Loss Of Myocardial Contractility Induced In Isolated Mammalian Hearts By Streptolysin-O

Infections with group A streptococci are considered to be responsible for the development of important structural and functional changes in the hearts of human beings and experimental animals (1, 2), but the manner in which streptococcal infections bring about these changes remains obscure. Of the diverse extracellular products elaborated during the growth of group A strep- tococci, only two---streptococcal proteinase and streptolysin O--are known to have an effect upon the heart. A single intravenous injection of crystalline streptococcal proteinase has been shown to cause focal necrosis of the myo- cardium in rabbits, mice, and guinea pigs (3); and solutions containing strep- tolysin O have been found to induce systolic contracture of the isolated frog heart (4-6). The studies now to be presented demonstrate that a minute quan- tity of streptolysin O brings about a prompt and irreversible loss of myocardial contractile power when per(used through the isolated hearts of guinea pigs, rabbits, and rats.