Effect of time on the response to cyanide anoxia of frog heart damaged by isoproterenol.

Isoproterenol (IPR) induces damage to the heart of frogs living at 25 degrees. The resistance of an isometric ventricular strip to histotoxic anoxia induced by cyanide is significantly reduced 4 hours after one injection of IPR and still more after repeated injections. Macroscopically visible heart lesions are observed only on the first two days after the second injection of IPR. The response of the heart muscle preparation to cyanide is then continuously improved during 3-4 weeks after IPR and the disturbance of the myocardial function is thus only temporary and may at least partly be induced by metabolites of the catecholamine.