Diurnal variation in the serotonin content and turnover in the pineal gland of the Syrian hamster.

Serotonin and 5-hydroxyindoleacetic acid were measured in the pineal gland of Syrian hamsters by high performance liquid chromatography over a period of 24 h. A distinct 24 h rhythm was detected for both indoles. Turnover studies revealed a higher rate of serotonin synthesis during the day than during the night. We therefore suggest that the serotonin content in the pineal gland of the Syrian hamster is regulated by changes in its synthesis rate, rather than by changes of serotonin catabolism, via N-acetyltransferase activity.