Daily and seasonal rhythmicity in the methylation of pineal indolic compounds in adult male golden hamsters, kept under natural conditions.

Seasonal rhythmicity in the reproductive cycle was demonstrated in golden hamsters exposed to natural conditions. Testes regress in weight and function from October up to April. Reproductive functional testes are found in June. Although less marked, body weight also shows seasonal variations: a retarded growth in winter and early spring. In the pineal gland of these animals diurnal and seasonal rhythmicity was found in the synthesis of various MI. It has been concluded that rhythms in the pineal of animals kept under artificial conditions are often more pronounced as compared to those in hamsters kept under natural conditions. Melatonin (aMT) synthesis was observed during the day as well as during the night. A certain resemblance in patterns of day/night rhythms as to aMT and 5-methoxytryptamine (MT) production was reported suggesting a physiological role of MT. To facilitate the discussion on seasonal rhythmicity the average synthesis per day of the 5-methoxyindoles (MI) was calculated. During the period of gonadal regression in fall and early winter, MT and aMT, which are both generally accepted as pineal antigonadotropins, showed opposite patterns in rhythms of mean synthesis; MT decreased but aMT increased from October up to December. It was suggested that under natural conditions MT may induce and aMT maintain gonadal atrophy. Furthermore, also other MI showed relatively high amounts of production, at least in November. The period of recrudescence was characterized by a high synthesis of 5-methoxytryptophan (MW), 5-methoxytryptophol (ML) and O-acetyl-5-methoxytryptophol (aML). This confirms an earlier suggestion that aML can be considered a counter-antigonadotropic substance of the hamster pineal gland. Therefore it was concluded that, apart from MT and aMT, also other MI may be of physiological importance in the regulation of gonadal atrophy.