Metoprolol reduces ‘compensatory’ coronary blood flow following occlusion of an adjacent branch without altering post-occlusion hyperaemia

In pentobarbitone anaesthetised, thoracotomised dogs, blood flow in one (circumflex; LCX) branch of the left coronary artery increases when an adjacent (anterior descending; LAD) branch is occluded. We show that this ‘compensatory blood flow’ increase results from an enhanced regional myocardial contractility, as assessed using piezoelectric crystals, and that this is to compensate for a marked decrease in segmental shortening (SS) in the region supplied by the occluded vessel. These changes in regional contractility are relatively unaffected by the intravenous administration of metoprolol whereas the LCX flow change is markedly reduced, suggesting a major contribution of coronary vascular β1-adrenoceptors to such ‘compensatory’ flow changes.