title: Inhibition of day time, but not isoproterenol-stimulated pineal N-acetyltransferase activity by an unidentified pineal compound.
abstract: Day time rat pineal N-acetyltransferase (P-NAT) activity is higher when homogenate used for incubation is diluted. Samples containing homogenate equivalent to 1/80 pineal gland had highest enzyme activity when compared with samples that contained homogenate equivalent to 1/40 and 1/20 pineal gland, respectively. Thus P-NAT activity is inhibited by a compound present in the pineal gland of the rat. This inhibition was not found in pineal glands of animals that had been injected with isoproterenol. Furthermore day time P-NAT activity is inhibited by excess of substrate, whereas even at 10 mmol/l of substrate isoproterenol stimulated P-NAT activity is not. It is suggested that these two phenomena are involved in the physiologic regulation of the circadian changes of P-NAT activity.
mesh_terms: D000123:Acetyltransferases / Q000037:antagonists & inhibitors*; D000818:Animals; D001191:Arylamine N-Acetyltransferase / Q000037:antagonists & inhibitors*; D002940:Circadian Rhythm; D007545:Isoproterenol / Q000494:pharmacology*; D007700:Kinetics; D008297:Male; D010870:Pineal Gland / Q000032:analysis* / Q000201:enzymology; D051381:Rats; D011919:Rats, Inbred Strains; D012701:Serotonin / Q000378:metabolism
chemical_list: D012701:Serotonin; D000123:Acetyltransferases; D001191:Arylamine N-Acetyltransferase; D007545:Isoproterenol