Effects of vanadate on heart and circulation

In anesthetized cats vanadate (Na3VO4) up to 0.5 mg/kg increased blood pressure and left ventricular end-diastolic pressure (LVEDP) but decreased the force of contraction and heart rate. At 1 mg/kg, LVEDP increased markedly in parallel with an elevation of the ST segment of the electrocardiogram and a pronounced decrease in blood pressure; these effects were reversible within a few minutes. In isolated Langendorff heart preparations of guinea pigs perfused at constant pressure, vanadate decreased flow rate (EC50 = 5.3 mumoles/liter) and contractile force (EC50 = 6.9 mumoles/liter). Vanadate increased tension in isolated aortic strips of cats (EC50 = 115 mumoles/liter) and rabbits (EC50 = 435 mumoles/liter). Vanadate also increased the force of isometric contractions of papillary muscles of guinea pigs, cats, and rabbits, the EC50 values being 124, 110, or 66 mumoles/liter, respectively. We conclude that the negative ionotropic action of vanadate is brought about by marked coronary constriction occurring at concentrations which are too low to have a direct positive action on ventricular myocardium.