5-Methoxypsoralen increases the plasma melatonin levels in humans

Abstract

The aim of this study was to evaluate the acute effects of 5-methoxypsoralen (5-MOP) on the melatonin secretion in humans. Eleven normal volunteers were investigated before (drug-free) and after 6-day periods of treatment with oral 5-MOP, first administered daily at 9 A.M. and after a 1-week free interval administered daily at 9 P.M. Under nyctemeral conditions, the plasma melatonin levels were evaluated over a 24-h period in each session by hourly blood samples and radioimmunoassay. The sensitivity of the retina to light was also evaluated by means of electro-retinography performed at 11 A.M. before and after a morning administration of 5-MOP. Plasma levels of melatonin were significantly increased from the second hour after 5-MOP administration. The hourly mean levels were significantly higher after 5-MOP administration compared to baseline values. This increased secretion was more pronounced after evening than after morning administration. Also, 5-MOP increases the sensitivity of the retina to light under photopic conditions and in the early stages of the dark adaptation period, as observed under scotopic conditions. © 1987.