Atherogenesis in two strains of obese rats The fatty Zucker and LA/N-corpulent

Two strains of obese rats, the fatty Zucker and the LA/N-corpulent have been compared at 6 months age for the presence of vascular and myocardial disease. Both strains, when obese, exhibit a VLDL hyperlipidemia with elevated triglycerides and moderate elevations of plasma cholesterol concentrations compared to the lean rats of the same strain. The hyperlipidemia is more modest in the fatty Zucker than the corpulent LA/N, and the serum lipid concentrations of the lean Zucker are lower than those of the lean LA/N. Apoliprotein concentrations were similar and elevated in the two obese genotypes compared to the lean genotypes which were also similar to each other. Male and female obese animals of both strains exhibited hyperinsulinemia under fasting conditions and after oral glucose, with obese male LA/N rats exhibiting the most severe hyperinsulinemia. Glucose tolerance was impaired in obese LA/N animals but was normal in lean rats of both strains and fatty Zucker rats of both sexes. The glucose intolerance observed in obese LA/N animals was more severe in the male than in the female rats. Unlike the corpulent rat, which develops atherosclerotic lesions, the fatty Zucker shows no evidence of advanced vascular lesions on scanning electron microscopy. The fatty Zucker also does not develop the myocardial lesions that are frequent in the male corpulent LA/N rat. It is suggested that the initiation of the atherogenic process is dependent upon elevated insulin levels or transient hyperglycemia. Development of the advanced lesions appears to require the presence of hyperlipidemia.