5-Methoxypsoralen as a specific stimulating agent of melatonin secretion in humans.

The endocrine effects of the linear furocoumarin, 5-methoxypsoralen (Bergapten), were investigated in 11 normal adults according to a cross-over design with 2 conditions: a 1-week trial with 5-methoxypsoralen (5MOP) administered daily (40 mg/orally) at 0900 h, and after a 1-week period of washout, a similar 1-week trial with daily administrations of 5MOP at 2100 h. The subjects were living under normal nychtohemeral conditions. The plasma levels of melatonin, cortisol, TSH, PRL, and GH were evaluated by hourly blood samples over 24-h periods on the preceding day and on the last day of each condition. Our main finding is that 5MOP specifically stimulates melatonin secretion in humans, with a pronounced effect when administered during the dark phase of the day (at 2100 h). The other endocrine rhythms were unaffected by 5MOP administration. Melatonin has been shown to interact with the regulation of the human circadian system; this specific stimulation may, therefore, be of great interest in disorders associated with abnormalities of circadian rhythms.