Isoproterenol induced myocardial lesions in the immunized and non-immunized rat. II. Histopathological lesions after specific immunization.

Rats killed 24 hours after a single injection of 30–100 mg/kg Isoproterenol (-iso-propyl noradrenaline), show focal myocardial necrosis. Animals previously immunized against homologous (rat) heart homogenate showed a marked increase in severity and extent of the lesions. Immunization against rabbit heart caused a lesser degree of enhancement; rat kidney, rabbit serum and kidney and saline—adjuvant emulsion as antigens, gave results similar to the controls. There was no correlation between the level of circulating anti-heart antibodies, as measured by passive haemagglutination, and the severity of the myocardial necrosis. Within each treatment group, however, animals with higher titres tended to show greater myocardial damage. It is suggested that circulating anti-heart antibodies, normally non-toxic , become cytopathogenic after the myofibre cell barrier is broken down by Isoproterenol.