Regional myocardial tissue blood flow during β-adrenergic blockade in cat hearts with acute ischaemia

Summary. Selective β₁ or β₂-adrenergic blockade was achieved by practolol or IPS 339, respectively, in cats with acute ligation of a coronary artery. During blockade, heart rate was kept constant by atrial pacing and blood pressure reduction was prevented by aortic clamping. Regional myocardial blood flow was measured by the distribution of 15 μm labelled microspheres. Practolol slightly reduced epicardial blood flow in ischaemic myocardium, while blood flow in border and normally perfused myocardium remained unchanged. Following IPS 339, myocardial tissue flow increased in normally perfused myocardium, on average by 37% in the endocardium and 30% in the epicardium. No changes occurred in the other regions. The flow changes brought about by IPS 339 were unrelated to haemodynamic changes, and the coronary vascular resistance was reduced. These results are indicative of coronary vasodilation related to β₂-adrenergic receptor blockade and was confined to well-oxygenated areas surrounding the acutely ischaemic zone.