Increased α-adrenergic receptors in ischemic cat myocardium. A potential mediator of electrophysiological derangements

Abstract

We have recently demonstrated enhanced α-adrenergic responsiveness assessed electrophysiologically in ischemic and reperfused myocardium. This study was performed to determine whether ischemia alters α1-adrenergic receptor number (B(max)) or affinity (K(D)) based on [3H]prazosin binding. Within 30 min after occlusion, B(max) increased in ischemic regions to 207% of control to 27±4 fmol/mg protein, with the increase persisting (+141% of control) during early reperfusion (2 min), before returning to control base-line values (13±1.6) after 15 min of reperfusion. K(D) was not altered at any interval studied. Beta receptor number ([3H]dihydroalprenolol) and Na+-K+ ATPase activity were comparable in control compared to ischemic myocardium although β-receptor B(max) and K(D) in both regions decreased during early reperfusion. Thus, the enhanced α-adrenergic responsivity previously recognized with ischemia and reperfusion is correlated with an increase in α1-adrenergic receptors.