8-methoxypsoralen increases daytime plasma melatonin levels in humans through inhibition of metabolism

• Published in: Photochemistry and photobiology Vol. 60; no. 5; p. 475
• Main Authors: Garde, E, Micic, S, Knudsen, K, Angelo, H R, Wulf, H C
• Format: Journal Article
• Language: English
• Published: United States 01.11.1994
• Subjects: Adult; Animals; Antimetabolites - therapeutic use; Female; Humans; Male; Melatonin - analogs & derivatives; Melatonin - blood; Melatonin - metabolism; Methoxsalen - therapeutic use; Middle Aged; PUVA Therapy; Rats; Skin Diseases - blood; Skin Diseases - drug therapy
• ISSN: 0031-8655
• DOI: 10.1111/j.1751-1097.1994.tb05137.x

It is well established that in healthy humans oral intake of 5- or 8-methoxypsoralen (5- and 8-MOP) is followed by a significant increase in plasma melatonin concentrations. The effect of psoralen on rat melatonin has been studied in vitro and in vivo and a stimulation of release or secretion from the pineal gland has been suggested. In this study we examined the time-related changes in plasma concentrations of 8-MOP, melatonin and 6-sulfatoxymelatonin in 15 patients admitted for routine psoralen plus UVA therapy. On the first day of treatment blood samples were collected before, and 30, 60, 66 and 90 min after intake of 8-MOP (0.6 mg/kg). Although the rate of 8-MOP absorption varied greatly, a significant increase (P = 0.0002) in melatonin levels was found 60 min after 8-MOP intake. During UVA exposure a strongly correlated decrease in mean melatonin and mean 8-MOP concentrations was found, indicating an effect of UVA radiation, either direct or 8-MOP mediated, on circulating melatonin levels. Plasma 6-sulfatoxymelatonin concentrations decreased significantly between all time points, suggesting inhibition of melatonin metabolism.