Stress-induced synthesis of melatonin: possible involvement of the endogenous monoamine oxidase inhibitor (tribulin).

Cold-restrained stress increased rat pineal melatonin and N-acetylserotonin content. This effect was partially prevented by lorazepam. Serotonergic turnover (ratio of 5-hydroxyindole acetic acid to serotonin) was significantly decreased in stressed but not in stressed rats pretreated with lorazepam, suggesting stress-induced inhibition of monoamine oxidase (MAO). Literature data indicate that the same type of stress increases the production of the endogenous MAO inhibitor. The implication of stress-induced MAO inhibition on melatonin synthesis in anxiety and drug withdrawal is discussed.