Abstract
Inbred strains of rats are excellent models to study genetics of diet-induced obesity. Six weanling rats from each of 4 strains, S5B P1Ras (S5B), Fischer 344, Osborne-Mendel (OM) and Sprague-Dawley (SD) were fed a high-fat diet for 10 weeks until sacrifice. Body wt and length, food intake, fat depot and muscle weights, body composition and serum triglycerides, cholesterol, glucose, insulin, and insulin-like growth factor-I (IGF-I) concentrations were determined. Body weights were similar for S5B and Fischer 344 rats and both strains weighed significantly less than OM or SD rats. Fischer 344 and S5B rats also consumed less food than OM or SD rats. However, S5B rats utilized significantly more energy than the other strains rather than storing it as body fat. In Fischer 344, OM and SD rats, body fat ranged from 25 to 31% whereas body fat in S5B rats was 16 ± 1%. Differences were significant. Individual white fat depots weighed from 150 to 400% more in Fischer 344, OM and SD rats than in S5B rats. Body protein, expressed as g/100g carcass, was 30% greater in S5B than in Fischer 344 rats while the other two strains were intermediate. The same was true for muscle mass. Fischer 344 and SD rats fed a high fat diet were hyperinsulinemic whereas mean serum insulin concentrations were normal in S5B and OM rats. Fischer 344 rats had significantly lower serum glucose concentrations than OM rats but there were no other strain differences. Serum triglyceride, cholesterol and IGF-I concentrations were similar for the 4 strains.
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