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.