Prevention of myocardial lesions in JCR:LA-corpulent rats by nifedipine.

Male rats of the JCR:LA-corpulent strain spontaneously develop atherosclerosis and myocardial lesions if corpulent. The corpulent rats exhibit a marked very low density hyperlipidemia and insulin resistance. The incidence of both vascular and myocardial lesions correlates strongly with the hyperinsulinemia, but not with the hyperlipidemia. Corpulent male rats were chronically treated with nifedipine or acetylsalicylic acid to explore the roles of smooth muscle spasm and platelet activity in induction of the myocardial lesions. Acetylsalicylic acid treatment was associated with no significant changes in fasting glucose, insulin, or lipid concentrations. Nifedipine caused no significant changes in glucose concentration but was associated with mildly increased insulin levels. Treatment with nifedipine resulted in significant decreases in serum triglyceride concentrations. The decreases were confined to longer-chain triacylglycerol molecular species with no change in the concentration of molecular species with 48 or 50 acyl carbon atoms. There was no effect on myocardial lesion frequency with acetylsalicylic acid treatment. In contrast, nifedipine prevented the development of old organized scarred lesions. This effect is similar to that seen with treatments that markedly reduce the insulin resistance. These findings suggest that platelet-initiated thrombus formation is not an important factor in lesion formation in the JCR:LA-cp rat, but that smooth muscle spasm is probably important.