THE EFFECTS OF ALPHA(2)-ADRENERGIC STIMULATION WITH MIVAZEROL ON MYOCARDIAL BLOOD-FLOW AND FUNCTION DURING CORONARY-ARTERY STENOSIS IN ANESTHETIZED DOGS

The central sympatholytic effect of alpha(2) agonists may be beneficia l during myocardial ischemia, but could be opposed by their peripheral vasoconstrictive effect. We studied the effects of mivazerol during p eriods of moderate coronary artery stenosis in anesthetized dogs. Miva zerol decreased heart rate (from 125 +/- 6 to 106 +/- 6 bpm) and cardi ac output (from 4.4 +/- 0.6 to 1.8 +/- 0.2 L/min) under normal conditi ons, while mean arterial pressure did not change. Mivazerol reduced bl ood flow in nonischemic myocardium and in the ischemic epicardial laye r, but blood flow was preserved in the ischemic midmyocardial and sube ndocardial layer. Mivazerol had no effect on myocardial oxygen extract ion during the stenoses, and regional myocardial oxygen consumption wa s unchanged. However, mivazerol decreased myocardial oxygen demand fro m 4.51 +/- 0.51 to 3.17 +/- 0.24 mu mol . min(-1) . g(-1), thereby red ucing oxygen deficiency of ischemic myocardium to values significantly lower than in the placebo group (from 1.07 +/- 0.32 to 0.47 +/- 0.41 mu mol . min(-1) . g(-1)). Mivazerol had no effect on myocardial lacta te production during the stenoses. We conclude that mivazerol reduced myocardial oxygen demand while blood flow was preserved in the inner l ayers of ischemic myocardium.