Catecholaminergic activity and 3',5'-cyclic adenosine monophosphate levels in heart right ventricle after naloxone induced withdrawal.

This study evaluated the adaptive changes in noradrenergic neurons and the concomitant production of cAMP during morphine dependence and withdrawal in the right ventricle of the rat. Rats were made dependent on morphine by morphine pellet implantation for 7 days. On the day of sacrifice animals received an acute injection of saline or naloxone (1 mg/kg s.c.) and were decapitated 30 min later. Pretreatment with propranolol 15 min prior to naloxone was conducted to evaluate the possible implication of beta-adrenoceptors. The contents of noradrenaline and dopamine and their metabolites were examined. After naloxone administration to morphine-dependent rats (withdrawal) there was a pronounced increase in the content of normetanephrine and 3,4-dihydroxyphenylacetic acid and increased noradrenaline and dopamine turnover. In addition cAMP levels were increased after naloxone administration to morphine-treated rats. Propranolol did not block the hyperactivity of catecholaminergic neurons or the enhancement of cAMP observed in the heart during withdrawal. The present results indicate that heart catecholaminergic neurons play a significant role in the alterations in heart functions during morphine abstinence syndrome and suggest that those alterations are mediated through cAMP.