Melatonin inhibits luteinizing hormone releasing hormone (LHRH) induction of LH release from fetal rat pituitary cells.

The in vitro effect of melatonin on the release of luteinizing hormone (LH) and follicle stimulating hormone (FSH) from fetal rat pituitary cells was investigated. A significant inhibition of LH release induced by 10(-9) M luteinizing hormone releasing hormone (LHRH) was seen when cells were incubated with 10(-9) M melatonin. FSH release was unaffected by either LHRH alone or LHRH in combination with melatonin. In addition, the significant inhibitory effect of melatonin was reduced by pretreatment of the pituitary cells with 10(-10) M melatonin. These findings indicate that melatonin can act directly on the fetal pituitary gland to suppress LHRH-induced release of LH perhaps by a mechanism which eventually involves down-regulation of the melatonin receptors.