Bilateral enucleation and captivity influence the reproductive cycle of male Viscacha (Lagostomus maximus maximus)

The viscacha (Lagostomus maximus maximus) is a seasonal rodent living in the Southern Hemisphere. The adult males exhibit an annual reproductive cycle characterized by a gonadal regression period during winter. In this study, we investigated the effects of bilateral enucleation and captivity on their annual reproductive cycle. Testicular volume relative to body weight was recorded monthly in intact and bilaterally enucleated animals placed under natural photoperiod, water, and food ad lib. and constant temperature. Testes and accessory organs were evaluated by qualitative and quantitative light microscopic studies. The intact animals showed an annual reproductive cycle with complete gonadal atrophy in the first year. In the second year, testicular regression was observed but attenuated in regard to that recorded in the first winter period, indicating that adaptive changes might be involved. Bilateral enucleation in the viscacha dampened and extended the period of its annual reproductive cycle. The results suggest that both conditions, constant captivity and enucleation, produced stimulatory effects on the reproductive system of this rodent. Furthermore, local control mechanisms might be responsible for the morphological differences observed in testes, epididymis, and seminal vesicles from both groups, which exhibited similar levels of serum testosterone. Finally, an intact retinohypothalamic-pineal axis and/or photoperiodic input would be necessary to maintain the reproductive cycle amplitude and timing in viscacha.     

Noninvasive assessment of seasonal hormone profile in captive bald eagles (Haliaeetus leucocephalus)

The hypothesis was to test whether a ratio of estrogen:androgen in eagle feces would reflect gonadal activity, and whether our procedure for noninvasive hormone analysis of fecal steroids could be applied to assess seasonal reproductive function in four captive bald eagles (Haliaeetus leucocephalus). Total immunoreactive excretory estrogens (E) and testosterone (T) were analyzed and compared as an E/T ratio from ad libitum monthly stool collections during the 1980–81 breeding season of birds maintained in an artificial insemination (AI) project. Since active male gonads are known to secrete a preponderance of androgens into the peripheral circulation and that renal clearance filters steroid metabolites into the urine, it was reasonable to assume that a lowered excretory E/T profile would mimic major changes in male seasonal steroidogenesis; analogously, active female gonads would result in an increased excretion of urinary estrogens, in turn reflected by a seasonal elevation of E/T ratios. A serial profile of excretory E/T ratio data for two male bald eagles approximated unity values except for a midseason low (x < 0.4) in February, one month prior to semen collections, followed by a significant end-of-breeding season rise in E/T values (x > 2.5, P < 0.01). The average E/T profile from data of two female eagles were two- to sixfold higher than males except for a significant mid-breeding season peak in E/T values during March (x > 13.5, P < 0.01). Despite the absence of nest building or egg production by either female, these preliminary observational data indicated seasonal patterns of gonadal activity in both female eagles that were synchronous with semen availability from adjacent males.     

Seasonal changes in inhibin activity in seminal plasma and serum concentrations of FSH, LH and testosterone in the male goat (Capra hircus)

Inhibin activity in goat seminal plasma was measured by in vitro assay throughout successive 9 months and its relationship with the serum FSH, LH and testosterone concentrations was investigated. Total inhibin activity (TIA) in seminal plasma gradually increased from spring to summer, reduced in autumn (P<0.05) and recovered toward winter (P<0.05). Serum FSH and LH reached a peak in mid-summer (P<0.01) and returned to the low levels in autumn. Serum testosterone also increased in mid-summer and kept the high levels until the early winter (P<0.05). Some positive correlation was found in monthly levels between seminal TIA and serum FSH (r=0.305; P<0.05). Results suggest that the summer increase of inhibin activity in seminal plasma relates with the mid-summer rise of serum FSH levels in the male goat.     

The natural plasma testosterone profile of male blue tits during the breeding season and its relation to song output

In male birds, the gonadal hormone testosterone (T) is known to influence territorial and mating behaviour. Plasma levels of T show seasonal fluctuations which vary in relation to mating system and social instability. First, we determined the natural T profile of male blue tits Parus caeruleus during the breeding season. We found that plasma levels of T increased at the onset of nest building. Thus, the increase in circulating T was not associated with territory establishment, nor with the fertile period of the males' mates. In most individuals, T levels dropped to values close to zero during the period of chick feeding. Second, we investigated the relationship between plasma levels of T and male age, size, and singing behaviour. During the mating period, T levels did not differ between 1 yr old and older males and did not correlate with body size or condition. However, song output during the dawn chorus tended to be positively correlated with T levels. Therefore, if high T levels are costly, song output might be an honest indicator of male quality in blue tits. Finally, we show that plasma levels of T are significantly higher during the night than during the day. This pattern has also been observed in captive non-passerine birds, but its functional significance remains unknown.     

Testosterone undecanoate in the functional compartments of the male reproductive tract

Background

Assessment of testosterone undecanoate’s (TU) presence in the functional compartments of the male reproductive tract has never been performed despite the evidence that its documented beneficial effect in male infertility might be mediated through an epididymal action and this study was set to examine this possibility.

Materials and methods

In 18 normozoospermic volunteers TU has been administered (40 mg t.i.d.) for 6 days with serum measurements of TU, total testosterone (T), DHT, E2, SHBG, FSH, LH, and PRL before and at the end of medication. Steroid hormones (T, E2, and TU) were also assayed in seminal plasma. In a selected group of 7 men with previously diagnosed non-obstructive azoospermia TU, T, and E2 were assayed in the extracts of testicular biopsy material taken before ICSI and at the end of the same medication.

Results

A marked rise of serum DHT (average 148%, P < 0.001) has been found after treatment, whereas T, E2, FSH, LH, SHBG, and PRL did not significantly change. Measurable amounts of TU were found in the serum of all men but only in 6 cases in seminal plasma (11.1 ± 8.0 ng/mL) and all of them in semen delivered 7–8 h after the last TU capsule was taken. In dilution fluid from testicular tissue extracts, no detectable amounts of TU were found whereas mean values of 92.5 ± 54.3 pg/mL and 43.8 ± 16.3 ng/mL for E2 and T were observed. Positive correlations among TU and E2, T or DHT concentrations were found in serum samples (P < 0.01, 0.02, and 0.002) as well as between E2 and T (P < 0.01), E2 and DHT (P < 0.001), or T and DHT (P < 0.001).

Conclusion

It is concluded that TU was identified and measured for the first time in seminal plasma of a fair percentage (33%) of men on this medication and was associated in all men with a marked rise of DHT concentration, a known epididymal function promoter, in the absence of an effect on pituitary and gonadal activity. On this evidence, it appears that a beneficial effect of TU on epididymal function may be a distinct possibility.     

Testosterone prevents but not reverses anhedonia in middle-aged males and lacks an effect on stress vulnerability in young adults

Middle-aged male rats are more vulnerable than young adult ones to develop anhedonia when exposed to chronic mild stress (CMS). Clinical studies support the idea that in aged subjects the low testosterone (T) levels are related with their higher stress vulnerability and that this hormone possesses antidepressant-like actions. In this study we evaluated the role of gonadal hormones--mainly T--on the depressive-like behavior of middle-aged and young adult male rats submitted to CMS. In middle-aged rats we analyzed the effect of T restitution (at the levels of young adult animals) given 3 weeks before (experiment 1) or 3 weeks after (experiment 2) anhedonia development (indicated by a reduction in sucrose solution intake). T restitution before CMS effectively prevented anhedonia but failed to reverse it once installed. In young adult rats we studied if orchidectomy increased stress vulnerability and found that it failed to modify sucrose intake. These results indicate a stress-dependent differential effect of T in middle-aged rats an age differential role of gonadal hormones on the vulnerability to develop anhedonia. The results suggest that T is a resilience factor in middle-aged but not in young adult males.     

Transgenic models to study gonadotropin function: the role of follicle-stimulating hormone in gonadal growth and tumorigenesis.

The role of FSH in gonadal tumorigenesis and, in particular, in human ovarian cancer has been debated. It is also unclear what role the elevated FSH levels in the inhibin-deficient mouse play in the gonadal tumorigenesis. To directly assess the role of FSH in gonadal growth, differentiation, and gonadal tumorigenesis, we have generated both gain-of-function and loss-of-function transgenic mutant mice. In the gain-of-function model, we have generated transgenic mice that ectopically overexpress human FSH from multiple tissues using a mouse metallothionein-1 promoter, achieving levels far exceeding those seen in postmenopausal women. Male transgenic mice are infertile despite normal testicular development and demonstrate enlarged seminal vesicles secondary to elevated serum testosterone levels. Female transgenic mice develop highly hemorrhagic and cystic ovaries, have elevated serum estradiol and progesterone levels, and are infertile, mimicking the features of human ovarian hyperstimulation and polycystic ovarian syndromes. Furthermore, the female transgenic mice develop enlarged and cystic kidneys and die between 6-13 weeks as a result of urinary bladder obstruction. In a complementary loss-of-function approach, we have generated double-homozygous mutant mice that lack both inhibin and FSH by a genetic intercross. In contrast to male mice lacking inhibin alone, 95% of which die of a cancer cachexia-like syndrome by 12 weeks of age, only 30% of the double-mutant male mice lacking both FSH and inhibin die by 1 yr of age. The remaining double-mutant male mice develop slow-growing and less hemorrhagic testicular tumors, which are noted after 12 weeks of age, and have minimal cachexia. Similarly, the double-mutant female mice develop slow-growing, less hemorrhagic ovarian tumors, and 70% of these mice live beyond 17 weeks. The double-mutant mice demonstrate minimal cachexia in contrast to female mice lacking only inhibin, which develop highly hemorrhagic ovarian tumors, leading to cachexia and death by 17 weeks of age in 95% of the cases. The milder cachexia-like symptoms of the inhibin and FSH double-mutant mice are correlated with low levels of serum estradiol and activin A and reduced levels of aromatase mRNA in the gonadal tumors. Based on these and our previous genetic analyses, we conclude that elevated FSH levels do not directly cause gonadal tumors. However, these results suggest FSH is an important trophic modifier factor for gonadal tumorigenesis in inhibin-deficient mice.     

Fenugreek potent activity against nitrate-induced diabetes in young and adult male rats

Nitrate has described as an endocrine disruptor that promotes onset of diabetes. This study was undertaken to evaluate diabetic effect of high nitrate intake in young and adult male rats and its amelioration by fenugreek administration. The study revealed significant increase in serum glucose and blood glycosylated hemoglobin (HbA1c%), while serum insulin and liver glycogen were decreased among nitrate exposed animals, in particular the young group. A significant reduction in the body weight gain and serum thyroid hormones (T4 & T3) was also recorded. Further reduction in serum levels of urea and creatinine, as well as total protein in serum, liver and pancreas was demonstrated, with elevation in their levels in the urine of all nitrate exposed groups. Meanwhile, the activity of serum transaminases (ALT and AST) was increased, with decline in their activity in the liver tissue. In addition, an elevation in serum total bilirubin, tissues (liver and pancreas) nitric oxide and lipid profile, as well as liver activity of glucose-6-phosphatase was recorded. Fenugreek administration to nitrate exposed rats was found to be effective in alleviating hyperglycemia and other biochemical changes characterizing nitrate-induced diabetes. So, fenugreek can be considered to possess potent activity against onset of nitrate induced-diabetes.     

Immunomodulatory cytokines in human seminal plasma correlate with immunomodulatory steroids

7alpha-Hydroxy-dehydroepiandrosterone and its 7beta-hydroxyepimer, which act as local immunomodulatory agents, dehydroepiandrosterone, cortisol, and major androgens, together with four cytokines-interleukins 2, 4, 10, and IFN-gamma, reflecting the activity of TH1 or TH2 cells present in semen, were measured in seminal plasma from 35 male donors. Cortisol, dehydroepiandrosterone, its sulfate, 7-hydroxy-dehydroepiandrosterone epimers, testosterone, and estradiol were also measured in their blood serum. Steroids and interleukins in semen as well as serum steroids and seminal interleukins were mutually correlated to find out whether a relationship between immunomodulatory steroids and cytokines influencing the immune environment does exist. A highly significant (P<0.001) positive correlation was found between seminal 7beta-hydroxy-dehydroepiandrosterone and IFN-gamma, while a negative correlation was found between cortisol and IL-10. Highly significant positive correlations were also found between serum 7alpha-hydroxy-dehydroepiandrosterone and seminal IFN-gamma and between serum 7beta-hydroxy-dehydroepiandrosterone and seminal IL-2, while a negative correlation was found between serum dehydroepiandrosterone and seminal IL-10. Different and in some instances, even contradictory findings concerning the influence of dehydroepiandrosterone and cortisol on TH1 and TH2 cytokines were observed in seminal plasma as compared to those found by others in serum. The differences can be ascribed to the different environments of mucosal and systemic immunity. Correlations between the levels of steroids and cytokines in seminal plasma did not always correspond to the correlations between given cytokines and hormones in sera. The results, however, are in agreement with our recent finding of an autonomous production of these steroids in the male reproductive tract.     

Effects of cocaine hydrochloride on the male reproductive system

The reproductive system effects of cocaine were studied in male rats. The analysis included measurements of circulating levels of luteinizing hormone (LH) and testosterone (T) by radioimmunoassay (RIA). The weights of the testes and sex accessory organs were also assessed and compared with control animals. Dosage level, duration of treatment, and interval between injection and sacrifice were the parameters examined. Following a single intraperitoneal (IP) injection, LH levels decreased over a 3-hour period. At a high dosage (40 mg/kg), cocaine caused a significant elevation in serum T followed by a significant depression of T for at least 2 hours. When administered chronically for 15 days, the low dose group (10 mg/kg) did not vary significantly from the vehicle controls. However, the high dose group had lower LH and T levels, as well as correspondingly lighter weight seminal vesicles and epididymis. No changes were noted in the weights of the ventral prostate or testes. This research suggests that cocaine acts primarily at the hypothalamic-hypophyseal axis with a possible secondary action at the gonadal level.     

Underlying physiological control of reproduction in urban and forest-dwelling European blackbirds Turdus merula

The development and the continual expansion of urban areas have not only destroyed natural habitats, but also have drastically changed the environmental and ecological conditions of these areas. Consequently, species that have settled in these new man-made ecosystems are exposed to considerable alternations in environmental conditions compared to their 'wild' conspecifics. To understand the impact of human-induced environmental changes on life history events such as reproduction, we compared the timing of the reproductive season and its underlying endocrine control in free-living European blackbirds Turdus merula inhabiting urban and nearby forest areas. Body mass, fat score, gonadal size, luteinizing hormone (LH), testosterone (T), and estradiol (E₂) were measured. Urban blackbirds developed their gonads approximately three weeks earlier than forest birds, whereas the timing of gonadal regression did not differ. There are several factors (e.g. artificial light, temperature, food availability, and social cues) which may have caused the differences in the temporal organization of gonadal growth between the urban and forest-living populations. The advanced gonadal development of urban blackbirds did not coincide with an earlier secretion of reproductive hormones. In contrast, urban males had lower plasma LH and T levels during testicular growth than forest males. Differences in social interactions and environmental conditions may explain the contrast of gonadal development and the timing of hormone secretion between urban and forest blackbirds.     

Tissue damage in the male murine reproductive system during experimental Taenia crassiceps cysticercosis

Chronic infection with Taenia crassiceps cysticerci in male mice increases the level of estradiol in serum, whereas it reduces that of testosterone. In addition, male mice lose their typical male reproductive behavior. The effects of cysticerci infection on the histomorphology of male reproductive tissues are unknown. The present study was undertaken to determine the histological changes in testes, seminal vesicles, and prostate of male mice infected with T. crassiceps cysticerci. At 16 wk of infection, all tissues exhibited high inflammatory infiltrate. Tissue lesions included marked dilation and peripheral fibrosis. In the testes, a diminution of spermiogenesis was observed. The overall results indicated that the histological changes in chronically parasitized male mice occurred with changes in hormone levels, simultaneously with the high inflammatory immune response.     

Androgen receptors are required for full masculinization of nitric oxide synthase system in rat limbic-hypothalamic region

The neuronal nitric oxide synthase (nNOS) is involved in the control of male and female sexual behavior and its distribution in several regions of the limbic–hypothalamic system, as well as its coexistence with gonadal hormones' receptors, suggests that these hormones may play a significant role in controlling its expression. However, data illustrating the role of gonadal hormones in controlling the nNOS expression are, at present, contradictory, even if they strongly suggest an involvement of testosterone (T) in the regulation of nNOS. The action of T may be mediated through androgen (AR) or, after aromatization to estradiol (E₂), through estrogen receptors.To elucidate the role of AR on nNOS expression, we compared male and female rats with a non-functional mutation of AR (Tfm, testicular feminization mutation) to their control littermates. We investigated some hypothalamic and limbic nuclei involved in the control of sexual behavior [medial preoptic area (MPA), paraventricular (PVN), arcuate (ARC), ventromedial (VMH) and stria terminalis (BST) nuclei]. In BST (posterior subdivision), VMH (ventral subdivision), and MPA we detected a significant sexual dimorphism in control animals and a decrease of nNOS positive elements in Tfm males compared to their littermate. In addition, we observed a significant increase of nNOS positive elements in BST (posterior) of Tfm females. No significant changes were observed in the other nuclei. These data indicate that, contrary to current opinions, androgens, through the action of AR may have a relevant role in the organization and modulation of the nNOS hypothalamic system.     

METHYLTESTOSTERONE-INDUCED DIFFERENTIATION OF A SEMINAL VESICLE HOMOLOGUE IN JUVENILE GOLDFISH, CARASSIUS AURATUS L.

In male goldfish, a structure homologous to the seminal vesicles of other fishes develops from the posterior sterile region of testicular ridges coincidentally with the initiation of spermatogenesis in the anterior region. Sexually differentiated juvenile goldfish were administered with methyltestosterone (50 μg/g diet) for a period of 20 days from 40 (experiment I) and 60 days (experiment II) after hatching. In both experiments, androgen administration exerted inhibitory influences on germ cell development in both sexes, but rather promoted the formation of the ovarian lumen, and of its residues in male gonads as well, accompanied with columnar hypertrophy and ciliation of the epithelium. The same treatment brought about a prominent development of the seminal vesicle homologues in the caudalmost gonadal ridges of females as well as in those of males in experiment II but not in experiment I. The cause of difference in the effects between the two experiments seemed to be ascribable to an incomplete prolongation of the gonadal ridges up to the presumptive area of the organ at the start of experiment I. Thus the capacity of the seminal vesicle primordia, common to both sexes, to make their due differentiation in response to exogenous androgen is confirmed in this study.     

Geographical and taxonomic variation in the pattern of natural sex reversal in the teleost fish order Synbranchiformes

Two types of males have been found in all members of the Synbranchidae. The primary males are born as males and possess single, but bilobular, testes with two gonadal sinuses. Secondary males evolve by sex reversal of functional females and possess a lamellar organization of the testes with three gonadal sinuses and often ovarian residua. Undifferentiated races lack primary males and are recorded only from certain geographical areas. Rudimentary hermaphroditism is classified as a derived evolutionary stage and gonochorism, which is represented in the Amphipnoidae, a primitive evolutionary condition. The alternative of primary versus secondary male is decided by a genetic shift mechanism instead of by environmental conditions. The precarious poise of sexual identity in the Synbranchidae is defined as a switch mechanism to compensate for the vicissitudes of the natural habitat, allowing reproduction in spite of severe population depletions. Based on an examination of its gonadal structure, Alabes is considered to have no phylogenetic affinities with the Synbranchiformes. The occurrence of natural hermaphroditism in phylogenetically unrelated groups of fishes in radically different environments is regarded as the results of chance evolution, rather than convergence.     

Gonadal restructuring and correlative steroid hormone profiles during natural sex change in protogynous honeycomb grouper (Epinephelus merra)

The honeycomb grouper shows protogynous hermaphroditism. The endocrine mechanisms involved in gonadal restructuring throughout protogynous sex change are largely unknown. In the present study, we investigated changes in the gonadal structures and levels of serum sex steroid hormones during female to male sex change in the honeycomb grouper. On the basis of histological changes, entire process of sex change was assigned into four developmental phases: female, early transition (ET), late transition (LT), and male phase. At the female phase, the oocytes of several developmental stages were observed including gonial germ cells in the periphery of ovigerous lamellae. At the beginning of ET phase, perinucleolar and previtellogenic oocytes began degenerating, followed by proliferation of spermatogonia toward the center of lamella. The LT phase was characterized by further degeneration of oocytes and rapid proliferation of spermatogenic germ cells throughout the gonad. At the male phase, no ovarian cells were observed and testis had germ cells undergoing active spermatogenesis. Serum levels of estradiol-17beta (E2) were high in females in the breeding season, but low in the non-breeding female, transitional and male phase, and those of 11-ketotestosterone (11-KT) and testosterone (T) were low in females and gradually increased in the transitional and male phase. The present results suggest that low serum E2 levels and degeneration of oocytes accompanied by concomitant increase in the 11-KT levels and proliferation of spermatogenic germ cells are probably the events mediating protogynous sex change in the honeycomb grouper.     

Premature decline of serum total testosterone in HIV-infected men in the HAART-era

Background

Testosterone (T) deficiency remains a poorly understood issue in men with Human Immunodeficiency Virus (HIV). We investigated the gonadal status in HIV-infected men in order to characterize T deficiency and to identify predictive factors for low serum T.

Methodology/Principal Findings

We performed a cross-sectional, observational study on 1325 consecutive HIV male outpatients, most of them having lipodystrophy. Serum total T<300 ng/dL was used as the threshold for biochemical T deficiency. Morning serum total T, luteinizing hormone (LH), estradiol, HIV parameters, and body composition parameters by CT-scan and Dual-Energy-X-ray-Absorptiometry were measured in each case. Sexual behavior was evaluated in a subset of 247 patients. T deficiency was found in 212 subjects, especially in the age range 40–59, but was frequent even in younger patients. T deficiency occurred mainly in association with low/normal serum LH. Adiposity was higher in subjects with T deficiency (p<0.0001) and both visceral adipose tissue and body mass index were the main negative predictors of serum total T. Osteoporosis and erectile dysfunction were present in a similar percentage in men with or without T deficiency.

Conclusions/Significance

Premature decline of serum T is common (16%) among young/middle-aged HIV-infected men and is associated with inappropriately low/normal LH and increased visceral fat. T deficiency occurs at a young age and may be considered an element of the process of premature or accelerated aging known to be associated with HIV infection. The role of HIV and/or HIV infection treatments, as well as the role of the general health state on the gonadal axis, remains, in fact, to be elucidated. Due to the low specificity of signs and symptoms of hypogonadism in the context of HIV, caution is needed in the diagnosis of hypogonadism in HIV-infected men with biochemical low serum T levels.     

Circadian regulation of pineal melatonin and reproduction in the Djungarian hamster

Gonadal state, pineal melatonin rhythms, and locomotor activity rhythms were examined in juvenile male Djungarian hamsters exposed to non-24-hr light cycles ("T-cycles") or to full photoperiods. At the end of 1 month, hamsters exposed to a 1-hr pulse of light every 24.33 hr (T 24.33) exhibited small testes, whereas those receiving the same amount of light every 24.78 hr (T 24.78) displayed stimulated gonads, ten-fold larger in size. Accompanying the nonstimulatory effect of the T 24.33 cycle were nocturnal peaks in both pineal melatonin content and serum melatonin concentration which were longer by approximately 4 hr than those observed on the photostimulatory T 24.78 cycle. Exposure to an intermediate-length T-cycle (T 24.53) resulted in a mixed gonadal response and in pineal and serum melatonin peaks of intermediate duration. Wheel-running activity was entrained to the T-cycles such that light was present only near the beginning of the subjective night, its phase (relative to activity onset) differing only slightly among T-cycle groups. Hence the durational differences observed in the melatonin peaks were apparently not due to the acute suppressive or phase-advancing effects of morning light on melatonin biosynthesis, but were rather the result of differences in the endogenous control of pineal activity by the circadian pacemaker system. While no strong correlation was detected between gonadal state and the phase of locomotor activity onset relative to the light pulse, a significant correlation was observed between gonadal state and the duration of daily locomotor activity (alpha). These data were compared to similar measures obtained from hamsters exposed to long-versus short-day full photoperiods (LD 16:8 vs. LD 10:14). In summary, the results of this study indicate involvement of the circadian pacemaker system of Djungarian hamsters in the control of pineal melatonin synthesis and secretion, and in photoperiodic time measurement. Furthermore, these data strengthen the hypothesis that it is the duration of nocturnal pineal melatonin secretion that is the critical feature of this neuroendocrine gland's photoperiodic signal.     

Expression of nerve growth factor (NGF), and its receptors TrkA and p75 in the reproductive organs of the adult male rats

Immunolocalization of nerve growth factor (NGF) and its receptors, TrkA and p75 in the reproductive organs of adult male rats was investigated. Sections of the testis, efferent duct, epididymis, deferent duct, seminal vesicle, coagulating gland and prostate of adult male rats were immunostained by the avidin-biotin-peroxidase complex methods (ABC). NGF was expressed in Leydig cells, primary spermatocytes and pachytene spermatocytes in the testis. TrkA only immunoreacted to elongate spermatids and p75 showed positive immunostaining in the Sertoli cells, Leydig cells, the pachytene spermatocytes and elongate spermatids. Immunoreactions for NGF and its two receptors were detected in epithelial cells of efferent duct, deferent duct and epididymis. In addition, immunoreactions for NGF and its two receptors were also observed in columnar secretory epithelium lines of the seminal vesicles, prostate and coagulating gland. These results suggest that NGF is an important growth factor in gonadal function of adult male rats.