Contemporaneous melatonin administration modifies the circadian
response to nocturnal bright light stimuli.
Cagnacci, Angelo, Renza Soldani, Samuel Sc Yen.
Department of Reproductive Medicine, University of California San
Diego, 9500 Gilman Drive, La Jolla, CA 92093-0633, Mellon Foundation
Research Fellow, Reproductive Endocrinology Fellow, Clayton
Foundation Investigator
APStracts 3:0314R, 1996.
We investigated whether the contemporaneous administration of
melatonin can modify circadian phase shifts induced by bright light
stimuli. After a baseline evaluation, ten women were exposed for
three consecutive nights, to a 4-h bright light stimulus (>3000
lux) initiated at the time of the estimated core body temperature
(BTc) 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 re-evaluated at the end of treatment.
Bright light phase advanced, of about 90-120 min, BTc (p<0.01),
cortisol (p<0.05), and melatonin (p<0.01) rhythms.
Contemporaneous administration of melatonin antagonised the phase
advances of the cortisol and BTc rhythms, as well as of 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.
Received 28 March 1996; accepted in final form 29 July 1996.
APS Manuscript Number R183-6.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 29 August 1996