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This study was designed to evaluate the effects of alterations of beta-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 beta1-blockade with practolol; 3) combined beta1 and beta2 blockade with propranolol; and 4) selective beta2 stimulation. Neither practolol nor propranolol significantly altered the volume or distribution of blood flow into the normally perfused or ischaemicmyocardial areas, while beta2 stimulation increased blood flow to the normally perfused myocardium from 1.13 +/- 0.12 to 1.28 +/- 1.10 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 myocardiu, beta2 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 beta2-agonist administration. Thus, although beta2 stimulation produced a modest increase in blood flow to normally perfused myocardium, in the setting of acute myocardial ischaemia, beta2 stimulation resulted in a significant decrease in intercoronary collateral flow.
Melby et al. (Tue,) studied this question.