Hepatic cylic AMP generation and ornithine decarboxylase induction by glucagon and beta adrenergic agonists

Abstract

The relationship of hepatic ornithine decarboxylase (ODC) activity to cyclic AMP levels and nutritional status was studied in the preweanling rat. Previous studies demonstrated that 2 hr without food causes a loss of hepatic ODC induction after glucagon or catecholamine injection. Isoproterenol or glucagon administration produced increased hepatic cyclic AMP and tyrosine aminotransferase activity which were not prevented by nutritional deprivation. Blockade of hepatic β 2 receptors by the selective antagonist ICI 118, 551 prevented increased cAMP levels and ODC activity after isoproterenol administration. Blockade of β 1 receptors by atenolol did not prevent increased cAMP levels or ODC induction by isoproterenol although it did block activation of cardiac ODC. The phosphodiesterase inhibitor R020-1724 increased hepatic cAMP levels as well as ODC and TAT activities, although the increase in ODC activity was attenuated by nutritional deprivation. R020-1724 also potentiated the induction of hepatic ODC after glucagon or isoproterenol administration. Administration of 8-bromo cAMP elevated hepatic ODC activity regardless of nutritional status but also elevated serum levels of growth hormone and corticosterone. Hepatic ODC induction by glucagon or β 2 agonists can be dissociated from changes in cAMP levels during nutritional deprivation.