Daily time course of the contents in monoamines and their metabolites in the pineal gland of Syrian hamster

Abstract

Twenty-four h changes in endogenous tyrosine hydroxylase (TH) activity, monoamines and their metabolites as well as N-acetyltransferase (NAT) activity and melatonin content were investigated in the Syrian hamster pineal gland. Both NAT activity and melatonin content exhibited an expected rise 8 h (0400 h) after darkness onset. Pineal dopamine (DA) and 3,4-dihydroxyphenyl acetic acid (DOPAC) levels were highest during the dark phase reaching a peak at 0200 h, just prior to the rise in melatonin production. However no significant difference were found in both norepinephrine (NE) and TH activity levels during the 24 h period. However, in the present study, the rat pineal gland exhibited a clear day/night difference in its TH activity. These data suggest a possible role of pineal DA in the induction of melatonin synthesis in addition to its function as a NE precursor in the Syrian hamster pineal gland and also indicate that catecholamines may act on the hamster pineal in a different manner than in the rat.