Profiles of luteinizing hormone, follicle-stimulating hormone, testosterone and prolactin in rams of diverse breeds: effects of contrasting short (8L:16D) and long (16L:8D) photoperiods

Mature rams of Polled Dorset, Finnish Landrace, Rambouillet and Suffolk breeding were maintained in a temperature-controlled environment and exposed to two consecutive cycles of short (8L:16D) followed by long (16L:8D) days. Serum hormone concentrations were determined in weekly samples and in 24-h profiles characterized at the end of each lighting schedule (i.e., 12, 24, 36 and 48 weeks). In all four breeds, the pituitary-testicular axis was more active during short days as compared with long days and the magnitudes of changes in serum luteinizing hormone (LH), follicle-stimulating hormone (FSH) and testosterone concentrations were greater for the two most seasonal breeds, Finnish Landrace and Suffolks. In comparison to other breeds, Finnish Landrace rams had significantly (P less than 0.05) higher mean LH levels, showed the greatest number of LH peaks/24 h, and had the highest mean testosterone levels at the end of both periods of short days, while Rambouillet rams had significantly (P less than 0.05) lower testosterone. Rambouillets also showed the smallest changes in pulsatile LH and testosterone secretion and displayed the least number of LH peaks/24 h following short days. Serum FSH levels were significantly (P less than 0.05) higher in Finnish Landrace and Suffolk rams than in Polled Dorsets and Rambouillets after 12 weeks of short days. Breed differences in serum LH, FSH and testosterone were not apparent following long days. Prolactin levels in Rambouillet rams were significantly (P less than 0.05) lower than in the other breeds following both periods of long days. These results indicate that breed differences exist in mature rams with regard to hormone secretory profiles. Breed differences in serum gonadotropin and testosterone are only apparent during short days when the hypothalamo-pituitary-testicular axis in rams is considered most active. Likewise, breed differences in prolactin are noticeable only during long days when secretion of this hormone is enhanced. Breed differences in LH, FSH and testosterone secretion in rams during short days might be related to seasonality of mating and/or fecundity of breed types.     

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.     

Short-term pituitary-testicular responses of prepubertal ram lambs to hemicastration

To examine the short-term effects of hemicastration on pituitary-gonadal responses, 12 ram lambs were anesthetized and hemicastrated at 4 mo of age and killed (n = 4) at 2 (HC2), 7 (HC7), or 14 (HC14) days following surgery. Four intact (INT) rams were killed 14 days following anesthesia. Testis and pituitary weights were similar between HC and INT rams. Serum follicle-stimulating hormone (FSH) in HC rams increased within 6 h, peaked at 12 h, and remained elevated above INT levels throughout the study. Overall mean serum testosterone levels in HC rams were lower than in INT rams for the first 48 h, but were similar by 3 days post-surgery. Pulsatile luteinizing hormone (LH) and testosterone secretion was suppressed for the first 9.5 h following anesthesia and/or surgery in both HC and INT animals. A single LH pulse and succeeding testosterone pulse occurred in 10/12 HC and 4/4 INT rams between 10 and 14 h post-surgery, both of which were lower in amplitude in HC than INT animals. However, on Day 7, pulsatile secretory patterns of LH and testosterone were similar, suggesting compensatory androgen secretion had occurred in HC rams. Pituitary LH content was unaffected by hemicastration. In contrast, pituitary FSH content was greater in HC7 and HC14 compared to HC2 and INT animals. Pituitary gonadotropin hormone-releasing hormone (GnRH) receptor concentrations were similar in INT, HC7, and HC14 rams, but were slightly reduced in HC2 rams. Neither testicular LH nor FSH receptor concentrations were altered by hemicastration at any time.(ABSTRACT TRUNCATED AT 250 WORDS)     

Measurement of dimeric inhibins and effects of active immunization against inhibin alpha-subunit on plasma hormones and testis morphology in the developing cockerel

Inhibins and activins are implicated as endocrine regulators of follicle-stimulating hormone production and of testicular steroidogenesis and spermatogenesis in mammals. The potential involvement of these proteins in cockerels was investigated by measurement of circulating inhibin A, inhibin B, total inhibin alpha-subunit immunoreactivity (ir-alpha), activin A, LH, FSH, and testosterone from the juvenile state through to sexual maturity. Plasma inhibin A remained low between 6 to 12 wk of age and increased approximately threefold (P < 0.05) to a prepubertal peak between Weeks 14 to 18, followed by a gradual decline to the end of the study (Week 24). Although plasma FSH levels were not correlated to inhibin A before Week 16 (r = -0.17), they were negatively correlated from Week 18 (r = -0.49; P < 0.005). Inhibin B levels were below the assay detection limit until 16 wk of age but thereafter rose steadily in parallel with FSH (r = 0.27; P < 0.02) and testosterone (r = 0.35; P < 0.005). Thus, inhibins A and B showed divergent profiles during sexual maturation. Plasma ir-alpha levels were much higher than dimeric inhibin levels throughout, although the relative difference varied with age. Plasma activin A levels were below the assay detection at all times. Juvenile cockerels were actively immunized against a synthetic chicken inhibin alpha-subunit peptide conjugate to determine effects on plasma hormones and on testicular weight, morphology, and activin A content. Immunization generated circulating antibodies that bound (125)I-bovine 32-kDa inhibin but did not affect plasma FSH or testosterone levels at any stage of development. However, immunization reduced postpubertal plasma LH levels (P < 0.05) and promoted increased testicular weight (24%; P < 0.01) and total testicular activin A content (42%; P < 0.001) at 24 wk. Testis weight of immunized birds was positively correlated with inhibin antibody titer (r = 0.61; P < 0.05). Live weight gain was not affected by immunization. Morphometric analysis of testis sections showed that inhibin immunization had no effect on the fractional volume of the seminiferous tubule wall, seminiferous tubule lumen, or interstitial tissue area. Likewise, seminiferous tubule surface area and surface area:volume ratios were not different from controls. These findings support differential roles for inhibins A and B in regulating the pituitary-testicular axis during sexual maturation in the cockerel but highlight the need for more detailed studies to distinguish between potential endocrine and local intragonadal roles of inhibin-related peptides and to elucidate the mechanism by which immunization against inhibin alpha-subunit promotes testis enlargement without raising plasma FSH.     

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.     

Expression and regulation of testicular inhibin alpha-subunit gene in vivo and in vitro

Inhibin, a gonadal peptide, selectively suppresses FSH release from the pituitary. The cDNAs coding for ovarian inhibin have been isolated and characterized. However, little is known about testicular inhibin. In this study we have isolated inhibin alpha-subunit cDNA from human testicular cDNA libraries and determined inhibin alpha-subunit mRNA levels in testes. The longest cDNA isolated from human testis was 1380 nucleotides long and contained a nucleotide sequence identical to that of human placental inhibin alpha-subunit and isolated human inhibin alpha-subunit gene, but different from human ovarian inhibin alpha-subunit in two amino acids in the signal peptide. A single 1.5-kilobase species of inhibin alpha-subunit mRNA was identified in the testes of several species. This mRNA was the same size as those in human ovary and placenta. The regulation of inhibin alpha-subunit mRNA in rat testis was next examined. The concentration of testicular inhibin alpha-subunit mRNA peaked between 20-25 days of age and gradually declined thereafter. Hypophysectomy decreased testicular inhibin alpha-subunit mRNA levels. Supplementation of hypophysectomized animals with FSH restored inhibin alpha-subunit mRNA levels to those in intact controls. By contrast, treatment with testosterone had no effect. Similarly, in Sertoli cell-enriched cultures, FSH, but not testosterone, increased inhibin alpha-subunit mRNA levels. We conclude that 1) human testicular inhibin alpha-subunit mRNA is similar to that of human ovary and placenta; and 2) inhibin alpha-subunit mRNA in Sertoli cells is regulated by FSH, but not testosterone, both in vivo and in vitro.     

Effects of gonadotropin-releasing hormone pulse-frequency modulation on luteinizing hormone, follicle-stimulating hormone and testosterone secretion in hypothalamo/pituitary-disconnected rams

The effects of changes in pulse frequency of exogenously infused gonadotropin-releasing hormone (GnRH) were investigated in 6 adult surgically hypothalamo/pituitary-disconnected (HPD) gonadal-intact rams. Ten-minute sampling in 16 normal animals prior to HPD showed endogenous luteinizing hormone (LH) pulses occurring every 2.3 h with a mean pulse amplitude of 1.11 +/- 0.06 (SEM) ng/ml. Mean testosterone and follicle-stimulating hormone (FSH) concentrations were 3.0 +/- 0.14 ng/ml and 0.85 +/- 0.10 ng/ml, respectively. Before HPD, increasing single doses of GnRH (50-500 ng) elicited a dose-dependent rise of LH, 50 ng producing a response of similar amplitude to those of spontaneous LH pulses. The effects of varying the pulse frequency of a 100-ng GnRH dose weekly was investigated in 6 HPD animals; the pulse intervals explored were those at 1, 2, and 4 h. The pulsatile GnRH treatment was commenced 2-6 days after HPD when plasma testosterone concentrations were in the castrate range (less than 0.5 ng/ml) in all animals. Pulsatile LH and testosterone secretion was reestablished in all animals in the first 7 days by 2-h GnRH pulses, but the maximal pulse amplitudes of both hormones were only 50 and 62%, respectively, of endogenous pulses in the pre-HPD state. The plasma FSH pattern was nonpulsatile and FSH concentrations gradually increased in the first 7 days, although not to the pre-HPD range. Increasing GnRH pulse frequency from 2- to 1-hour immediately increased the LH baseline and pulse amplitude. As testosterone concentrations increased, the LH responses declined in a reciprocal fashion between Days 2 and 7. FSH concentration decreased gradually over the 7 days at the 1-h pulse frequency. Slowing the GnRH pulse to a 4-h frequency produced a progressive fall in testosterone concentrations, even though LH baselines were unchanged and LH pulse amplitudes increased transiently. FSH concentrations were unaltered during the 4-h regime. These results show that 1) the pulsatile pattern of LH and testosterone secretion in HPD rams can be reestablished by exogenous GnRH, 2) the magnitude of LH, FSH, and testosterone secretion were not fully restored to pre-HPD levels by the GnRH dose of 100 ng per pulse, and 3) changes in GnRH pulse frequency alone can influence both gonadotropin and testosterone secretion in the HPD model.     

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

To determine the effect of neutralization of inhibin on sperm output, 12 Holstein bulls were paired by birth date and weight on Day 1 of age. Each bull was actively immunized against bovine inhibin alpha1-26 gly-tyr (bINH) conjugated to human alpha globulin (HAG, n = 6 bulls) or HAG alone (controls, n = 6) at 60 days of age; booster immunizations were administered at 90, 104, 124, 270, and 395 days of age. Body weights and scrotal circumferences were measured at the time of primary immunization and at 10 days after each booster. In addition, jugular blood was obtained at 60, 70, 100, 114, 134, 280, and 405 days of age, during the 3-wk sperm collection period, and during a 6-h blood-sampling period after sperm collection to determine bINH antibody titer and concentrations of FSH, LH, testosterone, and estradiol. Beginning at 405 days of age, sperm output was measured 3 days/wk for 3 wk with two successive ejaculates collected each day for a total of 18 ejaculates per bull. During Days 60-405 of age, the increase in titer of bINH antibodies, scrotal circumference, and serum concentration of FSH was greater (p < 0.01) for the bINH-immunized compared with control bulls. There were significant (p < 0.01) pair x treatment interactions for sperm output and serum FSH and LH concentrations. Specifically, bINH-immunized bulls for four of the six pairs had nearly 50% greater serum FSH concentrations and sperm output. For the remaining two pairs, sperm output was lower and FSH was either lower or only marginally higher in the bINH-immunized bulls compared with controls. Also, the control bulls for the two remaining pairs produced more sperm than all but one bINH-immunized bull, and had markedly higher serum LH concentrations than all other bulls. To summarize, enhancement of sperm output after immunization against inhibin depends on the subsequent increment in FSH concentrations. We conclude that inhibin suppresses spermatogenesis. Thus, methods to immunoneutralize inhibin may have merit as a therapeutic route to enhance sperm production in reproductively maturing bulls.     

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)     

Immunoactive inhibin as a marker of Sertoli cell function following cytotoxic damage to the human testis

Sertoli and Leydig cell functions were evaluated in men with testicular damage due either to cytotoxic chemotherapy (CCT) or radiotherapy (XRT). Serum immunoactive inhibin, follicle-stimulating hormone (FSH), luteinizing hormone (LH) and testosterone concentrations were measured in 15 men (19-50 years) who had received 6-10 courses of combination CCT (mustine, vinblastine, procarbazine and prednisolone) for Hodgkin's disease 1-8 years earlier and 18 men (21-49 years) who had undergone unilateral orchidectomy for testicular seminoma followed by XRT (30 Gy) to the remaining testis, 1-4 years earlier. Normal men (n = 16, 19-36 years) acted as controls. Median inhibin (422 U/l) and testosterone (16.0 nmol/l) levels in the CCT-treated group were not significantly different from controls, whereas median FSH (14.5 IU/l) and LH (10.0 IU/l) levels were higher (p less than 0.0001 and p less than 0.001) than normal (2.9 and 5.5 IU/l). The median inhibin/FSH (I/FSH) ratio in the patients was lower (p less than 0.0001) than in the controls (33.8 vs. 187.0) as was the testosterone/LH (T/LH) ratio (1.7 vs. 3.8, p less than 0.001). In the XRT-treated group, both median inhibin (194.5 U/l) and testosterone (12.7 nmol/l) levels were lower (p less than 0.0001 and p less than 0.01) than normal (532.8 U/l and 20.0 nmol/l) in the presence of greatly elevated FSH (26.0 IU/l) and LH (14.5 IU/l) levels. In conclusion, CCT-induced testicular damage is associated with subtle Sertoli and Leydig cell dysfunction demonstrated by the reduced I/FSH and T/LH ratios; however, compensatory mechanisms maintain normal testosterone and inhibin levels.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of vitamin A deficiency upon gonadotropin response to gonadotropin-releasing hormone

There is a monotypic change in basal serum gonadotropin levels following retinol treatment of chronically vitamin A-deficient (VAD) male rats. The present study was undertaken to investigate the hypothesis that the specific increase in serum follicle-stimulating hormone (FSH) represents a change in gonadotrope responsiveness to gonadotropin-releasing hormone (GnRH). To this end, a test dose of GnRH was given to VAD rats pre-, 5 days post-, and 10 days postreplacement of vitamin A (PVA). In VAD rats, basal serum FSH and luteinizing hormone (LH) levels were higher than those of controls. Increased LH/testosterone ratios, both in basal levels and in the secretory response to GnRH, suggested Leydig cell hyporesponsiveness in VAD animals. Both the FSH and LH responses to GnRH were maximal at 1 h, declining thereafter. Although the absolute increments in FSH and LH 1 h after GnRH in VAD rats were greater than in controls, the percent increase in FSH tended to be lower in VAD rats and to increase after vitamin A replacement. The specific enhancement of FSH release PVA became evident only when assessing total secretion of FSH and LH after GnRH. Luteinizing hormone response to GnRH increased PVA, but not significantly, while FSH secretion after GnRH increased both 5 and 10 days PVA, times during which basal FSH levels were also increasing. These changes in FSH secretion could not be attributed either to increases in endogenous GnRH or to changes in testosterone or estradiol levels. Basal serum androgen binding protein levels, elevated in VAD animals, did not respond to the acute increases in FSH after GnRH and remained high PVA, suggesting no acute change in Sertoli cell function. Thus, the PVA increase in FSH secretion unmasks a partial inhibition of the gonadotrope present in the retinol-deficient, retinoic acid-fed male rat.     

Changes in plasma inhibin levels following pulsatile gonadotrophin-releasing hormone therapy in a man with idiopathic hypogonadotrophic hypogonadism

Changes in circulating inhibin levels were related to changes in testosterone (T) and the gonadotrophins luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in a hypogonadotrophic hypogonadal man before and during pulsatile gonadotrophin-releasing hormone therapy which resulted in normal spermatogenesis. Before treatment, the plasma inhibin levels in the patient (210 +/- 50 U/l; mean +/- SD of four samples) were lower than in normal controls (552 +/- 150 U/l; p less than 0.01), as were T (1.1 nmol/l) and gonadotrophin (less than 1.0 IU/l) levels. Within 1 week of gonadotrophin-releasing hormone treatment, plasma LH (14.1 +/- 0.7 IU/l) and FSH (14.4 +/- 0.6 IU/l) reached supraphysiological levels. In response, T and inhibin concentrations increased progressively to reach high normal levels (27.7 +/- 1.6 nmol/l and 609 +/- 140 U/l) at 4 weeks, by which time the gonadotrophin levels stared to decline and gradually returned to the normal range between 12 and 24 weeks of treatment. There was a concomitant decrease in T and inhibin levels which remained within the normal range. The decline in the FSH level following the rise in testicular hormones was earlier and steeper than that of LH (37.5% decrease at 4 weeks vs. 30.4% at 12 weeks), suggesting that T and inhibin may act together to inhibit pituitary FSH secretion as opposed to LH secretion which is primarily controlled by T. It is concluded that, in man, during maturation of the pituitary-testicular axis, changes in circulating inhibin parallel those of T, and quantitatively normal inhibin secretion is dependent on gonadotrophin stimulation. FSH secretion may be regulated through negative feedback control, by both T and inhibin.     

Plasma LH,FSH, testosterone,and age at puberty in ram lambs actively immunized against an inhibin alpha-subunit peptide

Active immunization against inhibin has been shown to advance puberty and increase ovulation rate in ewe lambs; but in ram lambs, effects on puberty and sperm production are equivocal. The objective of the present study was to determine whether active immunization against an inhibin alpha-subunit peptide advances the onset of puberty in ram lambs. St. Croix hair sheep ram lambs were assigned to inhibin-immunized (n = 7) and control (n = 8) treatment groups. Lambs in the inhibin-immunized group were immunized against a synthetic peptide-carrier protein conjugate, alpha-(1-25)-human alpha-globulin (halpha-G), and control lambs were immunized against halpha-G. Lambs were immunized at 3, 7, 13, 19, 25, 31, and 37 weeks of age. On the day of immunization a blood sample was collected and lambs were weighed. Another blood sample was collected 1 week following each immunization. At 20 weeks of age additional blood samples were collected at 20 min intervals for 8h. Beginning at 20 weeks of age and at weekly intervals thereafter, scrotal circumference (SC) was measured and semen was collected using electroejaculation. A subsequent ejaculate was collected 1 week following onset of puberty, which was defined as the week of age when an ejaculate first contained > or =50 x 10(6) sperm cells. In control lambs, plasma alpha-(1-25)-antibody (Ab) was nondetectable. In inhibin-immunized lambs, alpha-(1-25)-Ab titer increased from 7 to 25 weeks of age and then plateaued at a level that varied (P<0.001) among animals. Body weight and SC of control and inhibin-immunized lambs were similar at the onset of puberty. At pubertal onset inhibin-immunized lambs were older than control lambs (31.9+/-0.5 vs. 29.5+/-0.7 weeks of age, P<0.05). Plasma FSH concentrations were similar in control and inhibin-immunized lambs from 3 to 38 weeks of age. Plasma LH levels were lower (P<0.01) in inhibin-immunized than control lambs. During the 8-h blood sampling period at 20 weeks of age, LH and testosterone concentrations were lower (P<0.05) in inhibin-immunized than control ram lambs, and the LH pulse frequency was similar in the two groups of animals. The decreased LH secretion is consistent with the immunoneutralization of a putative inhibin alpha-subunit-related peptide that stimulates LH secretion in ram lambs. Present findings show that active immunization against an inhibin alpha-peptide delays rather than advances puberty in ram lambs.     

Influence of the degree of stimulation of the pituitary by gonadotropin-releasing hormone on the action of inhibin and testosterone to suppress the secretion of the gonadotropins in rams

This experiment determined if the degree of stimulation of the pituitary gland by GnRH affects the suppressive actions of inhibin and testosterone on gonadotropin secretion in rams. Two groups (n = 5) of castrated adult rams underwent hypothalamopituitary disconnection and were given two i.v. injections of vehicle or 0.64 microg/kg of recombinant human inhibin A (rh-inhibin) 6 h apart when treated with i.m. injections of oil and testosterone propionate every 12 h for at least 7 days. Each treatment was administered when the rams were infused i.v. with 125 ng of GnRH every 4 h (i.e., slow-pulse frequency) and 125 ng of GnRH every hour (i.e., fast-pulse frequency). The FSH concentrations and LH pulse amplitude were lower and the LH concentrations higher during the fast GnRH pulse frequency. The GnRH pulse frequency did not influence the ability of rh-inhibin and testosterone to suppress FSH secretion. Testosterone did not affect LH secretion. Following rh-inhibin treatment, LH pulse amplitude decreased at the slow, but not at the fast, GnRH pulse frequency, and LH concentrations decreased at both GnRH pulse frequencies. We conclude that the degree of stimulation of the pituitary by GnRH does not influence the ability of inhibin or testosterone to suppress FSH secretion in rams. Inhibin may be capable of suppressing LH secretion under conditions of low GnRH.     

Luteinizing hormone release in intact and castrate rams is altered with immunoneutralization of endogenous estradiol

Changes in the dynamics of luteinizing hormone (LH) release in the adult ram following immunoneutralization of endogenous estradiol were investigated. Castrate rams were actively immunized against estradiol-6-bovine serum albumin for 7 months and then their patterns of episodic LH release and LH response to multiple injections of gonadotropin-releasing hormone (GnRH, two 5-micrograms doses given iv 2 h apart) were assessed (April). In comparison with control rams immunized against rabbit gamma globulin, estradiol-immunized rams (antibody titre approximately 1:5000) exhibited more frequent LH releases (11.7 +/- 0.3 vs. 9.3 +/- 0.8 pulses/8 h, P less than 0.05) and a greater LH response to the first GnRH injection (peak delta value 190 +/- 8 vs. 130 +/- 25 ng/mL, P less than 0.01). Estradiol antiserum collected from the castrate rams was used in the passive immunization of intact rams (antibody titre approximately 1:200) for 1 month (beginning mid-July). Although episodic LH release was always similar for control and immunized rams, testosterone levels in the latter group increased approximately 150%. In contrast with the castrate ram response, GnRH treatment (two 5-micrograms doses given iv 80 min apart) produced a "self-priming" effect on LH release in the intact rams, an effect that was dampened with estradiol immunoneutralization. Consequently, peak 2:peak 1 ratios for delta value and 80-min mean incremental increase were much smaller (P less than 0.01) for the immunized rams (approximately 2:1 vs. 4:1 for the control rams).(ABSTRACT TRUNCATED AT 250 WORDS)     

Evidence for a major role of inhibin in the feedback control of FSH in the male rat

Adult rats (16-18/group) received a single intratesticular injection of 25, 100 or 400 microliters glycerol solution (7:3 in distilled water, v/v). Half of the rats in each group were given implants of testosterone, a testosterone-filled Silastic capsule (1.5 cm length) to provide serum values of testosterone within the normal range. After 1 week all animals were killed by decapitation. Serum concentrations of gonadotrophins, testosterone and immunoactive inhibin as well as testicular concentrations of testosterone and bioactive inhibin were determined. Testicular histology was studied in Paraplast-embedded tissue stained with PAS and haematoxylin-eosin. Glycerol treatment caused a dose-dependent ablation of spermatogenesis in a distinct area around the site of injection. Serum concentrations of FSH increased proportionally with increasing spermatogenic damage while serum LH and testosterone remained unaltered except with the highest glycerol dose. The rise in serum FSH was significantly correlated with serum (r = -0.70, P less than 0.001) and testicular (r = -0.66, P less than 0.001) concentrations of inhibin. A less pronounced correlation was found between LH and serum inhibin (r = 0.48). No correlation was found between the concentrations of LH and testicular inhibin or between serum concentrations of FSH and serum testosterone in the 25 and 100 microliters groups. Maintenance of low to normal serum testosterone concentrations by means of Silastic implants blocked the elevation of FSH in glycerol-treated animals but failed to affect significantly serum FSH in untreated rats. In all testosterone treated rats testicular inhibin concentrations were markedly reduced in the presence of lowered concentrations (7-14%) of testicular testosterone and unaltered serum FSH concentrations.     

Active immunization of gilts against gonadotropin-releasing hormone: effects on secretion of gonadotropins, reproductive function, and responses to agonists of gonadotropin-releasing hormone

Sexually mature gilts were actively immunized against gonadotropin-releasing hormone (GnRH) by conjugating GnRH to bovine serum albumin, emulsifying the conjugate in Freund's adjuvant, and giving the emulsion as a primary immunization at Week 0 and as booster immunizations at Weeks 10 and 14. Antibody titers were evident by 2 wk after primary immunization and increased markedly in response to booster immunizations. Active immunization against GnRH caused gonadotropins to decline to nondetectable levels, gonadal steroids to decline to basal levels, and the gilts to become acyclic. Prolactin concentrations in peripheral circulation were unaffected by immunization against GnRH. The endocrine status of the hypothalamic-pituitary-ovarian axis was examined by giving GnRH and two agonists to GnRH and by ovariectomy. An i.v. injection of 100 micrograms GnRH caused release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in control animals, but not in gilts immunized against GnRH. In contrast, administration of 5 micrograms D-(Ala6, des-Gly-NH2(10] ethylamide or 5 micrograms D-(Ser-t-But6, des-Gly-NH2(10] ethylamide resulted in immediate release of LH and FSH in both control and GnRH-immunized gilts. Circulating concentrations of LH and FSH increased after ovariectomy in the controls, but remained at nondetectable levels in gilts immunized against GnRH. Prolactin concentrations did not change in response to ovariectomy. We conclude that cyclic gilts can be actively immunized against GnRH and that this causes cessation of estrous cycles and inhibits secretion of LH, FSH, and gonadal steroids.(ABSTRACT TRUNCATED AT 250 WORDS)     

Evidence that testosterone and follicular fluid do not interact in the control of FSH secretion in rams

The hypothesis that testosterone and inhibin interact in the control of FSH secretion in rams was tested. Adult rams were castrated and were simultaneously given testosterone implants and 3-times daily sc injections of 0, 0.4, 0.8 or 1.6 ml charcoal-treated bovine follicular fluid (bFF). After 1 wk, the implants were removed, and the bFF injections continued as before. Blood samples were taken daily for mean LH, FSH and testosterone concentrations, and every 10 min for 12 h in the presence and in the absence of testosterone for assessment of pulsatile LH release. The bFF specifically inhibited FSH secretion from rat pituitary cells in culture. In the presence of testosterone, there were no main effects of bFF on mean plasma FSH or LH concentrations, nor were these values different from their pre-treatment means (P>0.05). Treatment with bFF did not affect LH pulse frequency or amplitude, but the number of rams showing LH pulses was reduced in the 0.8 and 1.6-ml dose groups (P<0.05). Removal of testosterone increased (P<0.05) both gonadotropins. In the absence of testosterone, no main effect of bFF on mean LH or FSH concentrations was observed, although the 1.6-ml dose suppressed the postcastration rise of both LH and FSH. These data suggest that inhibin does not interact with testosterone and that a physiological level of testosterone is sufficient for the regulation of FSH secretion in adult rams.     

Inhibin B,follicle stimulating hormone,luteinizing hormone and testosterone during childhood and puberty in males: changes in serum concentrations in relation to age and stage of puberty

Inhibin B is a gonadal dimeric polypeptide hormone that regulates synthesis and secretion of follicle stimulating hormone (FSH) in a negative feedback loop. The aim of the present study was to determine changes in serum inhibin B, gonadotropins and testosterone concentrations during childhood and puberty in males. We studied the relationship between circulating inhibin B, gonadotropins and testosterone in serum of healthy boys during the first two years of life and then in pubertal development. Using a recently developed two-side enzyme-linked immunosorbent assay (ELISA), inhibin B levels were measured in the serum of 78 healthy boys divided into eleven age groups from birth to the end of pubertal development. In addition, serum levels of gonadotropins and testosterone were measured. Serum inhibin B, gonadotropins and testosterone increased during the first months of postnatal life. A peak in serum inhibin B and gonadotropins concentrations was observed around 3-4 months of age. There was a significant positive correlation between serum inhibin B and gonadotropins and testosterone levels during the first 2 years of life. After this early increase, serum inhibin B, gonadotropins and testosterone levels decreased significantly and remained low until puberty followed by an increase beginning with the onset of puberty. Serum levels of inhibin B reached a peak at stage G3 of puberty. Around midpuberty, inhibin B lost its positive correlation with luteinizing hormone (LH) and testosterone from early puberty, and developed a strong negative correlation with FSH, which persisted into adulthood. We conclude that inhibin B plays a key role in the regulation of the hypothalamic-pituitary-gonadal hormonal axis during male childhood and pubertal development. Inhibin B is a direct marker of the presence and function of Sertoli cells and appears to reflect testicular function in boys.     

Impact of 900 MHz electromagnetic field exposure on main male reproductive hormone levels: a Rattus norvegicus model

This work analyzes the effects of radiofrequency-electromagnetic field (RF-EMF) exposure on the reproductive system of male rats, assessed by measuring circulating levels of FSH, LH, inhibin B, activin B, prolactin, and testosterone. Twenty adult male Sprague–Dawley rats (180?±?10 g) were exposed to 900 MHz RF-EMF in four equal separated groups. The duration of exposure was 1, 2, and 4 h/day over a period of 30 days and sham-exposed animals were kept under the same environmental conditions as the exposed group except with no RF-EMF exposure. Before the exposure, at 15 and 30 days of exposure, determination of the abovementioned hormone levels was performed using ELISA. At the end of the experiment, FSH and LH values of the long time exposure (LTE) group were significantly higher than the sham-exposed group (p?p?p?相似文献