Effect of cyclophosphamide on the acute phase of experimental myocardial infarction in rats.

The effect of a single dose of the cytotoxic drug cyclophosphamide on the severity of acute myocardial infarction in conscious rats has been studied. One and 4 days after the i.p. injection of 100 mg kg-1 of the drug, the survival rate of rats subjected to coronary ligation was significantly increased. The occurrence of fatal arrhythmias was markedly reduced. The peripheral white blood cell count was profoundly lowered. On the first day after pretreatment, moderate granulocytosis with severe lymphopenia occurred. Four days following the administration of cyclophosphamide, marked granulocytopenia also ensued. In this stage, restoration of white blood cell count by cell suspension prepared from the spleen of normal rats did not significantly affect the cardioprotective effect of cyclophosphamide. The data provide additional evidence that protein synthesis is involved in the early phase of myocardial infarction. The significance of leukocytes in the phenomenon is briefly discussed.