Na⁺, K⁺, Ca⁺⁺, and Mg⁺⁺ action on coronary vascular resistance in the dog heart

¹ Division of Environmental Medicine, U.S. Army Medical Research Laboratory, Fort Knox, Kentucky

Local effects of major cations on coronary vascular resistance were studied in the beating dog heart. This was accomplished by shunting the blood around the heart and lungs, clamping the arch of the aorta and perfusing arterial blood at a constant rate into the ascending aorta. Perfusion pressure was measured during intracoronary infusion of isotonic solutions of NaCl, KCl, CaCl₂, MgCl₂, and MgSO₄ and hypertonic solutions of NaCl and KCl at rates which raised cation concentrations in coronary blood without significantly affecting concentrations generally within the body. Coronary vascular resistance decreased as a function of the infusion rate of isotonic solutions of KCl, MgCl₂, and MgSO₄ and increased as a function of the infusion rate of an isotonic solution of CaCl₂. Isotonic NaCl had no effect. Resistance changes occurred before measurable change in the proportion of a minute spent in electrical systole by the ventricle. These findings, together with those previously reported for the dog foreleg, suggest that the coronary vascular bed is actively dilated by localized slight increase in plasma concentration of K or Mg and actively constricted by localized slight increase in plasma concentration of Ca.