Effects of hyperprolactinemia on testosterone production in rat Leydig cells

Expression and regulation of GnRHR2 gene and testosterone secretion mediated by GnRH2 and GnRHR2 within porcine testes

Gonadotropin-releasing hormone 2 receptor (GnRHR2) together with its cognate ligand involves in regulating reproductive behavior. However, little is known concerning the effect of transcription factor steroidogenic factor1 (SF-1) regulation on porcine GnRHR2 gene expression and GnRH2 regulation mechanism in testosterone secretion through GnRHR2. Our study demonstrated that GnRHR2 transcription levels were high in porcine testis. Immunohistochemistry analyses showed that GnRHR2 immunoreactivity was strong in the Leydig cells in boar testes. Two SF-1 binding sites were predicted in GnRHR2 promoter and the second site (-159/-149) was considered to be important for GnRHR2 promoter activity through site-directed mutagenesis. The binding of SF-1 to GnRHR2 promoter was confirmed by electrophoretic mobility shift assays (EMSA) and chromatin immunoprecipitation (ChIP). Overexpression and knockdown experiments revealed that SF-1 could up-regulate porcine GnRHR2 expression. DNA methylation of GnRHR2 promoter CpG island also specifically regulated GnRHR2 expression. Meanwhile, our study also demonstrated GnRH2 treatment promoted the expression of SF-1 and steroidogenic acute regulatory protein (StAR), and that this treatment stimulated cAMP responsive element binding protein (CREB) phosphorylation, regulated the expression of GnRHR2, especially that of GnRHR2-X1, and promoted testosterone secretion in porcine Leydig cells. We speculated that testosterone secretion mediated by GnRH2 and GnRHR2 (mainly GnRHR2-X1) was regulated by phosphorylated CREB interacting with SF-1 to control StAR expression. Taken together, the present study indicates that SF-1 and GnRH2 are the essential regulatory factors for GnRHR2 expression. This study also explores the regulation mechanism of testosterone secretion mediated by GnRH2 and GnRHR2 in porcine Leydig cells.

Persistent Hypogonadotropic Hypogonadism in Men After Severe Traumatic Brain Injury: Temporal Hormone Profiles and Outcome Prediction

OBJECTIVE

To (1) examine relationships between persistent hypogonadotropic hypogonadism (PHH) and long-term outcomes after severe traumatic brain injury (TBI); and (2) determine whether subacute testosterone levels can predict PHH.

SETTING

Level 1 trauma center at a university hospital.

PARTICIPANTS

Consecutive sample of men with severe TBI between 2004 and 2009.

DESIGN

Prospective cohort study.

MAIN MEASURES

Post-TBI blood samples were collected during week 1, every 2 weeks until 26 weeks, and at 52 weeks. Serum hormone levels were measured, and individuals were designated as having PHH if 50% or more of samples met criteria for hypogonadotropic hypogonadism. At 6 and 12 months postinjury, we assessed global outcome, disability, functional cognition, depression, and quality of life.

RESULTS

We recruited 78 men; median (interquartile range) age was 28.5 (22-42) years. Thirty-four patients (44%) had PHH during the first year postinjury. Multivariable regression, controlling for age, demonstrated PHH status predicted worse global outcome scores, more disability, and reduced functional cognition at 6 and 12 months post-TBI. Two-step testosterone screening for PHH at 12 to 16 weeks postinjury yielded a sensitivity of 79% and specificity of 100%.

CONCLUSION

PHH status in men predicts poor outcome after severe TBI, and PHH can accurately be predicted at 12 to 16 weeks.

Radiotherapy for prolactin-secreting pituitary tumors

Review the medical and surgical management of patients with prolactinomas and provide an in-depth appraisal of the role of radiotherapy in the treatment of prolactinomas. A thorough review of the pertinent literature was carried out and relevant topics were identified. Topics covered in this comprehensive review include: indications for the use of radiotherapy, choice between conventional radiotherapy and stereotactic radiosurgery, as well as the benefits and potential complications associated with each modality. Due to the excellent response rates with medical management, and rapid symptom relief afforded by resection or debulking surgery in patients who do not respond or tolerate medical therapy, radiotherapy is reserved for patients who do not respond to dopamine agonists and surgery. Both external beam radiotherapy and stereotactic radiosurgery retain important roles in the treatment of refractory or recurrent prolactinomas. Choosing the optimal approach is crucial in maximizing tumor control outcomes and minimizing the risks associated with treatment. The primary determinants of optimal radiation approach are proximity of the tumor to the optic apparatus and tumor size, with radiosurgery being our recommended treatment of choice unless the tumor is larger than 3-4 cm or within 3 mm of the optic nerves, chiasm or tracts. Optimal multidisciplinary management requires the identification of appropriate candidates for radiotherapy in order to take full advantage of treatment options available for each patient.

Assessment of circulating hormones in regulatory toxicity studies II. Male reproductive hormones

When test article-related testicular toxicity or Leydig cell tumors are identified in nonclinical studies, the measurement of circulating hormones such as luteinizing hormone, follicle-stimulating hormone, inhibin, testosterone, or prolactin is often considered in order to aid mechanistic investigations or to identify potential biomarkers in man. Although some hormone levels are relatively constant, others are subject to wide variability owing to pulsatility of secretion, diurnal rhythms, and stress. To avoid being misled, it is important that this variation is factored into any study design that includes hormone measurements. Since all these possibilities start from the pathologist's reading of the tissue sections, we begin with a review of the morphologic changes that are tied to underlying alterations in hormones. We then provide the reader with basic information and representative hormone data, including coefficients of variation, for the major male reproductive hormones in the three main nonclinical species (rats, dogs, and cynomolgus monkeys). Power and probability tables for rats and dogs allow estimates of the number of animals or samples needed to provide a given likelihood of detecting a hormonal change of a given size. More importantly, we highlight the variability of this process and the real value in readers developing this information at their own site.

Role of serum- and glucocorticoid-inducible kinase-1 in regulating torsion-induced apoptosis in rats

Serum- and glucocorticoid-inducible kinase-1 (SGK1) is a serine/threonine protein kinase that responds to various stimuli and mediates cell survival. Although it is known that testicular torsion leads to testicular damage and male infertility, the role of SGK1 in torsion remains unclear. This study investigated whether torsion-induced apoptosis is associated with changes in phosphoinositide-dependent protein kinase-1 (PDK1), SGK1 and forkhead transcription factor FOXO3a expression and/or phosphorylation in rats. Sprague-Dawley rats were divided into four groups: sham (control), 1, 2 and 4 h of unilateral torsion. Bilateral testes, testicular interstitial fluid (TIF) and blood samples were collected immediately after torsion. Our results revealed that SGK1 protein and mRNA were abundantly present in testes and were induced by 2 h of torsion, but that phosphorylation of SGK1, PDK1 and FOXO3a decreased simultaneously. After 2 h of torsion, the testosterone secretion capacity of the primary Leydig cells and testicular interstitial cells (TICs) was impaired and apoptotic spermatogonia and TICs were observed; in addition, the mean seminiferous tubular diameter was decreased. Torsion increased plasma corticosterone levels, but decreased plasma luteinizing hormone and testosterone levels. However, the testosterone levels of the TIF in the ipsilateral testes were significantly enhanced after 2 h of torsion, but suppressed in the contralateral testes. This animal study suggests that PDK1, SGK1 and FOXO3a are involved in torsion-induced apoptosis and that medical therapy should be performed as early as 2 h after the occurrence of torsion to prevent further damage.

Effect of warm-rearing and heat acclimation on pituitary-gonadal axis in male rats

Plasma gonadotrophic and testicular hormones concentrations in both immature and adult male rats exposed to 34 degrees C of ambient temperature were determined. In vitro steroidogenic ability of interstitial cells from experimental rats was also studied. Four groups of rats (n = 45) were used. Warm-reared (WR) males were housed in 34 degrees C and control-reared rats in 20 degrees C from birth to adulthood. The other groups were acclimated to 34 degrees C [warm-acclimated (WA) group] or 20 degrees C [deacclimated (DA) group] as adults. Decreased body weight and testis weight (p < 0.05) was found in heat-exposed groups, but relative testis weight was unchanged in WA and increased (p < 0.05) in WR and DA males. Plasma luteinizing hormone (LH) concentration increased in WA and DA males. Increased (p < 0.05) follicle-stimulating hormone (FSH) and prolactin plasma levels were found in DA and WR groups respectively. WA males had decreased testosterone (T) and WR rats androstenedione (A(4)) plasma concentration (p < 0.05). Interstitial cells (43% of them were Leydig cells by 3beta-hydroxysteroid dehydrogenase activity) from heat-exposed males secreted less (p < 0.05) T compared with the control group when incubated without LH (basal conditions). Androstenedione secretion decreased (p < 0.05) in WA rats. Secretion of estradiol-17beta (E(2)) was higher in WR and lower in DA cells under basal conditions. Weaker responsiveness to LH was observed in WR cells. Androgen synthesis from pregnenolone by interstitial cells increased (p < 0.05) in the WA group. We concluded that heat exposure of neonatal and adult male rats caused different pituitary-testicular axis adjustments. It seemed that long-term heat exposure of neonatal rats is less deleterious concerning the activity of pituitary-testicular axis than heat acclimation of adults.

Effects of arecoline on testosterone release in rats

Arecoline is one of the major components of betel nuts, which have been consumed as chewing gum in Southeast Asia. In this study, the effects of arecoline on testosterone (T) secretion were explored. Male rats were injected with human chorionic gonadotropin (hCG, 5 IU/kg) or arecoline (1 microg/kg) plus hCG via a jugular catheter. Blood samples were collected at several time intervals subsequent to the challenge. Rat anterior pituitary was treated with gonadotropin-releasing hormone in vitro with or without arecoline, and then the concentrations of luteinizing hormone (LH) in the medium were measured. Rat Leydig cells were purified by Percoll density gradient centrifugation and incubated with arecoline, hCG, forskolin, 8-bromo-cAMP (8-Br-cAMP), nifedipine, nimodipine, or tetrandrine at 34 degrees C for 1 h. A single intravenous injection of arecoline resulted in an increase of the hCG-induced level of plasma T. Administration of arecoline (10(-8) to 10(-6) M) in vitro increased T production in Leydig cells. The stimulatory effect of arecoline on T release in vitro was enhanced by hCG (0.001 IU/ml), forskolin (10(-6) M), or 8-Br-cAMP (10(-5) M). By contrast, nifedipine, nimodipine, or tetrandrine inhibited the increased T concentrations induced by arecoline. Western blot showed that arecoline increases steroidogenic acute regulatory (StAR) protein expression compared with vehicle. These results suggested that arecoline stimulates testosterone production by acting directly on Leydig cells via mechanisms involving an activation of L-type calcium channels, increasing the activity of 17beta-hydroxysteroid dehydrogenase and enhancing the expression of StAR.

Effects of renovascular hypertension on reproductive function in male rats

OBJECTIVE

The present study investigated the effects of renovascular hypertension (2K/1C model) on the reproductive function of male rats, represented by sexual behavior, plasma prolactin (PRL), luteinizing hormone (LH), follicle-stimulating hormone (FSH) and testosterone, and spermatogenesis.

METHODS

The present experiments were performed to investigate the reproductive function of 2K/1C male Wistar rats and compare with 2K/1C male rats successfully treated for hypertension with nifedipine and was divided in the following groups: (1) Sham+V (n=10): Sham-operated males with vehicle used; (2) Sham+N (n=13): Sham-operated males treated with nifedipine (10 mg/kg/day); (3) 2K/1C+V (n=14): 2K/1C-operated males with vehicle used; and (4) 2K/1C+N (n=16): 2K/1C-operated males treated with nifedipine.

RESULTS

The data indicated an association between hypertension induced by the 2K/1C model and reduction of reproductive function, as demonstrated by an impairment of sexual behavior, higher plasma PRL and lower plasma testosterone and FSH. The treatment with nifedipine prevented the reduction of sexual behavior and the increase of plasma PRL, but did not alter the reduction of plasma testosterone and FSH and spermatogenesis of 2K/1C rats.

CONCLUSIONS

Reproductive function is adversely affected in the 2K/1C animal model, and high blood pressure plays a role in the modulation of plasma PRL and sexual behavior. Moreover, other events, without high blood pressure, but with high plasma renin activity associated with the 2K/1C model, contribute directly to the reduction of plasma testosterone and FSH and impaired spermatogenesis.

Antisteroidogenic actions of hydrogen peroxide on rat Leydig cells

It has been well known that reactive oxygen species (ROS) are produced in the steroidogenic pathway and spermatozoa. H2O2, one of ROS produced by spermatozoa, appears to be a primary toxic agent. In the present study, we examined the effects of H2O2 on the basal and evoked-testosterone release from primary Leydig cells, the protein expressions of cytochrome P450 side chain cleavage enzyme (P450scc) and steroidogenic acute regulatory (StAR) protein were also investigated. Our preparation was found to contain approximately 87% Leydig cells and very few macrophages. The results demonstrated that H2O2 (>1 x 10(-4) M) significantly inhibited the basal and hCG-stimulated testosterone release. H2O2 abolished forskolin- or 8-Br-cAMP-evoked testosterone release. In the presence of pregnenolone, progesterone, or androstenedione, the inhibitory effect of H2O2 on testosterone release was prevented. H2O2 also inhibited pregnenolone production in the presence of trilostane (an inhibitor of 3beta-hydroxysteroid dehydrogenase), therefore diminished the activity of P450scc in Leydig cells. In addition to the inhibition of hormone secretion, H2O2 also regulated steroidogenesis by diminishing protein expression of StAR. These results suggest that H2O2 acts directly on rat Leydig cells to diminish testosterone production by inhibiting P450scc activity and StAR protein expression.

Relationship of the hormone-sensitive lipase-mediated modulation of cholesterol metabolism in individual compartments of the testis to serum pituitary hormone and testosterone concentrations in a seasonal breeder, the mink (Mustela vison)

The role of cholesterol differs in the two compartments of the testis. In the interstitial tissue, cholesterol is necessary for the synthesis of testosterone, whereas in the seminiferous tubules, membrane cholesterol content in developing germ cells will influence the gametes' fertility. Here we evaluate the hormone-sensitive lipase (HSL) modulation of the cholesterol metabolism in each compartment of the testis. Two HSL immunoreactive bands of 104- and 108-kDa were detected in Western blots performed with polyclonal anti-human HSL antibodies in the interstitial tissue (ITf)- and seminiferous tubule (STf)-enriched fractions generated from testes harvested at 30-day intervals during puberty and, in the adult mink, during the annual seasonal reproductive cycle. Epididymal spermatozoa expressed a 104-kDa HSL isoform, and HSL was active in these cells. Immunolabeling localized HSL to interstitial macrophages; Sertoli cells, where its distribution was stage specific; spermatids; and the equatorial segment of spermatozoa. Total HSL protein levels, specific enzymatic activity, and free cholesterol (FC):esterified cholesterol (EC) ratios varied concomitantly in STf and ITf and reached maximal values in the adult during the period of maximal spermatogenic activity. In STf, HSL-specific activity correlated with FC:EC ratios but not with triglyceride levels. In STf, high HSL-specific activity occurred concomitantly with high FSH serum levels. In ITf, HSL-specific activity was high during periods of low serum prolactin levels and high serum testosterone levels. The results suggest that 1) modulation of cholesterol metabolism in individual testicular compartments may be regulated by HSL isoforms expressed by distinct cells; 2) interstitial macrophages may be part of a system involved in the synthesis of steroid hormones and in the recycling of sterols in the interstitium, whereas in the tubules, recycling could be ensured by Sertoli cells; 3) there is distinctive substrate preference for testicular HSL; and 4) HSL may be the only cholesterol esterase in this location.

Role of testicular interstitial macrophages in regulating testosterone release in hyperprolactinemia

Hyperprolactinemia-induced hypogonadism has been linked to a dysfunction of the hypothalamus-pituitary-testis axis. The direct inhibitory effects of prolactin on the testicular release of testosterone have also been demonstrated, though their mechanisms remain unclear. Incubation of rat testicular interstitial cells (TICs) with prolactin stimulated the release of testosterone. TICs from rats with anterior pituitary-grafting-induced hyperprolactinemia release lower amounts of testosterone than controls. However, Leydig cells isolated from anterior pituitary-grafted rats release a greater amount of testosterone. These paradoxical observations have remained unexplained. This study examined the roles of testicular interstitial macrophages and of their product, tumor necrosis factor-alpha (TNF-alpha), in regulating Leydig cells under condition of hyperprolactinemia. Hyperprolactinemia was induced by grafting two anterior pituitary glands of rats under the renal capsule. Control animals were grafted with rat cortex tissue. The rats were sacrificed 6 weeks later. TICs and macrophages, and Leydig cells were isolated for in vitro incubation and drugs challenge. Testosterone released by testicular interstitial or Leydig cells was measured by radioimmunoassay. TNF-alpha concentration in the medium of TICs or macrophages was measured by enzyme-linked immunosorbent assay (ELISA). A dose-dependent stimulation of TNF-alpha secretion in the medium of TICs or macrophages by the prolactin challenge was observed. Higher amounts of TNF-alpha were released by TICs in the anterior pituitary-grafted rats than in the control group. In contrast, the release of TNF-alpha by testicular interstitial macrophages isolated from the anterior pituitary- and cortex-grafted groups was quantitatively similar. Challenge with human chorionic gonadotropin did not modify the TNF-alpha release by testicular interstitial macrophages in either group. Challenge of Leydig cells with TNF-alpha inhibited their release of testosterone stimulated by human chorionic gonadotropin, but not their basal testosterone release. These different patterns of testosterone release in TICs versus Leydig cells cultures in anterior pituitary-grafted rats may be due to the influence of testicular interstitial macrophages. These observations correlate with in vivo conditions, where prolactin increases the release of TNF-alpha by testicular interstitial macrophages, which, in turn, decreases the human chorionic gonadotropin-stimulated release of testosterone by Leydig cells. In summary, hyperprolactinemia-induced hypogonadism involves a mechanism of prolactin-originated, macrophage-mediated inhibitory regulation of testosterone release by Leydig cells. TNF-alpha, one of the cytokines secreted by macrophages, may play a key role in this mechanism.

Progesterone attenuates the inhibitory effects of cardiotonic digitalis on pregnenolone production in rat luteal cells

Previous studies have shown that digoxin decreases testosterone secretion in testicular interstitial cells. However, the effect of digoxin on progesterone secretion in luteal cells is unclear. Progesterone is known as an endogenous digoxin-like hormone (EDLH). This study investigates how digitalis affected progesterone production and whether progesterone antagonized the effects of digitalis. Digoxin or digitoxin, but not ouabain, decreased the basal and human chorionic gonadotropin (hCG)-stimulated progesterone secretion as well as the activity of cytochrome P450 side chain cleavage enzyme (P450scc) in luteal cells. 8-Br-cAMP and forskolin did not affect the reduction. Neither the amount of P450scc, the amount of steroidogenic acute regulatory (StAR) protein, nor the activity of 3beta-hydroxysteroid dehydrogenase (3beta-HSD) was affected by digoxin or digitoxin. Moreover, in testicular interstitial and luteal cells, progesterone partially attenuated the reduction of pregnenolone by digoxin or digitoxin and the progesterone antagonist, RU486, blocked this attenuation. These new findings indicated that (1) digoxin or digitoxin inhibited pregnenolone production by decreasing the activity of P450scc enzyme, but not Na(+)-K(+)-ATPase, resulting in a decrease on progesterone secretion in rat luteal cells, and (2) the inhibitory effect on pregnenolone production by digoxin or digitoxin was reversed partially by progesterone. In conclusion, digoxin or digitoxin decreased progesterone production via the inhibition of pregnenolone by decreasing P450scc activity. Progesterone, an EDLH, could antagonize the effects of digoxin or digitoxin in luteal cells.

Hypogonadism in men consuming sustained-action oral opioids

Naturally occurring opiates (endorphins) diminish testosterone levels by inhibiting both hypothalamic gonadotrophin releasing hormone production and testicular testosterone synthesis. Heroin addicts treated with a single daily dose of methadone and nonaddicts receiving continuous intrathecal opioids quickly develop low luteinizing hormone and total testosterone levels. A similar pattern was sought in men consuming commonly prescribed oral opioids. Free testosterone (FT), total testosterone (TT), estradiol (E(2)), dihydrotestosterone (DHT), luteinizing hormone (LH), and follicle-stimulating hormone (FSH) were measured in 54 community-dwelling outpatient men consuming oral sustained-action dosage forms of opioids several times daily for control of nonmalignant pain. Hormone levels were related to the opioid consumed, dosage and dosage form, nonopioid medication use, and several personal characteristics and were compared with the hormone analyses of 27 similar men consuming no opioids. Hormone levels averaged much lower in opioid users than in control subjects in a dose-related pattern (P < .0001 for all comparisons). FT, TT, and E(2) levels were subnormal in 56%, 74%, and 74%, respectively, of opioid consumers. Forty-eight men (89%) exhibited subnormal levels of either FT or E(2). Either TT or E(2) level was subnormal in all 28 men consuming the equivalent of 100 mg of methadone daily and in 19 of 26 (73%) consuming smaller opioid doses. Eighty-seven percent (39 of 45) of opioid-ingesting men who reported normal erectile function before opioid use reported severe erectile dysfunction or diminished libido after beginning their opioid therapy. Commonly prescribed opioids in sustained-action dosage forms usually produce subnormal sex hormone levels, which may contribute to a diminished quality of life for many patients with painful chronic illness.

Progressive prostate hyperplasia in adult prolactin transgenic mice is not dependent on elevated serum androgen levels

BACKGROUND

Transgenic mice overexpressing the rat prolactin (PRL) gene under control of the metallothionein-1 promoter (Mt-1) develop a dramatic prostatic enlargement. These animals also display significantly elevated testosterone serum levels. In this study, we aim to clarify the role of circulating androgen levels in the promotion of abnormal prostate growth in the adult PRL transgenic mouse prostate.

METHODS

Prostate morphology and androgen-receptor distribution patterns were analyzed in castrated and testosterone substituted adult PRL transgenic and in wild-type males.

RESULTS

Progressive prostatic hyperplasia in adult PRL transgenic males was not affected by substitution to serum testosterone levels corresponding to wild-type. Furthermore, prolonged testosterone treatment in adult wild-type males did not produce any significant changes in prostate growth or morphology compared with wild-type controls. Immunohistochemical studies revealed a significantly increased proportion of androgen receptor positive epithelial cells in all lobes of the PRL transgenic prostate versus wild-type.

CONCLUSION

The present study demonstrates that progressive prostate hyperplasia in adult PRL transgenic mice is not dependent on elevated serum androgen levels. Furthermore, prolonged androgen treatment in adult wild-type male mice appears to have no significant effect on prostate growth. In addition, our results suggest that prolonged hyperprolactinemia results in changes in prostate epithelial and stromal cell androgen receptor distribution.

On the occurrence of Leydig cell tumors in the F344 rat

Dunning began inbreeding, what is now the Fischer F344 rat, in 1931. Because of her publications showing a low incidence of spontaneous tumors to 35 months of age, we selected the F344 rat for most of the studies in the National Cancer Institute (NCI) Bioassay Program, beginning in 1964. We were surprised by the finding that untreated male F344 rats displayed a high incidence of Leydig cell tumors of the testes beginning at about 17 months of age. The key difference between the results of Dunning and the NCI Bioassay Program was that her animals were retired breeders, whereas the NCI studies utilized virgin rats. The question of breeding was, therefore, examined as a possible protective factor. Groups of male F344 CDF/Crl rats were kept as virgin animals, or permitted access to bilaterally tube ligated female F344/Crl rats that were replaced twice over a 52-week period. At that time, all males from both groups were housed three per cage to 85 weeks when they were killed in a CO(2) atmosphere and necropsied. Sections were prepared from the fixed tissues, stained and studied by histopathology. The results were evaluated by appropriate statistical methods. Virgin and sexually active F344 rats displayed monolateral or bilateral Leydig cell tumors. There was no statistical difference between the two groups. Despite the early difference between breeding and virgin F344 rats, a control experiment failed to disclose an effect of sexual activity on the occurrence of Leydig cell cancers. This disease displays some difference in incidence in various parts of the world, with the higher socioeconomic groups having a greater incidence. Etiological factors on the occurrence of this disease in animals and in humans remain to be discovered.

Inhibition of testosterone production by propylthiouracil in rat Leydig cells

Propylthiouracil (PTU) is a thioamide drug used clinically to inhibit thyroid hormone production. However, PTU is associated with some side effects in different organs. In the present study, the acute and direct effects of PTU on testosterone production in rat Leydig cells were investigated. Leydig cells were isolated from rat testes, and an investigation was performed on the effects of PTU on basal and evoked-testosterone release, the functions of steroidogenic enzymes, including protein expression of cytochrome P450 side-chain cleavage enzyme (P450(scc)) and mRNA expression of the steroidogenic acute regulatory protein (StAR). Rat Leydig cells were challenged with hCG, forskolin, and 8-bromo-cAMP to stimulate testosterone release. PTU inhibited both basal and evoked-testosterone release. To study the effects of PTU on steroidogenesis, steroidogenic precursor-stimulated testosterone release was examined. PTU inhibited pregnenolone production (i.e., it diminished the function of P450(scc) in Leydig cells). In addition to inhibiting hormone secretion, PTU also regulated steroidogenesis by diminishing mRNA expression of StAR. These results suggest that PTU acts directly on rat Leydig cells to diminish testosterone production by inhibiting P450(scc) function and StAR expression.

Stimulatory effect of lactate on testosterone production by rat Leydig cells

Previously we found that the increased plasma testosterone levels in male rats during exercise partially resulted from a direct and luteinizing hormone (LH)-independent stimulatory effect of lactate on the secretion of testosterone. In the present study, the acute and direct effects of lactate on testosterone production by rat Leydig cells were investigated. Leydig cells from rats were purified by Percoll density gradient centrifugation subsequent to enzymatic isolation of testicular interstitial cells. Purified rat Leydig cells (1 x 10(5) cells/ml) were in vitro incubated with human chorionic gonadotropin (hCG, 0.05 IU/ml), forskolin (an adenylyl cyclase activator, 10(-5) M), or 8-bromo-adenosine-3':5'-cyclic monophosphate (8-Br-cAMP, 10(-4) M), SQ22536 (an adenylyl cyclase inhibitor, 10(-6)-10(-5) M), steroidogenic precursors (25-hydroxy-cholesterol, pregnenolone, progesterone, and androstenedione, 10(-5) M each), nifedipine (a L-type Ca(2+) channel blocker, 10(-5)-10(-4) M), or nimodipine (a potent L-type Ca(2+) channel antagonist, 10(-5)-10(-4) M) in the presence or absence of lactate at 34 degrees C for 1 h. The concentration of medium testosterone was measured by radioimmunoassay. Administration of lactate at 5-20 mM dose-dependently increased the basal testosterone production by 63-187% but did not alter forskolin- and 8-Br-cAMP-stimulated testosterone release in rat Leydig cells. Lactate at 10 mM enhanced the stimulation of testosterone production induced by 25-hydroxy-cholesterol in rat Leydig cells but not other steroidogenic precursors. Lactate (10 mM) affected neither 30- nor 60-min expressions of cytochrome P450 side chain cleavage enzyme (P450scc) and steroidogenic acute regulatory (StAR) protein. The lactate-stimulated testosterone production was decreased by administration of nifedipine or nimodipine. These results suggested that the physiological level of lactate stimulated testosterone production in rat Leydig cells through a mechanism involving the increased activities of adenylyl cyclase, cytochrome P450scc, and L-type Ca(2+) channel.