A novel mechanism for the melatonin inhibition of testosterone secretion by rat Leydig cells: reduction of GnRH-induced increase in cytosolic Ca2+

Abstract

The site of inhibition, by melatonin, of GnRHdependent testosterone secretion was investigated in adult rat Leydig cells cultured in vitro. The various effects downstream of the binding of GnRH to its own receptor were isolated and mimicked by specific drugs. Testosterone secretion was then evaluated after 3 h stimulation with GnRH, thapsigargin (1 µM), phorbol-12-myristate-13-acetate (100 nM), arachidonic acid (20 µM), and ionomycin (1 µM) in the presence or absence of melatonin (215 nM). The effect of melatonin on the GnRH-induced changes in cytoplasmic calcium concentration ([Ca 2+ ] i ) was also studied, using Fura-2 as fluorescent Ca 2+ indicator. Melatonin attenuated the increase in [Ca 2+ ] i and inhibited the testosterone secretion induced by GnRH, but not that induced by ionomycin. Both ionomycin and thapsigargin potentiated GnRH-induced testosterone secretion; however, ionomycin, but not thapsigargin, partially prevented the inhibitory effect of melatonin on cells stimulated with GnRH. The effect of melatonin was probably dependent on the binding of melatonin to its Gi-protein-coupled receptor, as the inhibitory effect on GnRH-induced secretion was supressed in cells pretreated with pertussis toxin in a concentration of 180 ng/ml for 20 h. Assay of 17-hydroxy-progesterone showed that, irrespective of the treatment, cells cultured with melatonin secreted greater amounts than controls. We conclude that melatonin reduces GnRH-induced testosterone secretion by 1) decreasing [Ca 2+ ] i , through impairment of the GnRH-dependent release of Ca 2+ from intracellular stores and 2) blocking 17-20 desmolase enzymatic activity, an effect that occurs irrespective of changes in [Ca 2+ ] i .

Maternal melatonin selectively inhibits cortisol production in the primate fetal adrenal gland

“…Since we observed no changes in DHAS production, minor compensatory adjustments at steps in the synthesis of DHAS involving Steroidogenic Acute Regulatory protein (StAR), or the enzymes cholesterol side‐chain cleavage cytochrome P450 (P450scc) and cytochrome P450 17‐hydroxylase (P450c17) may have occurred. This possibility needs to be investigated, given that melatonin decreases human chorionic gonadotropin (HCG)‐stimulated mitochondrial StAR in a line of Leydig cells (Wu et al 2001) and results in accumulation of 17‐OH progesterone in gonadotropin releasing hormone (GnRH)‐stimulated rat Leydig cell cultures (Valenti et al 1999).…”

Melatonin as a Biomarker of Circadian Dysregulation

“…Animal studies indicate that melatonin can modify the firing frequency of the hypothalamic gonadotropin-releasing hormone pulse generator, thereby affecting the release of gonadotropins (luteinizing hormone and follicle-stimulating hormone) from the pituitary (10-13) and stimulating testicular testosterone or ovarian estrogen production and release (14,15). Animal studies have also shown that melatonin can inhibit luteinizing hormone-induced testosterone production in rats (16)(17)(18), inhibits prolactin cell activity in male and female hamsters (19), and suppresses several aspects of reproductive physiology in male hamsters (20). Human studies indicate that decreased concentrations of circulating melatonin (such as those brought about by circadian disruption) can result in increased release of the gonadotropins luteinizing hormone and follicle-stimulating hormone from the pituitary and estrogen release by the ovaries (21)(22)(23)(24)(25).…”

Physiological Effects Of Melatonin on Leptin, Testosterone and Biochemical Parameters in Albino Rats

“…Moreover, Valenti et al, (1999) concluded that MEL reduces gonadotropin releasing hormone(GnRH)-induced testosterone secretion by decreasing cytoplasmic calcium concentration, through impairment of the GnRH-dependent release of calcium from intracellular stores and blocking 17-20 desmolase enzymatic activity, an effect that occurs irrespective of changes in calcium concentration.…”