Effects of coronary arterial reperfusion on beta-adrenergic receptor-adenylyl cyclase coupling

The effects of 1 h of coronary arterial occlusion (CAO) followed by 15 min reperfusion (CAR) were examined in nine conscious dogs. Ischemia was verified by decreased regional blood flow (radioactive microspheres) and loss of systolic regional wall motion in the ischemic zone. beta-Adrenergic receptor density assessed by 125I-labeled cyanopindolol binding in a crude membrane fraction tended to decrease but was not significantly different. However, adenylyl cyclase activity and the guanine nucleotide stimulatory protein (Gs) were reduced in ischemic subendocardium compared with nonischemic subendocardium. The fraction of beta-adrenergic receptors binding agonist with high affinity increased in ischemic subendocardial and subepicardial layers. Compared with prior data in experiments with 1 h CAO without CAR, the increase in beta-adrenergic receptor density that occurs with myocardial ischemia is rapidly reversed with CAR of 15 min duration, while the decreased fraction of receptors binding agonist with high affinity was reversed to an increase in high-affinity receptors. The global decreases in adenylyl cyclase and Gs, which have been observed with simple CAO, persist but are observed selectively in the previously ischemic subendocardium after CAR. Thus both CAO and CAR affect beta-adrenergic receptors and adenylyl cyclase differently. During CAR, increased numbers of beta-adrenergic receptors binding agonist with high affinity occur potentially as a compensatory mechanism in the face of persistent reductions in adenylyl cyclase activity and Gs.