis sperm cell content at 330 days after treatment, but did not alter sperm cell concentration in the remaining hypertrophied testis. Radioimmuroassay of blood hormones at 1, 6, 12, and 24 weeks after treatment revealed that unilateral castration did not alter (P>0.1) basal levels or GnRH response profiles of either LH or testosterone compared to intact bulls. Hemicastration caused FSH to be elevated (P<0.01) compared to intact bulls at all sampling periods in both unstimulated and GnRH stimulated bulls. Prolactin varied with season and was greater (P<0.001) in hemicastrated bulls than in intact bulls at 1 and 6 weeks after treatment. Results indicate that unilateral castration at 3 months of age caused testicular hypertrophy of both steroidogenic and gametogenic function and this phenomena may be triggered by increased FSH or prolactin secretion, or both. Further, results indicate different testicular regulation mechanisms exist for pituitary LH and FSH release in bulls.     

Effect of uni- and bilateral cryptorchidism on testicular inhibin and testosterone secretion in rats

The effect of uni- and bilateral cryptorchidism on testicular inhibin and testosterone secretion and their relationships to gonadotropins were studied in rats. Mature Wistar male rats weighing approximately 300 g were made either uni- or bilaterally cryptorchid. Testicular inhibin and testosterone content and plasma levels of LH and FSH were examined 2 weeks later. A similar remarkable decrease in testicular inhibin content was found in uni- and bilaterally cryptorchid testes. On the other hand, the testicular testosterone content was significantly decreased only in unilaterally cryptorchid testis with an inverse increase in the contralateral testis. Plasma testosterone levels were normal and plasma LH and FSH increased significantly in both of the cryptorchid groups. These results showed that cryptorchidism impairs both Sertoli and Leydig cell functions. While testosterone production was compensated by increased LH for 2 weeks, neither inhibin secretion nor storage changed in cryptorchid or contralateral testes during the same period.     

Effects of testosterone on testicular inhibin and fluid production in intact and hypophysectomized adult rats

Rats were given s.c. implants of high (HT) or low (LT) doses of testosterone and 10 days later hypophysectomy or sham-operation was performed. The rats were killed after 50 days. Unilateral efferent duct ligation was performed 16 h before death to measure seminiferous tubule fluid production and the increment in testicular inhibin values (inhibin production). Inhibin levels in testis cytosols were measured by a pituitary cell culture bioassay. The LT implants maintained serum testosterone at control values and decreased testicular weight whereas HT implants raised serum testosterone 3-fold and maintained testicular weight at 75-85% of pretreatment levels. In intact rats, LT implants caused no change in testicular inhibin content but decreased inhibin production; no significant changes occurred with HT implants. After hypophysectomy both values were significantly suppressed and could not be maintained by HT or LT implants. However, the HT implants partly restored inhibin production despite their inability to influence testicular inhibin content. In contrast, tubule fluid production depended mainly on intratesticular testosterone levels and occurred normally in intact or hypophysectomized rats with HT but not LT implants. These results indicate that inhibin and seminiferous tubule fluid production, both functions of the Sertoli cell, are under different hormonal control. The maintenance of inhibin production by the testis requires the support of pituitary hormones, presumably FSH, while seminiferous tubule fluid production requires testosterone, presumably through LH stimulation of Leydig cells. These findings are consistent with the hypothesis that inhibin is produced in response to trophic stimulation by FSH.     

Testosterone response of cryptorchid and hypophysectomized rats to human chorionic gonadotrophin (hCG) stimulation

The testosterone responses to a single injection of hCG (100 i.u.) in hypophysectomized (hypox.), cryptorchid or sham-operated rats were followed over a 5-day period. In sham-operated rats, hCG induced a biphasic rise in serum testosterone, peaks being observed at 2 and 72 h. Reduced testis weights, elevated FSH and LH levels and reduced serum testosterone levels were found after 4 weeks of cryptorchidism, but hCG stimulation resulted in a normal 2 h peak in serum testosterone. However, the secondary rise at 72 h in cryptorchid rats was significantly lower than sham-operated rats. Reduced testis weight and undetectable serum FSH and LH levels together with decreased testosterone levels were found 4 weeks after hypophysectomy. Serum testosterone levels rose 2 h after hCG in comparison to hypox. controls but this peak was significantly reduced compared with sham-operated rats. The second rise in serum testosterone began on day 2, peaking on day 4 at levels comparable to that seen in sham-operated rats after hCG. The in vitro basal and hCG stimulated secretion of testosterone by cryptorchid testes was greater than that secreted by normal rat testes (518.0 +/- 45.9 and 3337.6 +/- 304.1 pmol per testis per 4 h compared with 223.6 +/- 24.9 and 1312.9 +/- 141.4 pmol per testis per 4 h for normal rat testes). In cryptorchid animals a single injection of 100 i.u. hCG resulted in a pattern of in vitro refractoriness similar to normal rats, lasting from 12 h to 2 days, during which testosterone secretion was reduced to near basal levels. The in vitro basal and hCG-stimulated secretion of testosterone by hypox. rat testes was severely diminished compared with normal rat testes. The temporal pattern of in vitro secretion of testosterone from hypox. rat testes mimicked the in vivo serum testosterone pattern seen in these animals. This study demonstrates important differences in the in vivo and in vitro testosterone response to hCG after testicular damage.     

Effects of intermittent pulsatile infusion of luteinizing hormone-releasing hormone on dihydrotestosterone-suppressed gonadotropin secretion in castrate rams

The feedback effects of dihydrotestosterone (DHT) on gonadotropin secretion in rams were investigated using DHT-implanted castrate rams (wethers) infused with intermittent pulsatile luteinizing hormone-releasing hormone (LHRH) for 14 days. Castration, as anticipated, reduced both serum testosterone and DHT but elevated serum LH and follicle-stimulating hormone (FSH). Dihydrotestosterone implants raised serum DHT in wethers to intact ram levels and blocked the LH and FSH response to castration. The secretory profile of these individuals failed to show an endogenous LH pulse during any of the scheduled blood sampling periods, but a small LH pulse was observed following a 5-ng/kg LHRH challenge injection. Dihydrotestosterone-implanted wethers given repeated LHRH injections beginning at the time of castration increased serum FSH and yielded LH pulses that were temporally coupled to exogenous LHRH administration. While the frequency of these secretory episodes was comparable to that observed for castrates, amplitudes of the induced LH pulses were blunted relative to those observed for similarly infused, testosterone-implanted castrates. Dihydrotestosterone was also shown to inhibit LH and FSH secretion and serum testosterone concentrations in intact rams. In summary, it appears that DHT may normally participate in feedback regulation of LH and FSH secretion in rams. These data suggest androgen feedback is regulated by deceleration of the hypothalamic LHRH pulse generator and direct actions at the level of the adenohypophysis.     

Effects of inhibin on the in vitro synthesis of desoxyribonucleic acid in the rat testis

Three preparations of inhibin extracted from ram rete testis fluid (RTF) and from human seminal plasma (HSP) reduce tritiated thymidine incorporation into testicular desoxyribonucleic acids (DNA) in vitro. Effect of low molecular inhibin from RTF is dose-dependent. Castrated ram serum does not modify testicular DNA synthesis in vitro. Besides their suppressive action on follicle stimulating hormone (FSH) secretion in vivo and in vitro, these inhibin preparation display a direct inhibiting effect on testicular DNA synthesis and, thus, on mitotic activity. Identity between inhibin and testicular chalones are discussed.     

The effect of cryptorchidism and subsequent orchidopexy on testicular function in adult rats

Cryptorchidism for 28 or 10 days resulted in a severe disruption of spermatogenesis (assessed histologically or by fertility tests), Sertoli cell function (assessed by seminiferous tubule fluid production after efferent duct ligation, ABP levels, binding of 125I-labelled FSH to testis homogenates and serum FSH levels) and Leydig cell function (assessed by serum LH and testosterone levels, in-vitro testosterone production, binding of 125I-labelled hCG). Orchidopexy after 28 days of cryptorchidism resulted in a poor recovery of spermatogenesis since the majority of tubules were lined by Sertoli cells and a few spermatogonia. No recovery occurred in the indicators of Sertoli and Leydig cell function. Orchidopexy after 10 days of cryptorchidism also resulted in a poor recovery of spermatogenesis, with a few animals showing partial recovery after 6 months. No recovery occurred in seminiferous tubule fluid production but partial recovery occurred in ABP content and production rate. Serum FSH, LH levels and in-vitro testosterone production by the testis remained elevated and did not change from the values found during cryptorchidism. Fertility testing at 6 months revealed a small number of rats in which fertility was restored although the number of embryos was lower than in controls. In this group of animals there was a significant improvement in a number of indicators of Sertoli cell and Leydig cell function. These data provide further evidence to link the changes in Sertoli cell and Leydig cell function to the germ cell complement present in the testis.     

Serum luteinizing hormone follicle-stimulating hormone and prolactin in neonatal-androgenized rats.

Serum levels of LH, FSH, Prolactin and Testosterone of 90 days old male rats androgenized soon after birth were determined by specific radioimmunoassay and were compared to untreated rats. LH and FSH levels were also determined in 90 days old female rats neo-natally treated with testosterone and compared with normal diestrus rats. Androgenization of male rats significantly increased serum FSH and Prolactin levels without producing changes in plasma LH and testosterone concentrations. Similar increase in the FSH levels were found in androgenized female rats although plasma FSH concentrations were lower than in the male groups. These results obtained in male rats give an additional evidence that androgens acting in the first days of life are responsible of the higher levels of FSH and Prolactin that characterize the male or tonic pattern of gonadotrophin secretion.     

Effects of the induction of experimental cryptorchidism and subsequent orchidopexy on testicular function in immature rats

Cryptorchidism surgically induced in 14-day-old rats, was allowed to persist until 35 days when one group was killed to assess testicular function. In a second group the cryptorchid testis was returned to the scrotum surgically (orchidopexy) and subsequently killed at 130 days. A third group remained persistently cryptorchid to 130 days, while in a fourth group two sham operations were performed at 14 and 35 days. At 35 days, cryptorchidism resulted in a significant decline in testis weight due to suppressed spermatogenesis. Sertoli cell function as measured by seminiferous tubule fluid (TF) production after unilateral efferent duct ligation and androgen-binding protein (ABP) production was significantly depressed in the cryptorchid group. Serum follicle-stimulating hormone (FSH) and luteinizing hormone (LH) levels were significantly elevated with cryptorchidism but serum testosterone levels were unchanged. Although morphometric measurements showed no change in Leydig cells cross-sectioned area, in vitro human chorionic gonadotropin (hCG)-stimulated testosterone production was significantly increased in the cryptorchid group at higher hCG doses. Similar changes were found in cryptorchid testes at 130 days except that Leydig cell cross-sectional area was now significantly increased. Orchidopexy at 35 days restored spermatogenesis and fertility during test mating was not impaired. TF production, ABP accumulation and serum FSH levels returned to normal following orchidopexy.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of follicle-stimulating hormone on inhibin release by different testicular compartments in the adult ram.

The aim of this study was to determine the bidirectional release of immunoreactive inhibin-alpha (irINH-alpha) by different testicular compartments in the adult ram and to assess the effects of FSH on the distribution of inhibin in the testis. Immunoreactive INH-alpha was measured by RIA in fluid samples collected concurrently from the three testicular compartments--the seminiferous tubules, the interstitium, and the vascular system--through catheters inserted surgically into the rete testis, testicular lymphatic duct system, and spermatic veins, respectively. Overall, the concentration of irINH-alpha in rete testis fluid was 25 times the level in testicular lymph and over 500 times the concentration in peripheral blood. The pattern of irINH-alpha concentration in rete testis fluid was inversely related to that in testicular lymph, but i.v. administration of FSH had a decoupling effect on this relationship by depressing inhibin concentration in testicular lymph without affecting inhibin levels in rete testis fluid. Nevertheless, increased flow of testicular lymph more than compensated for the transient fall in irINH-alpha concentration so that, overall, the total output of inhibin via the testicular lymphatic duct system (and the vascular system) increased significantly. No persistent or significant changes were observed in the flow rate of rete testis fluid or concentration of irINH-alpha in the fluid after administration of FSH. The time frame for the response of the testis to FSH is indicative of the involvement of a mediator. Electrophoretic analysis of serially collected testicular lymph samples consistently revealed an FSH-induced release of a series of proteins in the M(r) range of 30,000-32,000.(ABSTRACT TRUNCATED AT 250 WORDS)     

Temporal changes in rat Leydig cell function after the induction of bilateral cryptorchidism

Adult rats were made bilaterally cryptorchid and studied at intervals of 3, 7, 14 or 21 days to study temporal changes in Leydig cell function. Serum FSH and LH levels were measured and the cross-sectional area of the Leydig cells assessed by morphometry. The function of the Leydig cells was judged by the binding of 125I-labelled hCG to testicular tissue in vitro and the testosterone response of the testis to hCG stimulation in vitro. By 3 days after cryptorchidism, the binding of labelled hCG to testicular tissue was significantly decreased compared to that of controls, but the testes were able to respond to hCG stimulation in vitro. At 7, 14 and 21 days after cryptorchidism, an enhanced testosterone response was observed and the size of the Leydig cells was significantly greater than that of the controls, which indicated increased secretory activity by the cryptorchid testis. Although serum FSH levels were significantly elevated after 3 days of cryptorchidism, serum LH levels did not rise until 7 days, thereby suggesting that the loss of receptors is unlikely to result from down-regulation by LH. The reduced testosterone response of the cryptorchid testis in vivo to low doses of hCG and the enhanced response at high doses are probably related to the reduced blood flow to the cryptorchid testis and the decreased sensitivity of the Leydig cells induced by LH/hCG receptor loss.     

Disruption of seminiferous epithelial function in the rat by ovarian protein

The granulosa cell produces an inhibitor of aromatase activity, which recently was purified to homogeneity (follicle-regulatory protein: FRP). Since extracts of testicular homogenates also contain factor(s) with biological properties similar to FRP, including inhibition of granulosa cell aromatase, we examined the effects of ovarian FRP on testicular function. Forty-five-day-old rats received daily FRP injections (100 micrograms or 300 micrograms). After 15, 30, 45, and 70 days of therapy, (n = 5 each group), trunk serum was measured for testosterone, androstenedione, estradiol, and FSH levels by established radioimmunoassays (RIA). One testis from each rat was homogenized, centrifuged, and evaluated for sperm head counts; the other testis was dissected by transillumination, and the length of seminiferous epithelial stages determined. After 15 (control: 4.8 +/- 0.2 mm; 100 micrograms: 6.0 +/- 0.3 mm; 300 micrograms: 6.6 +/- 0.3 mm) and 30 days (control: 4.6 +/- 0.2 mm; 100 micrograms: 6.3 +/- 0.2 mm; 300 micrograms: 5.9 +/- 0.2 mm) of treatment the length of the "strong" seminiferous tubule segment in FRP-treated rats was greater than in control rats (p less than 0.05). Serum levels of steroids and FSH were similar in all groups. After 30, 45, and 70 days of treatment, the sperm head counts for the 100-micrograms and 300-micrograms dosages were 26%, 29%, 30% and 20%, 34%, and 24% of control values, respectively. By 70 days of treatment, cycle Stage VII was markedly reduced or absent in FRP-treated rats, and their round spermatids contained ring chromatin; both conditions indicate degeneration. FRP (50 micrograms/ml) was added to rat Sertoli cell cultures for 4 days after which transferrin and androgen-binding protein (ABP) were measured. FRP enhanced Sertoli cell secretion of ABP (58 vs. 138 +/- 7 microliters eq/culture) and transferrin (2.1 vs. 4.7 +/- 0.6 microgram/culture). In conclusion, systemic injection of FRP alters seminiferous epithelial function by reducing maturation of mature sperm forms. Adding FRP to Sertoli cells in culture enhances secretion of transferrin and ABP; this suggests that maturation of the germinal elements may be linked to the secretory function of seminiferous tubules.     

The effects of methyltestosteone on reproductive function in male greyhounds

Oral administration of methyltestosterone (MT) at 50 mg/dog/day to intact adult male greyhounds for 90 d resulted in decreased (P < 0.05) mean daily sperm output and mean testicular length. Additionally, the mean diameter of seminiferous tubules in MT-treated dogs tended to decrease (P = 0.08). Mean concentrations of luteinizing hormone (LH) and follicle stimulating hormone (FSH) and concentrations of testosterone in serum were also decreased or tended to decrease (P = 0.0003 to 0.059) at various sampling periods during MT treatment, suggesting alterations in spermatogenesis resulted from decreased serum concentrations of gonadotropins and steroids. Mean daily sperm output, mean testicular length, mean seminiferous tubule diameter and mean concentrations of FSH in serum were not decreased (P > 0.05) at the end of a 90-d recovery period. However, mean concentrations of serum LH and concentrations of testosterone were still lower (P < 0.05) during five of six and one of six sampling times, respectively, during the recovery period than the pretreatment levels, suggesting a prolonged effect of MT treatment on the pituitary/gonadal axis.     

Human chorionic gonadotropin increases the concentration of macrophages in neonatal rat testis

The purpose of these studies was to determine whether treatment of newborn rats with exogenous FSH or hCG would alter the concentration or size of testicular macrophages. Animals were injected once daily with various doses of FSH, hCG, or vehicle for 8-10 days beginning the day following birth. After immunohistochemical labeling of the macrophages with a monoclonal antibody specific for rat macrophages, the concentration and size of macrophages were determined by use of a point-counting method. Body weight, testis weight, and serum levels of testosterone and FSH were also measured. It was found that hCG significantly increased the concentration of macrophages within the interstitium but did not affect the size of the cells. Both testicular weight and serum testosterone concentrations increased after hCG treatment. Although FSH increased the weight of the testis, neither the size nor concentration of macrophages was altered. These results raise the possibility that the number of macrophages within the interstitial compartment of the normally maturing rat testis is under the control of LH.     

Sperm production, testicular size, serum gonadotropins and testosterone levels in Merino and Corriedale breeds

The relationships between testis size, hormone secretion and sperm production were studied during the spring (December) and autumn (May) in rams of two breeds with different breeding seasons and body weights (Corriedale and Australian Merino) maintained on native pastures and under natural photoperiods in Uruguay. Blood samples were collected at 20-min intervals during a 260-360-min period in 13 rams (four Corriedale, nine Australian Merino) during the late spring and autumn. Rams were weighed and testis size was estimated by orchimetry at each time period. Sperm production was estimated during a 2-week period, 2 months before blood collection and during each week following every blood collection. There was no relationship between testicular size and sperm production measured at the same time, nor between live weight and sperm production. In contrast, testicular volume during the late spring was correlated with sperm production in the autumn (r = 0.65; P = 0.02). The autumn serum LH was higher in Corriedale than in Merino rams. LH pulsatility was unaffected by season, but LH pulse frequency tended to be higher in Corriedale than in Merino rams, particularly in the late spring (2.37 versus 1.56 pulses/6 h; P = 0.08). Serum testosterone concentration was similar in both breeds and seasons. FSH levels were higher in the late spring than in the autumn in both breeds (Corriedale: 2.83 +/- 0.48 versus 2.17 +/- 0.24 ng x mL(-1); Merino: 2.23 +/- 0.24 versus 1.88 +/- 0.17 ng x mL(-1)). FSH and testosterone concentrations during the late spring were positively correlated with autumn sperm production (P = 0.07 and P = 0.03, respectively). In conclusion, the present experiment suggests that LH secretion is not a good parameter for the prediction of sperm production. In contrast, in our conditions (breeds and native pastures) testicular size and testosterone or FSH concentrations from the late spring may be used to predict sperm production in the autumn.     

Effect of metronidazole on spermatogenesis and FSH, LH and testosterone levels of pre-pubertal rats

Metronidazole, a 5-nitroimidazole drug has been reported to decrease testicular weight, testicular and epididymal spermatid counts and causes abnormal sperm morphology with degeneration of seminiferous tubules with 6 weeks treatment of metronidazole (400 mg/kg, day). In contrast to DNA flow cytometry (FCM), the histological and gravimetric parameters do not allow a rapid, sensitive, objective and multiparameteric evaluation of reproductive toxicants on spermatogenesis. Moreover, the exact mechanisms for such an effect are not entirely clear. The present study was therefore undertaken to assess the effects of intraperitoneal (i.p.) administration of metronidazole 400 mg/kg daily for 30 days on testicular germ cell changes assessed by DNA (FCM) and hormone levels of testosterone, FSH and LH in pre-pubertal rats. A significant reduction in the haploid cell population in metronidazole treated groups as compared to saline treated controls was observed. The mean serum FSH, LH and testosterone value were also lowered in treated animals. Thus, the spermatotoxic effects of metronidazole were probably mediated by decrease in the circulating hormones responsible for spermatogenesis.     

Alteration of free sulphydryl content of rat sperm heads by suppression of intratesticular testosterone

Subcutaneous injections of testosterone propionate to adult male rats at a dose of 2.5 or 10 mg/kg body weight, 3 times per week for 7 weeks, resulted in a 75% reduction in serum LH and more than 50% reduction in intratesticular testosterone concentration, but serum FSH levels remained unchanged. The free -SH content, measured as iodo[14C]acetamide binding, increased by 70-100% in testicular sperm heads after suppression of testicular testosterone, and by 25-30% in caput epididymal sperm heads but was decreased by 70-80% in cauda epididymal sperm heads. These results demonstrate an alteration in the oxidative state of sperm nuclear basic proteins, suggesting incomplete nuclear maturation. These changes may be specific for the suppression of intratesticular testosterone, thus illustrating the androgen dependency of sperm head maturation. The contrast effects noted between the iodo[14C]iodoacetamide binding by the caput and the cauda epididymal sperm heads indicate that testosterone propionate treatment may affect the mechanisms regulating the oxidation of the sulphydryl residues in sperm heads during epididymal transit. This alteration may not directly relate to the tissue androgen concentrations.     

Seasonal changes in the endocrine responsiveness of the pituitary and tests of male sheep in relation to their patterns of gonadotropic hormone and testosterone secretion

Pituitary and testicular endocrine responses to exogenous gonadotropin releasing hormone (GnRH) and luteinizing hormone (LH), respectively, were assessed for adult rams in an investigation of the regulation of seasonal changes in the patterns of episodic LH and testosterone secretion. Concurrent variations in testis size and in circulating levels of follicle stimulating hormone (FSH) and prolactin (PRL) were also examined. On 10 occasions throughout the year, serum hormone levels were assessed over 6- to 8-h periods during which time rams were left untreated (day 1) or were injected (iv) with single doses of either 10 micrograms synthetic GnRH (day 2) or 30 micrograms NIH-LH-S18 (day 3); blood samples were collected from the jugular vein at 10- to 20-min intervals. Testicular redevelopment during the summer, as indicated by increasing testis diameter measurements, was associated with increases in mean FSH level and was preceded by a springtime rise in mean PRL level; "spontaneously" occurring LH pulses and those produced in response to GnRH treatment were relatively large during this period. Increases in the magnitude of testosterone elevations in response to both endogenously and exogenously produced LH pulses occurred in August. Mean testosterone levels were elevated fourfold in the fall as a consequence of relatively frequent and small LH pulses stimulating a more responsive testis to produce more frequent and larger testosterone elevations; endogenous LH pulses, however, did not appear to stimulate the testes maximally at this time.(ABSTRACT TRUNCATED AT 250 WORDS)     

The different mechanisms for suppression of pituitary and testicular function

The differential mechanisms reducing androgen secretion by LHRH agonists are discussed with relevance to clinical therapy. LH secretion can be desensitised by exposure to agonists using high doses, frequent injections or sustained release/constant infusion. The desensitized pituitary is refractory to hypothalamic stimulation. Pituitary receptor suppression is associated with depletion of pituitary gonadotrophin content, and a decline of LH and FSH secretion to a basal rate. Recovery of LH responsiveness to endogenous LHRH stimulation requires restitution of gonadotrophin content (about 7 days in rats). After long-term infusions in normal men, testosterone secretion recovers within 7-10 days. The binding capacity of testicular LH/hCG receptors is reduced in rats after supraphysiological gonadotrophin stimulation, by agonists or directly by hCG, concomitantly the steroidogenic capacity of the testis in vitro is impaired. Qualitative changes in androgen biosynthesis are a marked fall in testosterone production and dose-dependent enhancement of progesterone production. After 12 months of buserelin injections, the changes in hCG-stimulated rat testes are an increased ratio of progesterone/17-OH-progesterone (inhibition of 17-hydroxylase), a reduced capacity for secretion of androstenedione and testosterone (block of 17,20-desmolase), and increased 5 alpha-pregnane-3,20-dione (this steroid inhibits the 17,20-desmolase, similarly to progesterone). After treatment, Leydig cell function recovers completely. Leydig cell hyperplasia is observed as a result of the steroidogenic changes. These findings in rats have not been observed in dogs, monkeys or in humans.(ABSTRACT TRUNCATED AT 250 WORDS)     

Immunoneutralization of inhibin modifies hormone secretion and sperm production in bulls.

The objective of this study was to examine the role of endogenous inhibin in the regulation of FSH, LH, and testosterone secretion and sperm production in bulls. Bulls were actively immunized against bovine inhibin alpha 1-26 gly-tyr (bINH) conjugated to human alpha globulin (HAG) or HAG alone (controls) and emulsified in Freund's complete adjuvant. Primary immunization was at 14 wk of age, followed by booster immunizations in Freund's incomplete adjuvant at 28, 30, and 34 wk of age. Ten days after each booster immunization, scrotal circumferences and body weights were measured, and blood was sampled for determination of bINH antibody titer. Ten days after the third booster, blood was sampled at 1-h intervals for 8 h to quantify serum concentrations of FSH, LH, and testosterone. After this blood sampling period, bulls were castrated and testicular sperm production was determined. Serum diluted 1:4,000 from bINH-immunized bulls bound 36%, 52%, and 53% of radioiodinated bINH after the first, second, and third boosters, respectively. Serum from controls bound less than 1% radioiodinated bINH. After the third booster, serum concentrations of FSH and testosterone were increased (p less than 0.05) and LH concentrations were decreased (p less than 0.001) in bINH-immunized bulls compared with controls. After the third booster, daily sperm production per gram of testicular parenchyma was increased (p less than 0.05) in bINH-immunized bulls compared with controls. Scrotal circumferences and body weights were similar between treatment groups throughout the experiment. We concluded that inhibin has a role in regulation of secretion of gonadotrophins and testosterone and testicular sperm production, but not testicular growth, in bulls.(ABSTRACT TRUNCATED AT 250 WORDS)