Exogenous melatonin enhances luteinizing hormone levels of women in the follicular but not in the luteal menstrual phase.

To investigate the effect of exogenous melatonin on LH pulsatility in women during the follicular and luteal menstrual phases.Randomized, double-blind placebo-controlled study.Normal cycling young women (25 to 35 years old).Each subject was admitted at the Clinical Research Center for 2 consecutive days on both the follicular and the luteal menstrual phases. On each day, at 7:00 A.M. an indwelling catether was placed in an antecubital vein for a 10 minutes blood sampling from 9:00 A.M. to 5:00 P.M. On the 2 consecutive days of both the follicular and the luteal menstrual phases, each subject randomly received either placebo or melatonin pills (1 mg at 8:00 and 0.75 mg at 10:00 and 12:00 A.M.).Luteinizing hormone pulsatility.The amplitude of LH pulses and mean LH levels were increased by melatonin in the follicular but not in the luteal menstrual phase.The stimulatory effect of exogenous melatonin on LH is modulated by the endocrine environment and selectively exerted in the follicular phase of the menstrual cycle.