Effects of induced hypoprolactinemia on testicular function during gonadal maturation in the rat

Exogenous arachidonate restores the dimethoate-induced inhibition of steroidogenesis in rat interstitial cells

The present work studies the potential restorative effect of polyunsaturated fatty acids (PUFA, 5 μM/24 h) on the dimethoate (DMT)-induced inhibition of testosterone biosynthesis in Leydig cells isolated from rat testes. Various fatty acids (FA) from the n-6 (18:2, 20:3, 20:4, 22:4 and 22:5) and n-3 (18.3, 20:5, 22:5, 22:6) series were assayed in Leydig cells, alone (as delipidated BSA complexes) and in combination with DMT (1 ppm). The n-6 FA stimulated lipid peroxidation (LPO) and inhibited the activities of steroidogenic enzymes (3β- and 17β-hydroxysteroid dehydrogenases). The n-3 FA exerted an anti-oxidant effect, decreasing the production of thiobarbituric-acid reactive substances (TBARS) and inhibiting phospholipase A(2) activity. The biosynthesis of testosterone in DMT-treated cultures was completely normalized by ARA (20:4n-6) and partially restored by the addition of 20:3n-6, increasing ARA content inside the mitochondria. The other FA assayed failed to restore androgenesis. COX-2 protein and prostaglandin F2α and E2 production were stimulated by 20:3n-6, ARA, 18:3n-3 and 20:5 n-3. COX-2 protein decreased upon addition of 22:5n-3 and 22:6n-3. StAR protein was increased by ARA and partially increased by 20:3n-6, likely due to its metabolic conversion into ARA. Both FA increased the mitochondrial cholesterol pool available for testosterone biosynthesis. The rate of androgenesis is likely the result of various regulatory factors acting concomitantly on the physiology of Leydig cells.

Functions of TAM RTKs in regulating spermatogenesis and male fertility in mice

Mice lacking TYRO3, AXL and MER (TAM) receptor tyrosine kinases (RTKs) are male sterile. The mechanism of TAM RTKs in regulating male fertility remains unknown. In this study, we analyzed in more detail the testicular phenotype of TAM triple mutant (TAM−/−) mice with an effort to understand the mechanism. We demonstrate that the three TAM RTKs cooperatively regulate male fertility, and MER appears to be more important than AXL and TYRO3. TAM−/− testes showed a progressive loss of germ cells from elongated spermatids to spermatogonia. Young adult TAM−/− mice exhibited oligo-astheno-teratozoospermia and various morphological malformations of sperm cells. As the mice aged, the germ cells were eventually depleted from the seminiferous tubules. Furthermore, we found that TAM−/− Sertoli cells have an impaired phagocytic activity and a large number of differentially expressed genes compared to wild-type controls. By contrast, the function of Leydig cells was not apparently affected by the mutation of TAM RTKs. Therefore, we conclude that the suboptimal function of Sertoli cells leads to the impaired spermatogenesis in TAM−/− mice. The results provide novel insight into the mechanism of TAM RTKs in regulating male fertility.

Involvement of lipids in dimethoate-induced inhibition of testosterone biosynthesis in rat interstitial cells

The mechanism involved in the inhibition of testosterone (Te) biosynthesis after a sub-chronic exposure to low doses of dimethoate (D) was studied in rat interstitial cells (IC). Expression of COX-2 in IC isolated from D-treated rats increased by 44% over C data, while transcription of StAR decreased by approx. 50% and the expression of this protein was diminished by approximately 40%. PGE(2) and PGF(2alpha) were increased by 61 and 78%, respectively. Te concentration decreased by 49% in IC homogenates. Concomitantly, plasma concentration of LH and FSH both increased. Araquidonate (ARA) and C(22) fatty acyl chains in phospholipids from IC mitochondrial fraction decreased by approx. 30% after D treatment. Protein carbonyls, lipoperoxides and nitrite content increased while alpha-tocopherol and the antioxidant capacity of the soluble cellular fraction decreased significantly. Stimulation with h-CG 10 nM overnight failed to overcome the inhibition caused by D on both Te biosynthesis and 3beta- and 17beta-hydroxysteroid dehydrogenases. Decreased Te biosynthesis may be attributed to (1) inhibition of StAR protein activity due to the stimulation of COX-2 and the overproduction of PGF(2alpha), (2) decreased stimulatory effect of ARA on StAR with a subsequent reduction in the availability of CHO for the androgenic pathway, and/or (3) indirect inhibition of steroidogenic enzymes by a lower transcriptional rate caused by elevated PGF(2alpha). Rofecoxib administration prevents the deleterious effect(s) exerted by D.

Functional and phenotypic characteristics of testicular macrophages in experimental autoimmune orchitis

Testicular inflammation with compromised fertility can occur despite the fact that the testis is considered an immunoprivileged organ. Testicular macrophages have been described as cells with an immunosuppressor profile, thus contributing to the immunoprivilege of the testis. Experimental autoimmune orchitis (EAO) is a model of organ-specific autoimmunity and testicular inflammation. EAO is characterized by an interstitial inflammatory mononuclear cell infiltration, damage of the seminiferous tubules and germ cell apoptosis. Here we studied the phenotype and functions of testicular macrophages during the development of EAO. By stereological analysis, we detected an increased number of resident (ED2+) and non-resident (ED1+) macrophages in the testicular interstitium of rats with orchitis. We showed that this increase was mainly due to monocyte recruitment. The in vivo administration of liposomes containing clodronate in rats undergoing EAO led to a reduction in the number of testicular macrophages, which correlated with a decreased incidence and severity of the testicular damage and suggests a pathogenic role of macrophages in EAO. By immunohistochemistry and flow cytometry we detected an increased number of testicular macrophages expressing MHC class II, CD80 and CD86 costimulatory molecules in rats with orchitis. Also, testicular macrophages from rats with EAO showed a higher production of IFNgamma (ELISA). We conclude that testicular macrophages participate in EAO development, and the ED1+ macrophage subset is the main pathogenic subpopulation. They stimulate the immune response through the production of pro-inflammatory cytokines and antigen presentation and thus activation of T cells in the target organ.

Effect of steroid hormones onBufo arenarum oviduct. Ultrastructural study

The endocrine regulation of the mucosa of the oviductal pars convoluta was analyzed by ultrastructural studies demonstrating that ovariectomy, together with a decrease in ovarian steroids circulating levels, caused a marked regression in this portion of Bufo arenarum oviduct. Twenty-five days after ovariectomy, a decrease in the depth of the epithelial and glandular layers was observed due to the notable loss of secretory cells, whose number was clearly smaller than in nonovariectomized females. The remaining secretory cells showed involution signs, with few secretory granules in their cytoplasm, little endoplasmic reticulum near poorly developed Golgi complexes and a large amount of lipid droplets. Cells in an advanced autolysis state were found in the lumen. These characteristics evidence a nonfunctional state of the pars convoluta. Treatment with 5alpha-dihydrotestosterone (DHT) completely reversed the ovariectomy effect, inducing pars convoluta growths and restoring the characteristics of epithelial and glandular secretory cells in the whole pars convoluta, with micrographs similar to the control. These same effects were observed after treatment with estradiol-17beta (E2), progesterone (P) o E(2)+P in the glandular layer of the whole pars convoluta, but only in the epithelial layer of the most anterior region of this duct. In the secretory cells of other segments these treatments induced the formation of granules of high electron density and homogeneous aspect. Each steroid had a particular effect on the pars convoluta. Although E2 and DHT induced the development of the organoids involved in the proteins biosynthesis, P and DHT acted as secretagogues.

Testis structure and function in a nongenetic hyperadipose rat model at prepubertal and adult ages

There are few data for hormonal levels and testis structure and function during postnatal development in rats neonatally treated with monosodium L-glutamate (MSG). In our study, newborn male pups were ip injected with MSG (4 mg/g body weight) every 2 d up to 10 d of age and investigated at prepubertal and adult ages. Plasma levels of leptin, LH, FSH, prolactin, testosterone (T), corticosterone, and free T4 (FT4) were measured. MSG rats displayed elevated circulating levels of corticosterone and hyperadiposity/hyperleptinemia, regardless of the age examined; conversely, circulating prolactin levels were not affected. Moreover, prepubertal MSG rats revealed a significant (P < 0.05) reduction in testis weight and the number of Sertoli (SC) and Leydig cells per testis. Leptin plasma levels were severalfold higher (2.41 vs. 8.07; P < 0.05) in prepubertal MSG rats, and these animals displayed plasma LH, FSH, T, and FT4 levels significantly decreased (P < 0.05). Taken together, these data indicate that testis development, as well as SC and Leydig cell proliferation, were disturbed in prepubertal MSG rats. Adult MSG rats also displayed significantly higher leptin plasma levels (7.26 vs. 27.04; P < 0.05) and lower (P < 0.05) LH and FSH plasma levels. However, T and FT4 plasma levels were normal, and no apparent alterations were observed in testis structure of MSG rats. Only the number of SCs per testis was significantly (P < 0.05) reduced in the adult MSG rats. In conclusion, although early installed hyperadipose/hyperleptinemia phenotype was probably responsible for the reproductive axis damages in MSG animals, it remains to be investigated whether this condition is the main factor for hypothalamus-pituitary-gonadal axis dysfunction in MSG rats.

Changes in serum sex steroid levels throughout the reproductive cycle of Bufo arenarum females

The changes in the serum levels of the sexual steroids estradiol-17beta (E(2)), testosterone (T), dihydrotestosterone (DHT), and progesterone (P) in Bufo arenarum females were determined by radioimmunoassay (RIA) during 3 consecutive cycles (1999-2001). The serum concentrations of T and DHT, which showed a close parallelism during the annual reproductive cycle, exhibited the highest levels during the preovulatory period, when oogenesis is advanced, while lowest serum levels of these hormones were found during the ovulatory period. The data obtained for E(2) showed a pattern contrary to that determined for androgens. The maximum E(2) concentrations detected in the early postovulatory period might be associated with vitellogenesis and follicular growth. Lowest E(2) concentrations were reached during the period in which B. arenarum undergoes its final hibernation stage. Serum P showed a peak during the preovulatoy period, related to the induction of nuclear maturation in full grown oocytes. A strong decrease in the levels of the circulating hormones was observed after ovariectomy. Our results showed that, out of the four hormones examined, T and DHT were the best indicators of ovarian and oviductal stage, as shown by the strong positive correlation found between androgen levels and organ weight, while E(2) showed a weak negative correlation with ovarian and oviductal weight.

Involvement of tumor necrosis factor-alpha in the pathogenesis of autoimmune orchitis in rats

We studied the testicular macrophages of rats with experimental autoimmune orchitis (EAO) and analyzed whether the tumor necrosis factor-alpha (TNFalpha) is involved in germ cell apoptosis and in Leydig cell steroidogenesis. The EAO was induced in adult male Sprague-Dawley rats by active immunization with testicular homogenate and adjuvants. In the experimental group, a severe orchitis was observed 80 days after the first immunization. ED1- and ED2-positive macrophages were quantified by immunohistochemistry. The TNFalpha concentration of conditioned media from testicular macrophages (TMCM) was determined by ELISA. The number of apoptotic TNF receptor 1 (TNFR1)-positive germ cells was identified by combining in situ end labeling of apoptotic DNA and immunohistochemical techniques. The effect of TNFalpha on Leydig cell testosterone production was determined by RIA. In rats with EAO, we observed a significant increase in the number of TNFalpha-positive testicular macrophages, the TNFalpha concentration in TMCM, and the number of TNFR1-positive germ cells. Sixty percent of TNFR1-positive germ cells were apoptotic. These results suggest that TNFalpha could be involved in the pathogenesis of EAO. Acting together with other local factors such as Fas-FasL, TNFalpha could trigger germ cell apoptosis. We also demonstrated that TNFalpha inhibited in vitro testosterone production in basal and hCG-stimulated Leydig cells from rats with orchitis.

Role of prolactin in the regulation of cytosolic NADP isocitrate dehydrogenase in the liver of the male rat

The activity of cytosolic NADP-linked isocitrate dehydrogenase (ICDH) in rat liver was determined. The administration of 2-bromo-alpha-ergocryptine (CB-154) to male rats produced a significant increase of the enzyme activity and a decrease of serum prolactin (PRL) levels in relation to control animals. Male rats 21 days after castration had lower levels of serum prolactin and higher activity of the enzyme than controls. Injection of PRL to castrated male rats lowered the enzymatic activity to control values. In intact rats injected with prolactin, the activity of the enzyme also decreased. Female rats were separated into the following groups: (a) virgins; (b) rats on day 15 of lactation; (c) ovariectomized rats. The enzymatic activity was similar in the different groups, but significantly higher than in male rats. However, serum PRL was significantly increased in 15 days lactating rats and decreased in ovariectomized ones in relation to virgins. We conclude that PRL regulates hepatic ICDH activity in male, but not in female rats. Incubation of isolated hepatocytes from intact or castrated male rats maintained the difference in ICDH activity observed in vivo, while there were no differences in ICDH activity in non-parenchymal cells. Addition of PRL, CB-154, androgens or antiandrogens to isolated hepatocytes from intact and castrated rat, had no effect on the ICDH activity, suggesting that the effect of PRL is exerted at the transcriptional level.

Endocrine-disrupting chemicals: prepubertal exposures and effects on sexual maturation and thyroid function in the male rat. A focus on the EDSTAC recommendations. Endocrine Disrupter Screening and Testing Advisory Committee

Puberty in mammalian species is a period of rapid interactive endocrine and morphological changes. Therefore, it is not surprising that exposure to a variety of pharmaceutical and environmental compounds has been shown to dramatically alter pubertal development. This concern was recognized by the Endocrine Disrupter Screening and Testing Advisory Committee (EDSTAC) that acknowledged the need for the development and standardization of a protocol for the assessment of the impact of endocrine-disrupting compounds (EDC) in the pubertal male and recommended inclusion of an assay of this type as an alternative test in the EDSTAC tier one screen (EPA, 98). The pubertal male protocol was designed to detect alterations of pubertal development, thyroid function, and hypothalamic-pituitary-gonadal (HPG) system peripubertal maturation. In this protocol, intact 23-day-old weanling male rats are exposed to the test substance for 30 days during which pubertal indices are measured. After necropsy, reproductive and thyroid tissues are weighed and evaluated histologically and serum taken for hormone analysis. The purpose of this review was to examine the available literature on pubertal development in the male rat and evaluate the efficacy of the proposed protocol for identifying endocrine-disrupting chemicals. The existing data indicate that this assessment of puberty in the male rat is a simple and effective method to detect the EDC activity of pesticides and toxic substances.

Influence of age and photoperiod on steroidogenic function of the testis in the golden hamster

The golden (Syrian) hamster is a seasonal breeder, and exposure of adult animals to short days results in severe gonadal regression with morphological features that resemble the immature testis. The purpose of this study was to investigate testicular steroidogenic capacity in the golden hamster and to analyse the influence of age and photoperiod on this process. Hamsters aged 36 days were maintained on a long photoperiod (14L:10D), and adult animals were then exposed to a long or a short photoperiod (6L:18D) for 14 weeks (the period of time required to achieve maximal gonadal regression), to assess circulating levels and in vitro production of testosterone, dihydrotestosterone and androstane-3 alpha, 17 beta-diol. In peripubertal hamsters, androstane-3 alpha, 17 beta-diol was the main circulating androgen detected, whereas in active adult animals, testosterone showed the highest serum levels. In hamsters exposed to a short photoperiod, blood testosterone levels were significantly lower than levels in adult hamsters exposed to a long photoperiod. Exposure of adult hamsters to a short photoperiod produced a marked reduction in serum concentrations of dihydrotestosterone and androstane-3 alpha, 17 beta-diol, which was not accompanied by a decrease in testicular 5 alpha-reductase activity. In the in vitro experiments, active adult testes were less sensitive than inactive adult testes to stimulation of androgen production with hCG, but showed similar sensitivity to the gonads from hamsters aged 36 days. In accordance with circulating androgen concentrations, the principal androgens produced in the in vitro assays from peripubertal and normal adult testes were androstane-3 alpha, 17 beta-diol and testosterone, respectively. Unexpectedly, the main androgen produced from regressed testes under in vitro conditions was androstane-3 alpha, 17 beta-diol. Inactive gonads released more androstane-3 alpha, 17 beta-diol than did normal adult testes and total in vitro androgen production (testosterone + dihydrotestosterone + androstane-3 alpha, 17 beta-diol) from adult testes was not diminished by exposure to a short photoperiod. However, in spite of the significant increase detected in production of androstane-3 alpha, 17 beta-diol in vitro from regressed testes, inactive gonads produced less androstane-3 alpha, 17 beta-diol than did peripubertal testes. In summary, our studies suggest that testicular androgen biosynthetic capacity in adult hamsters exposed to short photoperiod is not reduced and these regressed testes represent an intermediate physiological state between peripubertal and active adult testes. The significant decrease detected in serum androgen concentrations during the involution phase could result from the absence of stimulating pituitary factors, together with a negative regulation of steroidogenesis by different non-steroidal signals originating within and/or outside of the testis.

Lipid dismetabolism in Leydig and Sertoli cells isolated from streptozotocin-diabetic rats

This work evaluates how the abnormalities in fatty acid biosynthesis, already described in diabetic rats, were extended to Sertoli and Leydig cells isolated from testes of streptozotocin-treated rats. Both kinds of cells were incubated in the presence of labeled eicosa-8,11,14-trienoic acid. The uptake of the substrate and its conversion to arachidonic acid were significantly depressed in both cell types compared to the non-diabetic controls. The indirect evidence of this inhibition was observed in the total fatty acid pattern of the cells where the 20:4 n-6/18:2 n-6 ratio was significantly decreased. The addition of insulin to the incubation medium produced no changes in the uptake of the substrate by the cells. Under similar experimental conditions the synthesis of arachidonic acid was partially recovered, however, the values obtained were still below those ones of cells isolated from control animals. These results were correlated with the fatty acid profile of different lipid fractions of plasma and with the activity of enzymes involved in polyunsaturated fatty acids biosynthesis measured in the testicular microsomes of diabetic rats. We conclude that Sertoli and Leydig cells evidenced similar lipid disorders than those observed in the whole testis or in other tissues of diabetic rats, and that the biosynthesis of arachidonic acid is under insulin regulation.

Ornithine decarboxylase activity and polyamine levels in the epididymis of prepubertal rat after antiandrogen administration

The antiandrogens flutamide and casodex have been administered subcutaneously (vehicle, 1, 5 or 10 mg per day) to prepubertal male rats for 10 days. A significant change of epididymal weight has been observed after both treatments, from the lowest dose used. Epididymal dihydrotestosterone concentrations were significantly increased in flutamide- or casodex-treated rats, while epididymal 3 alpha-androstanediol concentrations were affected only after flutamide administration, suggesting a differential effect on androgen metabolism between both antiandrogens. Ornithine decarboxylase (ODC) activity was significantly decreased by flutamide, and to a lesser extent by casodex. Antiandrogen administration resulted in a significant decrease in epididymal content of the polyamines putrescine, spermidine, and spermine. A slight but significant decrease in putrescine and spermidine concentrations, but not in spermine, was observed after flutamide treatment. However, casodex had no effects on polyamines levels. A decrease in putrescine concentration was detected only when ODC activity fell to rather low levels. Interference of the antiandrogens with the biological action of androgens on ODC activity was clearly seen in immature male rats. Therefore, both epididymal growth and differentiation, in correlation to ODC activity, would be severely affected at an early period of sexual development, such as prepuberty.

Influence of photoinhibition on GABA and glutamic acid levels, and on glutamate decarboxylase activity in the testis and epididymis of the golden hamster

Gamma-aminobutyric acid (GABA) is found in the gonads and accessory reproductive organs, and a direct effect on steroidogenesis and sperm viability and motility has been described. The golden (Syrian) hamster is a seasonal breeder, and a pattern of regression-recrudescence in their reproductive organs is observed when adult animals are exposed to less than 12.5 h daylight for an extended period of time. The purpose of this study was to investigate: (1) the presence of GABA in the testis and epididymis of golden hamsters undergoing regression and spontaneous recrudescence; (2) glutamic acid levels and glutamate decarboxylase (GAD) activity in both tissues, and (3) testicular and epididymal testosterone, dihydrotestosterone and 5 alpha-androstane-3 alpha, 17 beta-diol concentrations. Adult golden hamsters were exposed to long (LP 14L:10D) or short (SP 6L:18D) photoperiods for 9, 12, 14, 16, 18 or 22 weeks. When animals were exposed to SP for 14-16 weeks, the testis and epididymis reached maximal involution. Testicular and epididymal androgen levels showed a marked decrease (p < 0.05) during the regression period, and after 18-22 weeks, values began to recover. Between 12 and 18 weeks in SP, the testicular and epididymal content of GABA and glutamic acid was reduced significantly. The concentration of GABA in both tissues showed a sharp rise (p < 0.05), while the concentration of glutamic acid diminished during the period of maximal involution (p < 0.05). In the testis, GAD activity was increased (p < 0.001) after 14 weeks in SP, with no change in the epididymis. In conclusion, glutamic acid via GAD activity could be the main source of GABA in the testis, but not in the epididymis. Furthermore, the presence of GABA in testicular cells and its subsequent photoperiodic variations might act as an important autocrine and/or paracrine modulatory signal in gonadal processes.

Testicular gamma-aminobutyric acid and circulating androgens in Syrian and Djungarian hamsters during sexual development

Several factors, besides luteinizing hormone (LH), participate in the modulation of testicular function. A number of neurotransmitters are reported to be involved in this process, including a stimulatory action of gamma-aminobutyric acid (GABA) on steroidogenesis in the rat testis. The purpose of this study was to investigate the testicular pattern of GABA and glutamic acid, one of its main precursors, during sexual maturation in two seasonally breeding species: Syrian (golden) and Djungarian hamsters. Plasma androgen levels were also measured. The animals were maintained under long-day photoperiod (16:8, L:D) and were killed at 23, 30, 36, 46, 60, and 90 days of age. A different pattern of developmental changes in body and testicular weight was observed in these two species. GABA was present in the testes at all ages studied. GABA concentration and content showed a sharp elevation in the prepubertal period in golden as well as Djungarian hamsters. However, glutamic acid concentrations remained nearly constant during development in both species. Glutamic acid content increased gradually with age in the golden hamster, while a marked peak at 36 days of age was detected in the Djungarian hamster. Plasma testosterone and dihydrotestosterone levels were maximal at pubertal age in both species. The plasma levels of 5 alpha-androstane-3 alpha, 17 beta-diol increased significantly at 30 days of age in the golden hamster while in Djungarian hamsters this steroid remained unchanged. These results suggest that glutamic acid may serve as a precursor for GABA biosynthesis in the testis. In addition, changes in testicular GABA and plasma androgen levels might reflect a modulatory effect of this neurotransmitter in the acquisition of steroidogenic capability during development.

Modulation of ornithine decarboxylase activity by prolactin in seminal vesicles of the rat

The stimulatory effect of prolactin on sexual accessory glands is well established, though the mechanism of trophic action remains poorly understood. We have therefore assessed the effect of high levels of prolactin on ornithine decarboxylase activity and polyamine content in seminal vesicles (SV) of adult rats. Hyperprolactinaemia was induced by implantation of tissue fragments of a prolactin-secreting tumour 7315a, and the rats killed at 35 days post-inoculation. Serum levels of prolactin were increased significantly (p < 0.001) in tumour-bearing rats. Levels of testosterone in serum were reduced markedly, whereas LH levels remained unchanged. SV weight in the experimental group was not significantly different from that in the corresponding control group. A clear increase in ornithine decarboxylase activity of SV was observed (p < 0.001) in the hyperprolactinaemic rats. However, there was no change in the polyamine content of SV in tumour-bearing rats, compared to the control group. These results indicate that ornithine decarboxylase activity in SV of adult rats is regulated mainly by prolactin. This experimental model may be useful for identification of some of the events involved in the trophic action of prolactin.

Bromocriptine-induced inhibition of hydroxylase/lyase activity of adult rat Leydig cells

The present in vitro studies using a suspension of Leydig cells from adult rat testis demonstrated that bromocriptine (BR, 2 x 10(-5)M) inhibits hCG-stimulated testosterone production (in the presence of submaximal and maximal doses of hCG), while basal production was unaffected. When the cells were exposed to 8-bromo-cAMP either in the presence or absence of hCG, the inhibitory effect of BR was not reversed. In intact cells, BR inhibited conversion of progesterone and 17-hydroxy-progesterone to testosterone while conversion of androstenedione was not affected. Incubation of homogenates of Leydig cells in the presence of limiting NADPH concentrations (< or = 0.1 mM) resulted in significant BR-induced inhibition of conversion of progesterone (10 microM) to testosterone, while in the presence of "high" concentrations of NADPH (> or = 0.5 mM) BR was without effect. Present results suggest that BR inhibits androgen production at the level of the microsomal enzymes 17 alpha-hydroxylase and/or 17,20-lyase. The inhibitory effect of BR using homogenates of Leydig cells was evident only in the presence of limiting NADPH concentrations that suggests a competitive-like pattern of inhibition, but mechanisms by which BR decreases activity of microsomal enzymes remain to be determined.

Arachidonic acid biosynthesis in non-stimulated and adrenocorticotropin-stimulated Sertoli and Leydig cells

The biosynthesis of arachidonic acid in Sertoli and Leydig cells isolated from the testes of mature rats has been investigated. Both types of cells incorporated [2-14C]eicosatrienoic acid from the incubation medium and transformed it into arachidonic acid. The administration of adrenocorticotropin (ACTH) to the rats decreased the delta 5 desaturating activity in the isolated testicular cells, while ACTH produced no changes in the uptake of the substrate. Similar results were obtained when ACTH was added to the incubation medium of cells isolated from non-hormone treated rats. The total fatty acid composition of the Sertoli cells isolated from ACTH-treated rats showed a significant increase in the relative percentage of 18:2n-6 and a decrease in the C20 and C22 polyenes. This may indicate that ACTH exerts an inhibitory effect on delta 6, delta 5 and delta 4 desaturase activities. Addition of corticosterone to the incubation medium also produced a significant decrease in arachidonic acid biosynthesis. Because ACTH is known to stimulate the release of corticosterone in vivo, both hormones may act cumulatively in the regulation of arachidonic acid metabolism in Sertoli and Leydig cells.

Coexistence of gamma-aminobutyric acid type A and type B receptors in testicular interstitial cells

The existence of specific gamma-aminobutyric acid (GABA)ergic receptors in testicular interstitial cells was investigated in the present study. Specific binding of [3H]GABA to interstitial cell membranes was found to be time- and temperature-dependent and varied according to Ca2+ concentration present in the incubation medium. We analyzed the ability of different GABAergic agonists and antagonists to displace the bound radioactivity. In the absence of Ca2+ (1 mM EDTA), GABA and the GABAergic agonist isoguvacine displaced the bound radioactivity. When the radioligand assay was performed in the presence of 2.5 mM CaCl2, the [3H]GABA specifically bound increased twofold. Under such conditions, the specific GABAergic agonist baclofen, as well as GABA and isoguvacine, displaced the [3H]GABA bound. Saturation analysis revealed the presence of a population of GABAA binding sites with a KD value of 45.2 nM and a maximal number of binding sites of 57.4 fmol/mg of protein. The maximal binding increased on addition of 2.5 mM CaCl2 to 102 fmol/mg of protein, indicating the existence of a second population of GABAergic receptors, i.e., type B, with essentially the same affinity. In addition, the incubation of testicular interstitial cells with GABA and baclofen resulted in an increase in androgen production. These results support a functional role of GABA in the neuroendocrine control of the male gonad.

Effect of an antiestrogen on the testicular response to acute and chronic administration of hCG in normal and hypogonadotropic hypogonadic men: tamoxifen and testicular response to hCG

The effect of the antiestrogen tamoxifen (Tx) on the acute and chronic hCG administration was evaluated in patients with hypogonadotropic hypogonadism (HH) and in normal men. An hCG test (5000 IU hCG) was performed before, after two months of hCG administration (2000 IU hCG three times weekly) and after two months of hCG + Tx (2000 IU hCG three times weekly plus 20 mg/day of tamoxifen). Blood samples were obtained before and following 24 and 72 h of every test to determine T, E, 17OHP and SHBG. T increased only in HH with both treatments (X +/- SEM: Basal: 97.9 +/- 19.7; hCG: 237.7 +/- 43.2; hCG +/- Tx: 204.7 +/- 10.7 ng/100 ml). 17OHP rose with hCG alone, but not with hCG + Tx in both groups. E, SHBG and 17OHP/T ratio did not change after treatments. hCG tests: E increased 24 h following hCG administration in every test. The ratio 17OHP/T rose at 24 h in the first and second test but in the third test it did not change. These results support the role of E in the acute hCG-induced Leydig cell desensitization. However, the association of Tx does not improve T serum levels, suggesting that E might not be the unique factor involved in the mechanisms for testicular desensitization.

Effect of long term diazepam administration on testicular benzodiazepine receptors and steroidogenesis

We evaluated the effect of acute and chronic diazepam administration on testicular peripheral type benzodiazepine receptors (PBZD-R), serum testosterone and LH levels and the "in vitro" androgen production in response to Ro 5-4864, a PBZD-R agonist. The chronic diazepam treatment induced a significant fall in plasma testosterone concentration while LH levels remained unchanged. The number of PBZD-R was reduced by 37% and low concentrations (10(-8)-10(-6) M) of Ro 5-4864 failed to stimulate "in vitro" androgen production. The acute diazepam administration caused a significant increase in plasma testosterone levels while no changes were observed in LH concentrations and testicular PBZD-R. These results further suggest a modulatory role of PBZD-R on testicular steroidogenic activity.

Effects of prolactin on luteinizing hormone-stimulated testosterone secretion in isolated perfused rat testis

The direct peripheral effect of prolactin on LH-stimulated testosterone secretion was re-evaluated using the intact, isolated, perfused rat testis. In paired experiments, one testis was infused with the hormones being studied; the other testis of the same rat was used as the control. A dose-response curve of LH-stimulated testosterone secretion was established first. A dose of 300 ng of LH, which was on the ascending portion of the dose-response curve, was selected so that both stimulatory and inhibitory effects of prolactin could be observed. Prolactin doses ranging from 0 ng to 3000 ng were then tested to determine alterations in LH-stimulated testosterone secretion. Prolactin inhibited LH-stimulated testosterone secretion at low doses (less than 300 ng), but augmented LH action at high doses (greater than 1000 ng). These results showed that prolactin and LH interact with each other in a biphasic dose-dependent manner.

Effect of GABA and benzodiazepines on testicular androgen production

We have evaluated the effect of Ro5-4864, a selective probe to label peripheral type benzodiazepine receptor, on "in vitro" testicular androgen production. Decapsulated testes from adult rats showed a significant increase in the basal and hCG-stimulated testosterone secretion into the medium in response to 10(-5) M, 10(-6) M, and 10(-7) M Ro5-4864. In addition, we have studied the changes in testicular GABA content at three different ages and we found its highest concentration at 31 days of age. When we evaluated the effect of GABA on "in vitro" androgen production at different stages of gonadal maturation we observed that the highest concentration of GABA (10(-6) M) was able to modify the basal and hCG-stimulated androgen production from adult (60 days) and pubertal (45 days) testes. In addition, when prepubertal testes (31 days) were incubated under basal conditions, 10(-6) M GABA induced a significant increment of androstanediol production, while the stimulatory effect of hCG was reduced in the presence of the same GABA concentration. The present results suggest that GABA plays a physiological role in the regulation of rat testicular androgen production depending on the stage of sexual maturation.