The Influence of Some Pteridines on the Circadian and Seasonal Rhythmicity of Hydroxyindole-O-Methyltransferase (HIOMT) in the Pineal Gland of 42-days-old Male Wistar Rats

ABSTRACT The pineal of 42 days old male Wistar rats was studied with regard to the influence of some pteridines on HIOMT activity in different seasons of the year. The circadian rhythmicity was influenced by pteridines, when the maximal HIOMT activity was measured at 24.00 o'clock (in June and in the period from half September till the beginning of October). There was no or only a small influence detectable, when the maximal HIOMT activity was determined at 04.00 o'clock (in April and in the last half of October). These alterations are probably of physiological importance.