Early effects of hCG on human testicular cyclic AMP content, protein kinase activity, in-vitro progesterone conversion and the serum concentrations of testosterone and oestradiol

The in vivo and in vitro stimulatory effects of cordycepin on mouse leydig cell steroidogenesis

Cordycepin, a pure compound of Cordyceps sinensis (CS), is known as an adenosine analog. We have found that CS stimulated Leydig cell steroidogenesis. Here we investigated the in vivo and in vitro effects of cordycepin in primary mouse Leydig cell steroidogenesis. The results indicate that cordycepin increased the plasma testosterone concentration. Cordycepin also stimulated in vitro mouse Leydig cell testosterone production in dose- and time-dependent manners. We further observed that cordycepin regulated the mRNA expression of the A1, A2a, A2b, and A3 adenosine receptors in the mouse Leydig cells, and that antagonists of A1, A2a, and A3 suppressed testosterone production 20-50% testosterone production. Furthermore, Rp-cAMPS (cAMP antagonist) and Protein Kinase A (PKA) inhibitors (H89 and PKI) significantly decreased cordycepin-induced testosterone production, indicating that the PKA-cAMP signal pathway was activated by cordycepin through adenosine receptors. Moreover, cordycepin induced StAR protein expression, and H89 suppressed cordycepin-induced steroidogenic acute regulatory (StAR) protein expression. Conclusively, cordycepin associated with adenosine receptors to activate cAMP-PKA-StAR pathway and steroidogenesis in the mouse Leydig cells.

Adrenomedullin Peptide: Gene Expression of Adrenomedullin, its Receptors and Receptor Activity Modifying Proteins, and Receptor Binding in Rat Testis—Actions on Testosterone Secretion1

Adrenomedullin (ADM) has been shown to be present in the human and rat male reproductive systems. This study demonstrates the expression of ADM in the rat testis and its effect on the secretion of testosterone. Whole testicular extracts had 5.43 +/- 0.42 fmol of immunoreactive ADM per milligram of protein and 84 +/- 8 fg of ADM mRNA per picogram of Actb (beta-actin) mRNA. Immunocytochemical studies showed positive ADM immunostaining in the Leydig cells and in the Sertoli cells. Gel filtration chromatography of testicular extracts showed two peaks, with the predominant one eluting at the position of the ADM precursor. Furthermore, the testis was shown to coexpress mRNAs encoding the calcitonin receptor-like receptor and receptor activity modifying protein 1 (Ramp1), Ramp2, and Ramp3. These account for the specific binding of ADM to the testis, which was partially inhibited by human ADM (22-52) and by human calcitonin gene-related peptide (8-37), the ADM and calcitonin gene-related peptide receptor antagonists, respectively. Administration of ADM to testicular blocks in vitro resulted in a dose-dependent inhibition of hCG-stimulated release of testosterone, which was abolished by the administration of ADM (22-52). Our results suggest a paracrine effect of ADM on testicular steroidogenesis.

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.

Direct effects of propylthiouracil on testosterone secretion in rat testicular interstitial cells

The aim of this study was to investigate the mechanism by which propylthiouracil (PTU) exerts its inhibitory effects on the production of testosterone by rat testicular interstitial cells. The plasma testosterone concentration was decreased 60 and 120 min after an intravenous infusion of PTU (10 or 20 mg kg(-1)), but the concentration of plasma T(4) was unaffected by the drug treatment. Exposure of anterior pituitary tissue to PTU (3-12 mM) in vitro did not affect either basal or gonadotropin-releasing hormone (GnRH)-stimulated luteinizing hormone (LH) release. PTU (3 - 12 mM) inhibited both the basal and the human chorionic gonadotropin (hCG, 0.05 i.u. ml(-1))-stimulated release of testosterone from rat testicular tissue in vitro; at the highest concentration tested (12 mM), it also inhibited the forskolin or 8-bromo-adenosine 3':5'-cyclic monophosphate (8-Br-cyclic AMP)-stimulated release of testosterone. The 25-OH-cholesterol (10(-7)-10(-5) M)-stimulated release of pregnenolone and testosterone by the testicular interstitial cells was inhibited by PTU (12 mM, P<0.05). The results suggest that the inhibitory actions of PTU on testosterone secretion are exerted, at least in part, at the testicular level through a mechanism which is independent of thyroid status and which involves a reduction in P450scc activity and, hence, in the conversion of cholesterol to pregnenolone.

Effects of evodiamine on the secretion of testosterone in rat testicular interstitial cells

Evodiamine, a bioactive component isolated from the Chinese medicine Wu-chu-yu, exhibits vasodilative and antianoxic action. Although evodiamine indeed has many biological effects, its effects on the endocrine system are not clear. The present study explored the effects of evodiamine on testosterone secretion in vitro. Rat collagenase-dispersed testicular interstitial cells (TICs) were incubated with evodiamine (0 to 10(-4) mol/L) in the presence or absence of human chorionic gonadotropin (hCG), forskolin, 8-bromo-adenosine 3':5'-cyclic monophosphate (8-Br-cAMP), or steroidogenic precursors (including 25-hydroxycholesterol, pregnenolone, progesterone, 17alpha-hydroxyprogesterone, and androstenedione) at 34 degrees C for 1 hour. The testosterone concentration in the media samples was measured by radioimmunoassay. Evodiamine 10(-4) mol/L was effective to reduce both basal and hCG-stimulated testosterone secretion in rat TICs after 1, 2, or 4 hours of incubation. The stimulatory effect of forskolin on testosterone release in TICs was prevented by administration of evodiamine. Evodiamine 10(-4) mol/L also decreased 8-Br-cAMP- and androstenedione-stimulated testosterone secretion. These results suggest that evodiamine reduces testosterone secretion in rat TICs via a mechanism involving reduced activity of cAMP-related pathways and 17beta-hydroxysteroid dehydrogenase (17beta-HSD).

Inhibitory effect of digoxin on testosterone secretion through mechanisms involving decreases of cyclic AMP production and cytochrome P450scc activity in rat testicular interstitial cells

1. In vivo and in vitro experiments were performed to examine inhibitory effects of digoxin on testosterone secretion and to determine possible underlying mechanisms. 2. A single intravenous injection of digoxin (1 microg kg(-1)) decreased the basal and human chorionic gonadotropin (hCG)-stimulated plasma testosterone concentrations in adult male rats. 3. Digoxin (10(-7) - 10(-4) M) decreased the basal and hCG-stimulated release of testosterone from rat testicular interstitial cells in vitro. 4. Digoxin (10(-7) - 10(-4) M) also diminished the basal and hCG-stimulated production of cyclic 3':5'-adenosine monophosphate (AMP) and attenuated the stimulatory effects of forskolin and 8-Br-cyclic AMP on testosterone production by rat testicular interstitial cells. 5. Digoxin (10(-4) M) inhibited cytochrome P450 side chain cleavage enzyme (cytochrome P450sec) activity (conversion of 25-hydroxy cholesterol to pregnenolone) in the testicular interstitial cells but did not influence the activity of other steroidogenic enzymes. 6. These results suggest that digoxin inhibits the production of testosterone in rat testicular interstitial cells, at least in part, via attenuation of the activities of adenylyl cyclase and cytochrome P450sec.

The role of cyclic AMP production, calcium channel activation and enzyme activities in the inhibition of testosterone secretion by amphetamine

1. The aim of this study was to investigate the mechanism by which amphetamine exerts its inhibitory effect on testicular interstitial cells of male rats. 2. Administration of amphetamine (10(-12)-10(-6) M) in vitro resulted in a dose-dependent inhibition of both basal and human chorionic gonadotropin (hCG, 0.05 iu ml(-1))-stimulated release of testosterone. 3. Amphetamine (10(-9) M) enhanced the basal and hCG-increased levels of adenosine 3':5'-cyclic monophosphate (cyclic AMP) accumulation in vitro (P<0.05) in rat testicular interstitial cells. 4. Administration of SQ22536, an adenylyl cyclase inhibitor, decreased the basal release (P<0.05) of testosterone in vitro and abolished the inhibitory effect of amphetamine. 5. Nifedipine (10(-6) M) alone decreased the secretion of testosterone (P<0.01) but it failed to modify the inhibitory action of amphetamine (10(-10)-10(-6) M). 6. Amphetamine (10(-10)-10(-6) M) significantly (P<0.05 or P<0.01) decreased the activities of 3beta-hydroxysteroid dehydrogenase (3beta-HSD), P450c17, and 17-ketosteroid reductase (17-KSR) as indicated by thin-layer chromatography. (t.l.c.). 7. These results suggest that increased cyclic AMP production, decreased Ca2+ channel activity and decreased activities of 3beta-HSD, P450c17, and 17-KSR are involved in the inhibition of testosterone production induced by the administration of amphetamine.

Lactate and the effects of exercise on testosterone secretion: evidence for the involvement of a cAMP-mediated mechanism

The effects of swimming and lactate on the release of testosterone were examined in male rats. During in vivo experiments, male rats were catheterized via the right jugular vein and blood was collected at 0, 10, 15, 30, and 60 min following the exercise, or they were catheterized via the right jugular vein and the left femoral vein and blood was collected at 0, 2, 5, 10, 15, 30, 60, and 120 min after a 10-min infusion at lactate (13 mg.kg-1.min-1). Trunk blood and blood from the testicular vein were also collected after 10 min of swimming or water immersion. In an in vitro experiment, testicular fragments were challenged with lactate (0.01-10 mM) and/or human chorionic gonadotropin (hCG; 0.5 IU.mL-1), and the mediobasal hypothalamus (MBH) was challenged with lactate (8 mM). The post-exercise levels of plasma lactate and testosterone at 10, 15, and 30 min were higher than resting levels. Plasma luteinizing hormone (LH) was increased following 30 min of swimming. Administration of lactate or hCG increased in a dose dependent manner testicular cyclic adenosine 3':5' monophosphate (cAMP) and testosterone release. Plasma testosterone increased after swimming and lactate infusion. Incubation of MBH with lactate increased the gonadotropin-releasing hormone (GnRH) level in the medium. These results suggest that the increased plasma testosterone levels in male rats during exercise is at least partially a result of a direct and LH-independent stimulatory effect of lactate on the secretion of testosterone by increasing testicular cAMP production. Swim-elevated plasma LH may be a result of a rise of GnRH caused by lactate.

Lactate stimulates progesterone secretion via an increase in cAMP production in exercised female rats

The effect of exercise on the production of ovarian progesterone was examined in female rats. During in vivo experiments, diestrous rats were catheterized via the right jugular vein (RJV), and blood samples were collected before and after 10, 15, 30, and 60 min of swimming. In addition, blood samples were collected from the RJV before and 2, 5, 10, 15, 30, 60, and 120 min after 10 min of infusion of lactate (13 mg.kg-1.min-1) through the left femoral vein. To explore if lactate modulates progesterone secretion by acting directly on rat ovary or on anterior pituitary gland (AP), an in vitro experiment that mimicked the in vivo condition was performed. The ovarian tissue was challenged with lactate (0.01-10 mM) or porcine follicle-stimulating hormone (1 microgram/ml) and 3-isobutyl-1-methylxanthine (1 mM) for 60 min, and the AP was challenged with lactate ranging from 0.1 to 10 mM or 10 nM gonadotropin-releasing hormone for 30 min. The postexercise levels of plasma glucose, lactate, and progesterone at 10, 15, and 30 min were significantly higher than the corresponding basal levels. Plasma luteinizing hormone (LH) did not change after exercise. An elevation of plasma lactate and progesterone was found at 15 and 30 min subsequent to 10 min of infusion of lactate. Lactate ranging from 0.01 to 10 mM significantly increased ovarian adenosine 3',5'-cyclic monophosphate (cAMP) and progesterone production in a dose-dependent manner. LH concentration in plasma was not changed subsequent to lactate infusion. LH level in media samples was not altered after incubation of AP with lactate. These results suggest that the increase of plasma progesterone level in rats during exercise is independent of LH secretion and at least in part is due directly to a stimulatory effect of lactate on the production of ovarian cAMP.

Inhibition by amphetamine of testosterone secretion through a mechanism involving an increase of cyclic AMP production in rat testes

1. The effect of amphetamine on the secretion of testosterone and the production of testicular adenosine 3':5'-cyclic monophosphate (cyclic AMP) in rats was studied. 2. A single intravenous injection of amphetamine decreased the basal and human chorionic gonadotropin (hCG)-stimulated levels of plasma testosterone. Plasma LH levels were not altered by the injection of amphetamine. 3. Administration of amphetamine in vitro resulted in a dose-dependent inhibition of both basal and hCG-stimulated release of testosterone. 4. Amphetamine enhanced the basal and hCG-increased levels of cyclic AMP accumulation in vitro in rat testes. 5. These results suggest that amphetamine inhibits the spontaneous and hCG-stimulated secretion of testosterone from the testes through a mechanism involving an increase in cyclic AMP production.

Steroidogenesis in the two enriched-Leydig cell populations of human testis: evidence for a positive control by seminiferous tubules secreted factor(s)

In two different enriched populations of Leydig cells (called FI and FII) obtained from human testes (young patients: mean age 36 +/- 3 years, n = 6; aged men: mean age 73 +/- 2 years, n = 5), the dehydroepiandrosterone and testosterone in vitro outputs were increased in a dose- and time-related manners by hCG. Similar results were obtained when the Leydig cells were incubated in presence of either dbcAMP or 22R-hydroxycholesterol. In presence of either hCG or dbcAMP, the coefficient of stimulation (in terms of steroid outputs) was higher in FII when compared to FI. Conversely, the basal production of steroids was greater in FI than in FII, mainly for testosterone. The addition of increasing amounts of seminiferous tubule culture medium (STM) to the Leydig cell incubation medium led to a dose-related enhancement of the steroid production in both enriched-Leydig cell fractions under basal and hCG-stimulated conditions. Similar results were obtained in presence of increased seminiferous tubules length. Additional experiments realized with either concentrated STM or the coculture of seminiferous tubules with purified Leydig cells have confirmed the existence of a paracrine control of Leydig cell steroidogenesis by seminiferous secreted factor(s). A paracrine factor (or factors) from seminiferous tubular origin influences positively and with a high efficiency the Leydig cell function in humans, whatever the age.

Calcitonin inhibits testosterone and luteinizing hormone secretion through a mechanism involving an increase in cAMP production in rats

Effects of calcitonin peptides, including human calcitonin (hCT), salmon calcitonin (sCT), and calcitonin gene-related peptide (CGRP), on the secretion of testosterone and luteinizing hormone (LH) in male rats were studied. Male rats were injected intravenously with human chorionic gonadotropin (hCG), calcitonin peptides, or hCG plus calcitonin peptides. Blood samples were collected at several intervals following hormone challenge. In an in vitro experiment, testis blocks were incubated with hCG (0, 0.05, 0.5, or 5 IU/ml) or hCG (0.5 IU/ml) plus calcitonin peptides (0-10(-9) or 10(-6) M) at 34 degrees C for 30 minutes. Both medium and plasma samples were extracted by ether and analyzed for testosterone by radioimmunoassay (RIA). The concentration of calcium in each plasma sample was measured by an automatic calcium analyzer. The anterior pituitary gland (AP) was incubated with or without calcitonin peptides (0-10 nM) at 37 degrees C for 30 minutes. They were then incubated with gonadotropin releasing hormone (GnRH, 10 nM) for a further 30 minutes. The concentration of LH in AP medium was measured by RIA. The accumulation of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) in both testicular tissues and APs were measured by RIA. A single intravenous injection of calcitonin peptides decreased the basal and hCG-stimulated levels of plasma testosterone gradually from 60 to 180 or 360 minutes after challenge. The plasma calcium was not altered by the injection of calcitonin peptides and/or hCG. Administration of calcitonin peptides in vitro resulted in a dose-dependent inhibition of both basal and hCG-stimulated release of testosterone.(ABSTRACT TRUNCATED AT 250 WORDS)