Effects of long-term light, darkness and oral administration of melatonin on serum levels of melatonin

BACKGROUND: Continuous light or darkness has various effects on different systems. In the present research work, the effects of constant light and darkness exposure of male rats and oral administration of exogenous melatonin on the serum levels of melatonin have been studied. METHODS: Thirty adult male Wistar rats were divided into six groups of: (1) Control, (2) melatonin, (3) light, (4) light and melatonin, (5) darkness, and (6) darkness and melatonin. All groups were placed according to light conditions for 10 days. Melatonin was administered orally after a period of 10 days to Groups 2, 4, and 6 (10 mg/kg of body weight). Serum levels of melatonin were measured using ELISA. RESULTS: The results showed the significant difference on serum melatonin in darkness, no light, and control groups. Although serum levels of melatonin were different in melatonin groups, the difference is not significant. CONCLUSIONS: We concluded that being exposed to continuous darkness leads to an increase in serum melatonin.