Adenosine 5'-monophosphate enhances the dark and isoproterenol-induced rise in rat pineal N-acetyltransferase activity.
Exposure of rats to light during darkness or blockade of the pineal beta-adrenoceptor in stimulated pineal glands results in a rapid fall in pineal N-acetyltransferase (NAT) activity. Maintenance of a high level of NAT activity requires continuous stimulation of the pineal beta-adrenoceptors. It is not known what factors in the pinealocyte are responsible for this rapid inactivation of NAT activity. In the present study we have attempted to investigate a possible regulatory role of 5'-AMP on pineal NAT activity. The results show that 5'-AMP further enhances dark-induced as well as isoproterenol-induced NAT activity by approximately 3-fold but does not alter unstimulated daytime NAT activity. Theophylline, an inhibitor of 5'-AMP synthesis, when administered early in the dark phase, caused a rise in pineal cAMP with a concomitant fall in pineal NAT activity. These findings indicate that 5'-AMP could play a role in the activation of pineal NAT. The possibility that the rapid inactivation of NAT is due to a rapid removal of 5'-AMP by, for example, phosphorylation, remains to be investigated.
Olivieri
G
G
Department of Biochemistry and Microbiology, Rhodes University, Grahamstown, South Africa.
Daya
S
S
D000249:Adenosine Monophosphate / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D000818:Animals; D001191:Arylamine N-Acetyltransferase / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism; D003623:Dark Adaptation; D007545:Isoproterenol / Q000494:pharmacology*; D008027:Light; D010870:Pineal Gland / Q000187:drug effects / Q000201:enzymology*; D051381:Rats; D011919:Rats, Inbred Strains; D013806:Theophylline / Q000494:pharmacology
D000249:Adenosine Monophosphate; D013806:Theophylline; D000242:Cyclic AMP; D001191:Arylamine N-Acetyltransferase; D007545:Isoproterenol