Loss of myocardial contractility induced in isolated mammalian hearts by streptolysin O.

When solutions containing minute quantities of streptolysin O, previously activated with cysteine, were added to a salt and glucose medium that was being perfused by way of the coronary arteries through the vigorously beating isolated hearts of guinea pigs, rabbits, and rats, the amplitude of myocardial contraction decreased abruptly, often to zero. The effect was usually accompanied by a diminution in the flow of perfusion fluid, probably owing to spasm of the coronary arteries. The diminution in coronary flow was transitory, however, lasting as a rule only 2 or 3 minutes, while the loss of myocardial contractile power was permanent and irreversible. No decrease in myocardial contractility was obtained when the streptolysin O was not previously activated with cysteine, or when the streptolysin O was inhibited by cholesterol or by specific antibody, the findings pointing to streptolysin O as the active cardiotoxic agent.