title: Contemporaneous melatonin administration modifies the circadian response to nocturnal bright light stimuli.
abstract: We investigated whether the contemporaneous administration of melatonin can modify circadian phase shifts induced by bright light stimuli. After a baseline evaluation, 10 women were exposed for three consecutive nights to a 4-h bright light stimulus (>3,000 lx) initiated at the time of the estimated core body temperature (BT(c)) nadir. Along with light, each woman orally received, randomly and in a double-blind fashion, placebo (n = 5) or melatonin (n = 5; 1 mg 30 min before and 0.75 mg 120 min after the start of light exposure). Daily rhythms were reevaluated at the end of treatment. Bright light phase advanced, by about 90-120 min, BT(c) (P < 0.01), cortisol (P < 0.05), and melatonin (P < 0.01) rhythms. Contemporaneous administration of melatonin antagonized the phase advances of the cortisol and BT(c) rhythms, as well as the melatonin peak and melatonin offset. The phase advance of the melatonin onset was instead enhanced (P < 0.05). Contemporaneous melatonin administration modifies the capability of light to induce circadian phase shifts.
authors.affiliation: Department of Reproductive Medicine, University of California San Diego, La Jolla 92093-0633, USA.
authors.forename: A
authors.initials: A
authors.lastname: Cagnacci
authors.forename: R
authors.initials: R
authors.lastname: Soldani
authors.forename: S S
authors.initials: SS
authors.lastname: Yen
mesh_terms: D000328:Adult; D001831:Body Temperature / Q000187:drug effects / Q000528:radiation effects; D002940:Circadian Rhythm / Q000187:drug effects* / Q000528:radiation effects*; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D006854:Hydrocortisone / Q000097:blood; D008027:Light; D008550:Melatonin / Q000008:administration & dosage* / Q000378:metabolism / Q000494:pharmacology; D010507:Periodicity; D012890:Sleep / Q000187:drug effects / Q000528:radiation effects; D013997:Time Factors
chemical_list: D008550:Melatonin; D006854:Hydrocortisone