Melatonin, used as a parapharmaceutic agent to prevent aging processes, attracts increasingly growing attention. Therefore, we have decided to evaluate the influence of pineal hormones on hepatic metabolism. The rats were given melatonin or serotonin for 14 days. Then the activities of P-450-dependent monooxygenase system and b5, cytochrome were evaluated in the hepatic microsomal fraction. It has been shown that serotonin and melatonin decrease both the contents of P-450 cytochrome and b5 cytochrome and the activities of their reductases.

Keywords: cytochrome P-450, Melatonin, Serotonin, hepatic metabolism