Regional myocardial tissue blood flow during sequential beta 1- and beta 2-adrenergic blockade in cat hearts with...

beta-Adrenergic blockade was imposed on cats with ischaemic regions of the left ventricle produced by coronary artery occlusion. Ten animals first received a beta 1-blocking agent (atenolol) followed by a beta 2-blocking agent (IPS 339). In ten more animals this sequence was reversed. Combined blockade, obtained after both agents were administered, showed clear reduction of tissue blood flow in all areas of the ventricle, except for the central ischaemic zone. The flow reduction could be ascribed to bradycardia and reduced coronary perfusion pressure. By analysing the sequential changes it was evident that blockade of beta 1-adrenergic receptors was responsible for the haemodynamic changes, and the coronary vascular resistance rose so as to match the quantity of blood flow to the functional state of the ventricle. Blockade of beta 2-receptors by IPS 339, however, showed no evidence of coronary vasoconstriction but rather maintained vascular resistance at an unchanged level despite a weak beta 1-adrenergic blocking effect.