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 beneficial during myocardial ischemia, but could be opposed by their peripheral vasoconstrictive effect. We studied the effects of mivazerol during periods of moderate coronary artery stenosis in anesthetized dogs. Mivazerol decreased heart rate (from 125 +/- 6 to 106 +/- 6 bpm) and cardiac output (from 4.4 +/- 0.6 to 1.8 +/- 0.2L/min) under normal conditions, while mean arterial pressure did not change. Mivazerol reduced blood flow in nonischemic myocardium and in the ischemic epicardial layer, but blood flow was preserved in the ischemic midmyocardial and subendocardial layer. Mivazerol had no effect on myocardial oxygen extraction during the stenoses, and regional myocardial oxygen consumption was unchanged. However, mivazerol decreased myocardial oxygen demand from 4.51 +/- 0.51 to 3.17 +/- 0.24 mumol.min-1.g-1, thereby reducing oxygen deficiency of ischemic myocardium to values significantly lower than in the placebo group (from 1.07 +/- 0.32 to 0.47 +/- 0.41 mumol.min-1.g-1). Mivazerol had no effect on myocardial lactate production during the stenoses. We conclude that mivazerol reduced myocardial oxygen demand while blood flow was preserved in the inner layers of ischemic myocardium.