Razi Journal of Medical Sciences

Living organisms have multiple biological rhythms. Some of these rhythms are endogenous and some are under the influence of light and dati cydes during 24-hours. Nowadays periodic changes in melatonin secretion from pineal gland and changes in N-acetyl transferase (NAT) activity which influence the melatonin secretion rate has been acknowledged as a basic rhythm. In this study NAT activity in pineal gland of rats during the night in which the rate of melatonin synthesis reaches a maximum has been investigated. According to the techniques employed in the experiments it has become evident that NA T activity depends on the length of light exposure in the environment and, variations of environmental light, considerably changes pineal gland NAT activity by sympathetic innervation via norepinephrine release.