Long-term melatonin administration does not alter pituitary-gonadal hormone secretion in normal men

The role of melatonin in the regulation of reproduction in humans is still controversial. In the present study the effects of melatonin were examined, 6 mg given orally every day at 1700 h for 1 month in a double-blind, place bo controlled fashion, on the nocturnal secretory profiles of luteinizing h ormone (LH), follicle stimulating hormone (FSH)1 testosterone and inhibin b eta in six healthy adult men. Serum concentrations of LH, FSH, testosterone and inhibin beta were determined before and after treatment every 15 min f rom 1900 to 0700 h over 3 nights in a controlled dark-light environment wit h simultaneous polysomnographic sleep recordings. The following sleep param eters were determined: total recording time, sleep latency, actual sleep ti me, sleep efficiency, rapid eye movement (REM) sleep latency and percentage s of sleep stages 2, 3/4 and REM. There were no statistically significant d ifferences in all sleep parameters between baseline and placebo or between baseline and melatonin except for longer REM latency and Ion er percentage REM at baseline than under melatonin treatment. These are explained as refl ecting first-night effect at baseline, The mean nocturnal LH, FSH, testoste rone and inhibin beta integrated nocturnal secretion values did not change during the treatment period. Likewise, their pulsatile characteristics duri ng melatonin treatment mere not different from baseline values, Taken toget her, these data suggest that long-term melatonin administration does not al ter the secretory patterns of reproductive hormones in normal men.