Indoleamine metabolism in the pineal gland of the Chinese hamster, Cricetulus griseus.

Day- and nighttime contents of pineal melatonin and other indoleamines were measured in the Chinese hamster, Cricetulus griseus. The hamsters were inbred in our colony and kept in LD 14:10. Absolute levels of pineal melatonin and N-acetylserotonin contents were extremely low, but showed a significant circadian rhythm with a minor peak during the light period. Pineal hydroxytryptophan and serotonin (5HT) contents were also found to be higher in the light period. The activity of N-acetyltransferase in the pineal was higher in the light period than in the dark period, whereas there was no difference in hydroxyindole-O-methyltransferase activity between the light and dark periods. The uptake level of tryptophan into the pineal gland was higher in the light period than in the dark period. These results suggest that the 5HT synthesis pathway and/or tryptophan uptake may be involved in forming the circadian rhythm of 5HT content in the Chinese hamster pineal gland.