Some Properties of a Cardioactive Substance Isolated From Human Plasma

Abstract

Some effects of a relatively low molecular weight substance, isolated from human plasma, on isolated amphibian and mammalian cardiac muscle and on intact rabbits have been studied. This cardioactive plasma substance elicited a positive inotropic response from isolated isometrically contracting papillary muscle of rabbits, dogs, and monkeys, from trabeculae carneae of rats, and from ventricular muscle of toads. Its positive inotropic activity was associated with a shortened duration of action potentials. Studies on intact animals showed that the intravenous injection of this substance raised systemic pressures, raised right and left ventricular systolic pressures, and increased cardiac output. Adrenergic blocking drugs failed to block the inotropic and pressor effects of freshly isolated cardioactive plasma substance.