Rapid Nocturnal Increase in Ovine Pineal N‐Acetyltransferase Activity and Melatonin Synthesis: Effects of Cycloheximide

Abstract

Thirty minutes after the onset of darkness, ovine pineal arylalkylamine N-acetyltransferase, N-acetylserotonin and melatonin increase 5- to 10-fold. No significant changes in hydroxyindole-O-methyltransferase, 5-hydroxytryptamine, 5-hydroxyindoleacetic acid, 5-hydroxytryptophol, 5-methoxyindoleacetic acid and 5-methoxytryptophol are detected at this time. Administration of cycloheximide inhibits the rise in N-acetyltransferase and N-acetylserotonin, but not melatonin. Unexpectedly, 5-methoxytryptophol increases after cycloheximide treatment. Taken together, these results although consistent in part with a role for serotonin N-acetylation in the regulation of melatonin synthesis in sheep, indicate that an N-acetyltransferase-independent mechanism may also be involved.