Myocardial adenosine stimulates release of cyclic adenosine monophosphate from capillary endothelial cells in guinea pig heart.

Activation of coronary endothelial cell adenylate cyclase was studied in the isolated guinea pig heart by prelabelling endothelial adenine nucleotides using intracoronary infusion of [3H]-adenosine, and measuring the coronary efflux of [3H]-cyclic adenosine monophosphate (cAMP). Hypoxia (30% O2) caused a 4-fold increase in coronary release of [3H]-cAMP, which was decreased by 63% by infusion of the adenosine receptor antagonist, theophylline (50 microM). During normoxic control conditions, degrading adenosine to non-vasoactive inosine by intracoronary infusion of adenosine deaminase (1.7 U/ml) caused a 20% decrease in the release of [3H]-cAMP. The effect of adenosine deaminase was reversed by a specific enzyme inhibitor erythro-9-(2-hydroxy-3-nonyl)adenine hydrochloride. Coronary efflux of [3H]-cAMP during intracoronary infusion of 1 microM adenosine triphosphate (ATP), adenosine diphosphate or adenosine monophosphate (AMP) (plus adenosine deaminase 8 U/ml) was only 13% of that due to 1 microM adenosine. Adenosine receptor blockers theophylline and CGS 15943A caused equivalent inhibition of the coronary vasodilator actions of adenosine and ATP. Intracoronary infusion of prostaglandin E1 and the beta 2-adrenergic agonist procaterol caused parallel, dose-dependent increases in coronary conductance and the venous release of [3H]-cAMP. It is concluded that (1) under both normoxic and hypoxic conditions, adenosine formed by the heart may activate endothelial cell adenylate cyclase via membrane adenosine receptors, (2) coronary receptors for adenosine and ATP share common ligand affinities but ATP receptors are not coupled to adenylate cyclase, and (3) other vasodilators known to activate endothelial adenylate cyclase in vitro cause parallel increases in coronary conductance and adenylate cyclase activity in the beating heart.