Effects of cycloheximide and aminophylline on 5-methoxytryptophol and melatonin contents in the chick pineal gland

The chick pineal gland rhythmically synthesizes two 5-methoxyindoles, melat onin and 5-methoxytryptophol. These rhythms are circadian in nature and hav e opposite phases. The aim of this study nas to determine the effects of cy cloheximide, a protein synthesis inhibitor, and aminophylline, an inhibitor of phosphodiesterase, on 5-methoxytryptophol content in the chick pineal g land and to compare this with the drugs' action on pineal melatonin product ion. Inhibition of melatonin biosynthesis by cycloheximide (I mg/kg, i.p.), revealed by a marked reduction in the nighttime activity of serotonin N-ac etyltransferase (AA-NAT; a key regulatory enzyme in melatonin synthesis) an d melatonin concentrations, was accompanied by a significant increase in 5- methoxytryptophol content. In contrast, administration of aminophylline (10 0 mg/kg, i.p.) to light-exposed chicks significantly increased pineal AA-NA T activity and melatonin levels and decreased 5-methoxytryptophol concentra tions. It is concluded that in the chick the production of pineal 5-methoxy tryptophol and melatonin is inversely correlated, (C) 2000 Academic Press.