[Effect of light regimens and melatonin on the homeostasis, life span and development of spontaneous tumors in female rats].

Effect of different light regimens (standard--12 hours of light/12 hours of darkness, natural lightning of the North-West of Russia and constant illumination) and melatonin on the homeostasis, life span parameters and spontaneous tumor development of female rats was studied. Animals at conditions of constant or natural light regimens revealed accelerated aging of organism, decrease of mean (by 13.5% and 25.5% accordingly) and the maximal life span (by 9 and 7 months, accordingly) and faster spontaneous tumor development as compared with the animals kept at the standard light regimen. Melatonin given in nocturnal drinking water (10 mg/l) prevented the adverse effect of the natural light regimen on the homeostasis, life span and tumor development. Melatonin also decreased spontaneous tumor development, first of all, mammary and uterine neoplasm, in the rats kept at the constant illumination.