DAILY TIME-COURSE OF THE CONTENTS IN MONOAMINES AND THEIR METABOLITESIN THE PINEAL-GLAND OF SYRIAN-HAMSTER

Twenty-four h changes in endogenous tyrosine hydroxylase (TH) activity , monoamines and their metabolites as well as N-acetyl-transferase (NA T) activity and melatonin content were investigated in the Syrian hams ter 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 durin g 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 clea r day/night difference in its TH activity. These data suggest a possib le role of pineal DA in the induction of melatonin synthesis in additi on to its function as a NE precursor in the Syrian hamster pineal glan d and also indicate that catecholamines may act on the hamster pineal in a different manner than in the rat. (C) 1997 Elsevier Science Irela nd Ltd.