THE AMPLITUDE OF ENDOGENOUS MELATONIN PRODUCTION IS NOT AFFECTED BY MELATONIN TREATMENT IN HUMANS

A physiological dose of melatonin (0.5 mg) or placebo was given at bed time to night shift workers (n=21) for seven days, and endogenous mela tonin profiles were measured on the eighth day. The amplitude of endog enous melatonin secretion was unchanged by treatment. Also, a melatoni n treatment trial using a 50 mg daily bedtime dose for 37 days to a bl ind subject resulted in no change in the endogenous melatonin profile. We conclude that circulating melatonin can shift the phase, but does not alter the amplitude, of pineal melatonin secretion.