Melatonin does not alter human serum gondotropin and testosterone levels, but it increases prolactin levels

Abstract

Administration of the pineal hormone melatonin (MEL) lowers serum gonadotropin (GN) levels, delays sexual maturation and elicits gonadal atrophy in rodents. In humans an antigonadotropic effect of the pineal has been sought for many years. Recently we reported higher nocturnal serum MEL levels in prepubertal children than in young adults. Now we have examined the immediate effects of exogenous MEL on basal levels of various hormones. After giving informed consent 5 healthy, male adolescents received 80 mg oral MEL at 11:00; 3 volunteers received the same dosis at 11:00,12:00 and 13:00. Serum concentrations of MEL, GN, testosterone (T) and prolactin (PRL) were determined at 30-min. intervals several hours prior to, during, and after MEL administration. Though serum MEL concentrations increased at least 1000 times above basal levels GN and T were not altered. PRL rose from 4.6±0.7 (x±SEM) to 7.6±0.9 ng/ml (p<0.005) after MEL application. To examine the effect of the pineal hormone on the pulsatile secretion patterns of GN and PRL, in 2 adolescents sera were taken at 10-min. intervals for 6 hours before and after MEL treatment. The pulstile secretion pattern of GN was not altered by MEL; again, PRL levels were higher after MEL than before. Thus, a single dosis of MEL does not affect serum GN levels in humans, but it increases PRL serum concentrations.