THE A(2A) ADENOSINE RECEPTOR MEDIATES CORONARY VASODILATION

The coronary vasodilation caused by adenosine is due to activation of A(2) adenosine receptors (A(2)AdoRs), but the subtype or subtypes of A (2)AdoR (A(2A) and/or A(2B)) that mediate this action are uncertain. T he purpose of this study was to test the hypothesis that A(2A)AdoRs me diate coronary vasodilation caused by exogenous or endogenous adenosin e in the guinea pig isolated perfused heart. The newly described A(2A) AdoR antagonist SCH58261 was used to selectively block A(2A)AdoRs. Att enuations by SCH58261 of increases in coronary conductance (A(2) respo nse) and of atrioventricular nodal conduction time (A(1) response) cau sed by exogenous and endogenous adenosine and by agonists with relativ e selectivity for A(2A) and A(1)AdoRs were measured. The CGS21680-indu ced increase of coronary conductance was antagonized by SCH58261 in a concentration-dependent and competitive manner with a K-B value of 5.0 1.