Oxygen consumption and coronary vascular tone in the isolated fibrillating dog heart

An improved method of determining the coronary flow and myocardial oxygen consumption of the Langendorf dog heart preparation with ventricular fibrillation is described. Stable levels of these two functions are obtained for a 6-hour period. The effects of acetylcholine, epinephrine, levarterenol, isoproterenol, methoxamine and Pitressin are studied. Further, the effects of the sympathomimetic amines are studied before and afteŕ treatment with Dibenzyline and the dichloroanalogue of isoproterenol. A significant correlation between coronary flow and myocardial oxygen consumption is found in all cases. It is concluded that epinephrine and levarterenol cause coronary vasodilation by increasing the myocardial oxygen consumption though initially producing a vasoconstriction. Isoproterenol affects myocardial oxygen consumption and has no direct vascular effect. These studies are interpreted as revealing the existence of sympathetic vasoconstrictor and parasympathetic vasodilator receptors and the absence of pure sympathetic vasodilator receptors in the coronary vessel wall.