Myocardial ischemic injury induced by isoproterenol in the rabbit: biochemical and chemical alterations.

The development of a model of chronic myocardial ischemic injury (MII) in rabbits by administering increasing doses of isoproterenol (ISO) is described. Repeated s.c. injections of increasing doses of ISO (0.5 mg/kg, on day 1 to 15.5 mg/kg, on day 15) resulted in an increase in serum glucose, free fatty acids and creatine phosphokinase. Examination of hearts from ISO-treated rabbits revealed marked hypertrophy of the left ventricle and an increase in total water content. Biochemical analysis showed an increase in left ventricular hydroxyproline and a decrease in ATP and glycogen content following ISO-treatment. Ion measurements revealed extensive accumulation of Na and Ca, with the Ca being preferentially accumulated in the mitochondria. Measurement of subcellular organelle marker enzymes showed decreases in the sarcolemmal Na+-K+-stimulated (ouabain-sensitive), mitochondrial (azide-sensitive) and sarcoplasmic reticulum ATPase activities in the ISO-treated animals. Analysis of lysosomal enzyme activities in myocardial homogenates showed significant decreases in the latency of N-acetyl-beta-glucosaminidase and cathepsin D. The above biochemical alterations in ISO-induced MII generally parallel changes previously seen in the rabbit following acute coronary artery ligation. The present model allows the study of MII uncomplicated by some uncertainties arising from the surgical or anesthetic procedures employed in acute "open-chest" preparations and would permit long-term follow-up studies of pharmacological interventions. The susceptibility of the rabbit to experimental atherosclerosis should allow the development of an experimental model of MII which more closely approximates the clinical situation.