Passive immunization of rams (Ovis aries) against GnRH: effects on antibody titer,serum concentrations of testosterone,and sexual behavior

The effect of immunoneutralization of gonadotropin-releasing hormone (GnRH) on serum concentrations of testosterone and sexual behavior was evaluated in sexually mature male sheep. In Experiment 1, GnRH1 rams (n=16) were passively immunized against GnRH (300 ml antiserum), control rams were either passively immunized against keyhole limpet hemocyanin (KLH, n=15) or surgically castrated (Wethers1, n=4). Sexual performance of the rams was assessed weekly for 3 weeks before and 6 weeks after immunization, using ovarihystertomized ewes actively immunized against GnRH. Experiment 2 evaluated the effects of repeated immunization. Rams were immunized with two aliquots (400 and 300 ml, respectively) of anti-GnRH sera (GnRH, n=5) or normal sheep serum (NSS, n=4), 2 weeks apart. Surgically castrated animals were used as a second control group (Wethers2). Administration of anti-GnRH sera, but neither anti-KLH nor NSS sera, resulted in marked reduction (P<0.05) in serum concentrations of testosterone. Sexual behavior was not consistently affected by administration of one aliquot of anti-GnRH sera, however repeated immunizations resulted in more persistent reduction in serum concentrations of testosterone and more consistent suppression of sexual behavior.     

Testicular development, ultrasonographic and histological appearance of the testis in ram lambs immunized against recombinant LHRH fusion proteins

Sixteen native ram lambs weaned at 10 wk of age were divided into two groups. Eight animals were immunized against LHRH with a mixture of two fusion proteins: ovalbumin-LHRH-7 and thioredoxin-LHRH-7. The immunized lambs received a primary immunization plus two booster immunizations at 4 and 12 wks. Animals in the control group (n=8) were not treated. Scrotal measurements and blood samples were taken at 2-week intervals. Beginning at 25 wk of age, semen was collected and sexual behaviour was evaluated on a weekly basis. At 35 and 37 wk of age testes and accessory glands of all animals were subjected to ultrasound scanning. At 37 wk of age animals were slaughtered and testes were evaluated histologically. Serum LHRH antibodies (P<0.01) were detected in animals of the immunized group which had reduced serum testosterone concentrations (P<0.01). Testicular development was suppressed in the immunized animals (P<0.01). Immunized animals exhibited mounting activity 5 wks later than control animals. No mature spermatozoa containing ejaculates were collected from immunized animals. Control animals had moderately echogenic ultrasonographic appearance at 37 wk age, whereas immunized animals had hypoechogenic images. Mean seminiferous tubule diameter in immunized lambs was significantly smaller than that in control lambs. Basal membrane was thickened and hyalinized; there was an increase in peritubular connective tissue. No proliferating spermatogonia or mature spermatozoa were present in the tubules in these animals. There were no differences in the ultrasonographic appearance of prostate and vesicular gland between control and immunized animals. The LHRH recombinant fusion proteins were effective in immunological castration in ram lambs when started at 10 wk of age as noted by differences in serum testosterone, testicular histology and ultrasonographic appearance of testis and weight of accessory sex glands. Determining the effects of immunization on ultrasonographic appearance of the testis related to time after immunization requires further investigations.     

Short- and long-term effects of immunization against gonadotropin-releasing hormone, using Improvac, on sexual maturity, reproductive organs and sperm morphology in male pigs

The objective of this study was to determine the short and long term effects of a gonadotropin-releasing hormone (GnRH) vaccine (Improvac™ Pfizer Ltd.), on sexual maturity, development of the reproductive organs, and the morphology of caudal epididymal spermatozoa in non-castrated male pigs. The pigs were slaughtered 4, 16 or 22 weeks after the second Improvac™ vaccination. A total of 80 crossbred non-castrated male pigs were included in this study comprising two experiments, a short-effect (Experiment 1) and a long-effect (Experiment 2). The first experiment included 56 pigs, 24 of them were maintained as controls and 32 were vaccinated twice, and slaughtered 4 weeks after the second vaccination. The second experiment included 24 pigs, 12 controls and 12 vaccinated twice, and slaughtered either 16 weeks (n = 6) or 22 weeks (n = 6) after the second vaccination. None of the immunized pigs was sexually mature at slaughter, i.e. 4, 16 or 22 weeks after second vaccination. Corresponding results of the control pigs showed that 50% had reached sexual maturity at the age corresponding to 4 weeks after the second vaccination, and 100% at slaughter 16, respectively, 22 weeks after vaccination. At 4, 16 and 22 weeks after second vaccination both testes weight and bulbourethral length were significantly reduced (p < 0.001). The percentages of proximal droplets and abnormal heads were significantly lower in the control pigs than in the immunized pigs at slaughter 4 weeks after vaccination, whereas distal droplets were higher. For the other morphological parameters no significant differences were seen, but all mean values except for acrosome defects were numerically lower in the control pigs compared with the immunized pigs. For pigs slaughtered 16 or 22 weeks after vaccination, the vaccination effect was significant for percentages of proximal droplets, distal droplets, acrosome defects, acrosome abnormality and abnormal heads (p = 0.017-0.001). The immunization clearly disrupted the number and morphology of the interstitial Leydig cells, lasting throughout the study period (4-22 weeks after vaccination). Spermatogenesis was also clearly affected in the immunized pigs, to various degrees, from mild disruption (spermatocyte loss, decrease of the normal number of layers of germ cells) to severe loss of germ cells including tubuli with Sertoli cells-only (complete disappearance of germ cells), also covering the entire study period. The results indicated that the effect of immunization persisted for at least 22 weeks after the second vaccination.     

GnRH immunocontraception of male cats

The development of nonsurgical contraceptives for cats may facilitate population control of the species. The purpose of this study was to investigate the utility of GnRH for immunocontraception of male cats. Male cats (n=12) were divided into groups of three and were immunized once with 0 (sham), 50, 200, or 400 microg synthetic GnRH coupled to keyhole limpet hemocyanin and combined with a mycobacterial adjuvant to enhance immunogenicity. GnRH antibody titer, serum testosterone concentration, and scrotal size were determined monthly. At 6 months, semen was collected by electroejaculation and testes were examined histologically. GnRH antibodies were detected in all cats receiving GnRH vaccine by 1 month post-treatment and persisted throughout the study. No dose effect of GnRH was observed; titers were not different among cats treated with 50, 200, or 400 microg GnRH (P=0.5). Six of nine treated cats were classified as responders based on high GnRH antibody titers (>32,000). By 3 months post-treatment, responder cats had undetectable testosterone concentrations and testicular atrophy. Nonresponder cats had GnRH titers of 4000-32,000 and testosterone concentrations intermediate between responder and sham-treated cats. At 6 months, total sperm counts were similar for sham-treated cats (3.1+/-1.8 x 10(6) sperm) and nonresponder cats (3.4+/-1.6 x 10(6) sperm; P=0.7). Only one of the six responder cats produced sperm, none of which were motile. Combined testicular weights of responder cats (1.3+/-0.1 g) were lower than sham-treated controls (5.3+/-1.3 g; P=0.02) and nonresponder cats (2.9+/-0.3 g; P=0.02). Histologic evaluation of the testes revealed that in responder cats, the interstitial cells that were present were pale and shrunken compared to the plump, polyhedral eosinophilic cells in sham-treated cats. GnRH responder cats had marked tubular atrophy with vacuolated Sertoli cells and a paucity of germ cells. Single-dose GnRH treatment resulted in testosterone concentrations and semen quality consistent with immunocastration in a majority of cats treated.     

Neutralization of gonadotropin-releasing hormone in neonatal rats with permanent impairment of the hypothalamic-pituitary-testicular axis

Males rats were passively immunized at 5 days of age with a single 0.25 ml i.p. injection of gonadotropin-releasing hormone (GnRH) antiserum. Control animals were given an equal volume of normal rabbit serum (NRS). Serial blood determinations of gonadotropins, testosterone and dihydrotestosterone (DHT) were obtained at intervals ranging from early in life through adult life. Gonadotropin secretion was reduced (P less than 0.025) up to 35 days of age. Androgen secretion (testosterone) was reduced (P less than 0.05) at 10 and 33 days of age. When hCG was given to 54-day-old (young adult), and 100-day-old and 15-month-old animals, testosterone concentrations were similar in both experimental and control groups 1 h after hCG stimulation. As adults, basal gonadotropins were the same in both groups; however, after GnRH stimulation, the GnRH antiserum-treated groups showed an increased gonadotropin response when compared to the NRS control group. In order to determine whether there was an alteration in steroid feedback, other animals were castrated at adult age (approximately 100 days old), and exogenous testosterone was given in increasing increments. However, serum gonadotropins decreased similarly in treated and control groups. These data indicate that a single injection of GnRH antiserum early in life decreased gonadotropin secretion temporarily during prepubertal sexual development and caused a permanent alteration in hypothalamic-pituitary-testicular function.     

Evaluation of the possible direct effects of gonadotrophin-releasing hormone analogues on the monkey (Macaca mulatta) testis

In Exp. 1, the effect of treatment with a GnRH agonist on basal concentrations of serum testosterone and peak values of serum testosterone after administration of hCG was determined. One group of adult male monkeys was treated with a low dose (5-10 micrograms/day) and a second group with a high dose (25 micrograms/day) of a GnRH agonist for 44 weeks. Basal and peak testosterone concentrations were both significantly reduced by GnRH agonist treatment in all groups compared to untreated control animals, but the % rise in serum testosterone above basal values in response to hCG administration was unchanged by agonist treatment. In Exp. 2, the GnRH agonist (100 or 400 ng) or a GnRH antagonist (4 micrograms) was infused into the testicular arteries of adult monkeys. The agonist did not alter testosterone concentrations in the testicular vein or testosterone and LH values in the femoral vein. In Exp. 3, testicular interstitial cells from monkeys were incubated with three concentrations (10(-9), 10(-7) and 10(-5)M) of the GnRH agonist or a GnRH antagonist with and without hCG. After 24 h, neither basal nor hCG-stimulated testosterone production was affected by the presence of the GnRH agonist or antagonist. The results from all 3 experiments clearly suggest that GnRH agonist treatment does not directly alter steroid production by the monkey testis.     

Serum testosterone concentration in response to exogenous GnRH does not predict service rates or pregnancy rates by yearling, performance tested, crossbred bulls

Ten bulls with a scrotal circumference of less than 30 cm at the end of growth performance testing, and 10 cohorts of the same age, size and breed type with a scrotal circumference greater than 30 cm were used to evaluate if testosterone response following GnRH administration could be used to test for fertility, for semen quality, and for specific pathologic testicular parenchymal changes. Serum testosterone concentrations were determined immediately before and 2 to 3 hours following intramuscular injection of 250 ug GnRH. Bulls were examined for breeding soundness, then fertility was tested in a breeding trial; testicular histology was assessed by determining the percentage of cross-sections of seminiferous tubules with no spermatocytes. The mean (+/- SEM) post-GnRH serum testosterone concentration for all bulls was 11.71 (+/-0.64) ng/ml. In order to examine for an association, the GnRH response was classified as above or below the mean for resultant serum testosterone concentration. The GnRH response classification was not related to the scrotal circumference, percentage of tubules devoid of spermatocytes, or percentage of progressively motile spermatozoa (P > 0.10). The percentage of morphologically normal spermatozoa was significantly higher (P < 0.05) in the bulls with a higher than mean testosterone secretion in response to GnRH injection. In the breeding trial, the percentage of heifers bred and the percentage of heifers pregnant (60 days post breeding) were not significantly different (P > 0.10) between the 2 classifications of GnRH response. The GnRH response test was related to the percentage of morphologically normal spermatozoa but did not predict fertility of yearling bulls in this study.     

Seasonal variation in serum testosterone, testicular volume and semen characteristics in coatis (Nasua nasua)

The objective was to characterize seasonal changes in serum testosterone concentration, testicular volume and sperm quantity and quality in captive coatis (Nasua nasua) from Pantanal, MT, Brazil. Sampling was done once monthly for 1 y. Mean (± SEM) serum testosterone concentrations (767.37 ± 216.2 ng/ml) and total and progressive sperm motility (79.6 ± 3.9%; 3.8 ± 0.3, on a scale of 0 to 5) peaked in July. The highest combined testis volume (10.3 ± 0.4 cm³) and sperm concentration (403 million ± 102 sperm/ml) occurred in August, at the peak of the winter breeding season. No seasonal effects on percentages of morphologically normal sperm, acrosome integrity, or live sperm were detected; however, the percentage of secondary sperm defects was higher in the winter. In conclusion, intricate relationships between testosterone concentration, testis volume, semen concentration and total and progressive sperm motility with high levels of breeding activity were observed during the dry season in the winter (June, July, August), followed by a subsequent decline in these activities during the wet season (i.e., summer: December, January, February). There was no seasonal pattern for production of functionally intact and morphologically normal sperm.     

Effect of age,pubertal stage and season on testosterone concentration in male dromedary camel

The present study was conducted in the Laboratory of Animal Physiology and Biotechnology, Department of Animal Production, Faculty of Agriculture, Mansoura University, Egypt. The present investigation aimed at studying effects of ages, pubertal stages and seasons of the year on testosterone concentrations in blood plasma and tissue homogenate of the testes. The testes used in the current study were collected from a total of 104 one-humped male camels (Camelus dromedarius). Samples were taken from pre (1–3.5 years) and post (3.5–13 years) pubertal camels. Testes were studied for a two consecutive seasons. The freshly prepared homogenate of the testicular tissue and blood plasma were used for determining the concentrations of testosterone in plasma and testicular extract. The concentrations of testosterone in blood plasma and testicular tissue were significantly increased during the breeding season compared with that of non-breeding season; the concentration of testosterone was higher in testicular tissue than in blood plasma.Testosterone concentrations in plasma and testicular tissue were increased in breeding than in non-breeding season. In addition, the testosterone concentrations were closely related with seasonal changes, stage of puberty and advancing age.     

Variation in sexual behaviors in a group of captive male Yangtze finless porpoises (Neophocaena phocaenoides asiaeorientalis): motivated by physiological changes?

Most male mammals in temperate regions demonstrate seasonal sexual behaviors that coincide with seasonal variations in gonadal activities and androgen hormones. The Yangtze finless porpoise is a temperate freshwater cetacean species and an obvious seasonal breeder. To investigate the relationship between sexual behavior and gonadal activity in this animal, testicular size (volume) and structure (ultrasonogram pixel intensity) of two adult male porpoises (AF, AB) and one sub-adult male (TT) were longitudinally monitored from November 2008 to November 2009. Serum testosterone concentration was also monitored during the same period. Variations in the frequency of sexual behavior in AF and AB had similar, but seasonal trends. Their testicular size and pixel intensity also varied seasonally. Testicular size increased in March, peaked from April through June, and decreased gradually from August through September, whereas testicular pixel intensity started to increase in early February. The frequency of sexual behavior was positively correlated with testicular volume and pixel intensity (P = 0.000018 and P = 0.00012, respectively) in AF. Serum testosterone concentrations also varied. The sub-adult male porpoise, TT, was undergoing puberty, as evidenced by its marked increase in testicular volume, testicular pixel intensity, and serum testosterone concentrations from the beginning of 2009. Interestingly, TT exhibited the highest frequency of sexual behavior, most of which was same-sex pairing. However, its oversexed behavior neither quantitatively correlated with its smaller testicular volume (P = 0.61) nor with its testicular pixel intensity (P = 0.69).     

Effect of injection of gonadotrophin-releasing hormone on testicular steroidogenesis in the hypogonadal (hpg) mouse

Hypogonadal (hpg) mice were injected once daily with 10 ng, 50 ng or 1 microgram GnRH for 5, 10 or 20 days or 12 times daily with 4.2 ng GnRH for 5 days. Basal and hCG-stimulated production in vitro of androstenedione, testosterone and 5 alpha-androstane-3 alpha,17 beta-diol (androstanediol) were measured by radioimmunoassay. All doses of GnRH increased testicular weight and in-vitro androgen production although seminal vesicle weights were unchanged and serum testosterone concentrations remained undetectable. After 5 days' treatment androstenedione and androstanediol were the dominant androgens produced, the latter indicating the presence of high levels of 5 alpha-reductase. By 20 days testosterone production was predominant after treatment with higher doses of GnRH. Total androgen production (androstenedione + testosterone + androstanediol) after 5 and 10 days was similar at all concentrations of GnRH used. After 20 days' treatment total androgen production was significantly greater with 50 ng GnRH/day than with 10 or 1000 ng/day. Multiple daily injections of 4.2 ng GnRH (total dose 50 ng/day) had no greater effect on androgen production in vitro compared to single daily injections of 50 ng. This suggests that under the conditions used in this study the testis does not require pulsatile release of the gonadotrophins. The pattern of [3H]pregnenolone metabolism was measured after 5 days injection of 50 ng GnRH/day. Compared to control hpg animals there was a significant increase in formation of C19 steroids, synthesis being solely through the 4-ene pathway. These results show that GnRH treatment of hpg mice will induce testicular steroidogenesis.(ABSTRACT TRUNCATED AT 250 WORDS)     

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)     

Active immunization against gonadotrophin-releasing hormone in Chinese male pigs: effects of dose on antibody titer, hormone levels and sexual development

The objective of this study was to determine the optimal dose of a GnRH vaccine for immunocastration of Chinese male pigs, based on immune, endocrine and testicular responses. Forty-two crossbred (Chinese Yanan x Large White) male pigs were randomly assigned to one of the five treatments as follows: (I) 0 microg (control, n=8); (II) 10 microg (n=8); (III) 62.5 microg (n=8); (IV) 125 microg (n=8); (V) 250 microg (n=10), D-Lys6-GnRH tandem dimer (TDK) peptide equivalent of conjugate (TDK-OVA), using Specol as the adjuvant. Pigs were immunized at 13 and 21 weeks of age and were slaughtered at 31 weeks of age. Blood samples for antibody titer and hormone assays were collected at 13, 21, 24 and 31 weeks of age. At these time-points, testis size was also measured. At slaughter, testis weight was recorded and fat samples were collected for androstenone assay. Four animals, one out of each immunized group, responded poorly to the immunization (non-responders). At slaughter, serum testosterone and LH levels, fat androstenone levels and testis size/weight of these non-responders were similar to those in control animals. Antibody titers of non-responders were substantially lower (P<0.05) than in other immunized pigs. For the animals that responded well to the immunization (immunocastrated pigs), serum testosterone and LH levels, fat androstenone levels and testis size or weight were reduced (P<0.05) as compared to either controls or non-responders, at all doses tested. There was a significant effect of dose of TDK-OVA on antibody titers. The overall mean antibody titers in the 62.5 or 125 microg dose group (53.6 and 50.5% binding, respectively) were significantly higher than in the 10 or 250 microg group (39.2 and 40.24% binding, respectively). At slaughter, there was a significant dose effect on testis size or weight and on serum testosterone levels, but there was no dose effect on serum LH levels and fat androstenone levels. Testis size or weight in the 10 microg group was reduced to a lesser extent (P<0.05) than in the three higher dose groups. At slaughter, in comparison to controls, mean testis size of immunocastrated pigs in treatments II-V was reduced to 55, 21, 33 and 25%, respectively, whereas testis weight was reduced to 39, 12, 18 and 14%, respectively. Reduction of testis size and/or weight is important for visual assessment of castration at the slaughterline, therefore, it is concluded that a dose of 10 microg peptide is not suitable. We conclude that, within the dose-range studied, the 62.5 microg dose is optimal for future GnRH immunization studies or future practical use in immunocastration of Chinese male pigs.     

Active immunization against GnRH in pre-pubertal domestic mammals: testicular morphometry,histopathology and endocrine responses in rabbits,guinea pigs and ram lambs

Effective tools for male contraception are important in the control of reproduction in animal populations. The aim of the present study was to evaluate the effects of active immunization against gonadotropin-releasing hormone (GnRH) on male reproductive function assessing testicular morphological changes and serum-gonadotropin levels in pre-pubertal rabbits, guinea pigs and ram lambs. An anti-GnRH vaccine was developed by linking a GnRH-homologous molecule to a tetanus clostridial toxoid (Al(OH)₃ coadjuvant). After vaccination protocols testicular morphometry, histopathological alterations and endocrine responses (FSH, LH, testosterone and cortisol serum levels) were evaluated. Testicular volume was significantly reduced in vaccinated animals with respect to the control group in rabbits, guinea pigs and ram lambs (P<0.05 to P<0.001). The anti-GnRH vaccine generated a reduction in testicular volume of 15-, 27- and 11-fold, respectively. Tubule diameters decreased in the vaccinated group with respect to the control ~2.0-, 1.2- and 3.5-fold, respectively (P<0.001). Tubule, intertubular and lumen volumes significantly decreased in vaccinated rabbits (P<0.05), guinea pigs and ram lambs (P<0.01). Vaccinated animals of the three species showed significant reductions in spermatogonial numbers (10- to 40-fold; P<0.01). Sperm was absent in all seminiferous tubules of all rabbits, and most individuals of guinea pigs (80%) and ram lambs (60%). No significant differences were observed between vaccinated and control groups regarding FSH and LH during the experiments in the three experimental species/models used. Testosterone, however, was only significantly lower (~22-fold, P<0.01) in vaccinated rabbits. In conclusion, the present study demonstrated that pre-pubertal active immunization against GnRH leads to endocrine disruption and marked differences on testicular morphometry, development and activity among lagomorphs, hystricomorphs and ovine species with species-specific sensitivity regarding the anti-GnRH immune response.     

Testosterone secretion in young and adult buffalo bulls

Studies were conducted to determine the 24-hour fluctuations in blood serum testosterone concentration in adult buffalo bulls, and to measure testosterone secretion before and after GnRH administration in male buffaloes of different age groups. Testosterone levels in three sexually mature bulls ranged from 0.2 to 2.7 ng/ml with a mean of 0.6 +/- 0.2 ng/ml. Samples collected in November had significantly higher (P<0.05) testosterone than those drawn in February (dry season) as did samples collected during the day as opposed to the night. Sera testosterone concentrations were lower in younger bulls with a range of 0.2 to 0.6 ng/ml. GnRH induced an increase in testosterone in 6, 12, 24 and 36-month old bulls with the greatest response being observed at 36 months. GnRH did not elicit a response in one-month old bulls. It may be concluded that baseline sera testosterone concentrations in buffalo bulls, as well as responsiveness to GnRH injection, increase with sexual maturity and are subject toseasonal and diurnal variations.     

Testosterone selectively increases serum follicle-stimulating hormonal (FSH) but not luteinizing hormone (LH) in gonadotropin-releasing hormone antagonist-treated male rats: evidence for differential regulation of LH and FSH secretion

Both testosterone (T) and gonadotropin-releasing hormone (GnRH)-antagonist (GnRH-A) when given alone lower serum luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in intact and castrated rats. However, when graded doses of testosterone enanthate (T.E.) were given to GnRH-A-treated intact male rats, a paradoxical dose-dependent increase in serum FSH occurred; whereas serum LH remained suppressed. This surprising finding led us to ask whether the paradoxical increase in serum FSH in GnRH-A-suppressed animals was a direct stimulatory effect of T on the hypothalamic-pituitary axis or the result of a T effect on a testicular regulator of FSH. To test these hypotheses, we treated adult male castrated rats with GnRH-A and graded doses of T.E. In both intact and castrated rats, serum LH remained undetectable in GnRH-A-treated rats with or without T.E. However, addition of T.E. to GnRH-A led to a dose-dependent increase in serum FSH in castrated animals as well, thus pointing against mediation by a selective testicular regulator of FSH. These data provide evidence that pituitary LH and FSH responses may be differentially regulated under certain conditions. When the action of GnRH is blocked (such as in GnRH-A-treated animals), T directly and selectively increases pituitary FSH secretion.     

Effect of casein diet on gonadotropin releasing hormone antagonist induced changes in adrenal gonadal functions in male rats

Adult male rats received daily injections (sc) of gonadotropin releasing hormone antagonist (0.2 mg/kg(-1) x day(-1)) for 21 days when they were sacrificed on day 22, adrenal weight, adrenal A5-3beta (delta 5-3beta) hydroxysteroid dehydrogenase (Delta5-3beta-HSD) activity and serum level of corticosterone were increased significantly while testicular 17beta (17beta) hydroxysteroid dehydrogenase (17beta-HSD) activity and serum level of testosterone and spermatogenesis were decreased in the rats fed on 5% casein diet. GnRH antagonist treated rats fed on 20% casein diet, resulted significant decrease in adrenal weight, serum corticosterone and adrenal A5-3beta-HSD activity while testicular 17beta-HSD activity serum testosterone levels and the weights of sex organs were increased with respect to anti GnRH treated rats fed on 5% casein diet. But the GnRH antagonist treated rats fed on 20% casein diet showed decreased spermatogenesis quantitatively and sperm count appeared similar to anti GnRH treated rats fed on 5% casein diet. These results indicate that high casein diet protects adrenocortical activity and stimulates testosterone synthesis without effecting spermatogenic arrest in GnRH antagonist treated rats. It may be concluded that GnRH antagonist in presence of high milk protein diet may be considered to be a suitable antihormone in the development of an ideal male contraceptive.     

L'andropause

In men, aging is associated with progressive impairment of testicular function. Decrease in total testosterone levels with aging has been reported in many studies in normal healthy men. This decrease has a primarily testicular origin, as shown by decreased number of Leydig cells in histological studies, increased basal gonadotropin levels and decreased response to hCG. A greater decrease in bioavailable testosterone rather in than total testosterone concentrations is explained by the age-dependent increase in the SHBG concentration. Although immunoreactive gonadotropin levels are higher than in young men, a relative alteration of bioactive gonadotropin secretion by the pituitatry occurs in ederly men. Althought the definitive demonstration of an alteration of GnRH secretion by the hypothalamus cannot be established in healthy ederly men, such an alteration might be responsible for a decompensation of the testicular function in case of intercurrent illness. Increased FSH and decreased inhibin plasma levels are indicating a similar alteration in seminiferous tubules as directly demonstrated by histological data showing a decrease of Sertoli cell number and daily sperm production with aging. Although the incidence of sexual dysfunction increases with aging, the relationship between sexual behaviour and testicular endocrine function remained a mater of controversy. A threshold of testosterone action on sexual behavior might be responsible for the difficulty in establishing this relationship. Although some controled studies are available, the risk-to-benefit balance of androgen substitution in older male remained a controversial issue. A positive effect on sense of well-being and/or libido has been and the lack of adverse effect on lipid and carbohydrate metabolism had been demonstrated in short term studies, however, the role of androgens in the benign hypertrophy of the prostate and in stimulating the growth of latent prostate adenocarcinoma remained to be more clearly established by longterm controlled studies.     

Active immunization of boars against gonadotrop in releasing hormone. I. Effects on reproductive parameters

Sexually mature boars were actively immunized against gonadotropin releasing hormone (GnRH) to characterize endocrine and gametogenic changes associated with immunoneutralization of endogenous GnRH. Injections of GnRH conjugated to bovine serum albumin (BSA) given five times over 24 wk induced production of antibodies against GnRH in all animals (n = 5). Active immunization against GnRH reduced serum concentrations of testosterone (P < 0.05) and luteinizing hormone (LH) (P < 0.05), testes volume (P < 0.01), paired testis weights (P < 0.05), paired epididymis weights (P < 0.05), sperm per testis (P < 0.01) and seminiferous tubule diameters (P < 0.001) when compared with controls (n = 4). These results indicate that both steroidogenic and spermatogenic functions are impaired in testes of mature boars actively immunized against GnRH.     

Chronic treatment of male tammar wallabies with deslorelin implants during pouch life: effects on development, puberty, and reproduction in adulthood

The present study evaluated the effects of chronic GnRH agonist (deslorelin) treatment on sexual maturation in the male tammar wallaby. Slow-release deslorelin or placebo implants were administered to male pouch young (n = 10/group) when they were between 180 and 200 days old, to determine if disruption of the pituitary-testicular axis during development altered the timing of sexual maturation or had long-term effects on adult reproductive function. Deslorelin treatment caused retardation of testicular growth and reduced the serum FSH and testosterone concentrations between 12 and 24 mo of age. Maturation of the hypothalamic-pituitary-testicular axis was also delayed in treated animals at 13 and 19 mo of age. Despite these alterations in the pattern and timing of neuroendocrine development, sexual maturation was not permanently blocked in these animals and deslorelin-treated animals reached sexual maturity at the same age as treated animals, as evidenced by a fully functional pituitary-testicular axis and proven fertility at 25 mo of age. The ability of the treated animals to reach puberty at the same time as control animals, despite delayed maturation of the hypothalamic-pituitary-testicular axis, suggests that puberty in the male tammar wallaby is additionally regulated by other, gonadotropin-independent factors.