Selective necrosis of cardiac and skeletal muscle induced experimentally by means of proteolytic enzyme solutions given intravenously.

Focal necrosis of cardiac and skeletal muscle was produced regularly in rabbits by means of a single intravenous or intra-arterial injection of a solution of crude papain. Similar lesions were produced in rats and mice injected with this material. The intravenous injection of solutions of ficin, trypsin, and streptokinase also resulted in comparable lesions of cardiac and skeletal muscle in rabbits. The lesions in the myocardium became apparent within 6 hours after injection of the enzyme; they consisted essentially of focal degeneration and necrosis of the sarcoplasm and myofibrils within a segment of muscle fiber. An inflammatory reaction consisting of a small number of polymorphonuclear leukocytes and considerable numbers of mononuclear cells, and often multi-nucleated giant cells, was present within the lesions. In some instances severely damaged fibers were replaced by fibrous tissue and in others proliferation of muscle cell nuclei and restitution of the fiber appeared to take place. Similar changes of a lesser degree were also observed in skeletal muscle. The findings are discussed in connection with the pathogenesis of the anatomical lesions of rheumatic fever, periarteritis nodosa, and other hypersensitivity states.