The healing of frog heart lesions induced by isoproterenol injections.

Isoproterenol (IPR) induces myocardial lesions in R. pipiens adapted to +25 degrees C, but not to +8 degrees C. The spontaneous healing of these lesions in the form of ventricular wall aneurysms occurs during the first three weeks after IPR, and the ultrastructure of the myocardial cells in fully restored from the fourth week after IPR. Leukocytes, adhering to the lacunar endothelium and including phagocytic vacuoles, appear 8-15 days after IPR. Severely altered heart muscle cells then contain myelin figures or a pyknotic nucleus. In the acute stage of the IPR-lesions, heart muscle preparations from the ventricular wall show a very lowered resistance towards cyanide anoxia as judged from the isometric force decay. During the seven weeks of observation after IPR the resistance to cyanide anoxia is continuously improved almost to normal values. Thus restoration of structure and function occurs in parallel.