Effect of selective beta-adrenergic blockade and stimulation on regional myocardial blood flow following acute coronary artery occlusion in the awake dog

Summary: This study was designed to evaluate the effects of alterations of β-receptor activity on intercoronary collateral blood flow after acute coronary artery occlusion in the awake dog. Blood flow following acute circumflex coronary occlusion was measured during: 1) control conditions; 2) selective β₁-blockade with practolol; 3) combined β₁ and β₂ blockade with propranolol; and 4) selective β₂ stimulation. Neither practolol nor propranolol significantly altered the volume or distribution of blood flow into the normally perfused or ischaemic myocardial areas, while β₂ stimulation increased blood flow to the normally perfused myocardium from 1.13 ± 0.12 to 1.28 ± 0.10 cm³·min^-1·g^-1 (P <0.05). This increase in flow, which was directed preferentially to the subepicardium, was mediated by a significant decrease in coronary vascular resistance. In contrast to the effect on normally perfused myocardium, β₂ stimulation resulted in a 47 ± 12% decrease in collateral flow into the central ischaemic zone (P <0.05), which was mediated by a combination of decreased arterial pressure and increased collateral vascular resistance during β₂-agonist administration. Thus, although β₂ stimulation produced a modest increase in blood flow to normally perfused myocardium, in the setting of acute myocardial ischaemia, β₂ stimulation resulted in a significant decrease in intercoronary collateral flow.