Abstract
3', 5'-cyclic adenosine monophosphate (cyclic AMP) systems in the anesthetized rat adrenal medulla were studied using the technique of a direct infusion of various agents into the adrenal gland, and such is referred to as ‘the retrograde-adrenal vein infusion’ and ‘the intra-adrenal infusion’. A direct administration of acetylcholine into the adrenal gland by the retrograde infusion produced a rapid stimulation of the catecholarnine-release, followed by a delayed activation of the adenylate cyclase in the adrenal medulla. The acetylcholine-induced increase in hormonal secretion and cyclic AMP levels was completely blocked by hexamethonium, indicating the mechanism of nicotinic trans-synaptic stimulation. Intra-adrenal infusion of epinephrine also prevented an increase in cyclic AMP accumulation induced by acetylcholine. This suggests an inhibitory mechanism on the cyclic AMP systems by catecholarnines within the medullary cells. The infusion of propranolol or phentolamine into the gland, in some cases denervated, increased cyclic AMP amounts in the medulla, suggesting a decrease in catecholamine-induced inhibition by a or β-antagonists. These results favor the assumption that the mechanism of catecholamine inhibition of the adenylate cyclase system is mediated by adrenergic interaction. The present studies suggest a mechanism of regulation by catecholamines of the cyclic AMP systems at the early stage of traps-synaptic stimulation, such leading to the delayed increase in the adenylate cyclase activation of the adrenal medulla in vivo.
