FISCHER-344 RATS ARE THE SAME WEIGHT BUT ARE FATTER THAN S5B P1RAS RATS FED A HIGH-FAT DIET/

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 fe d a high-fat diet for 10 weeks until sacrifice. Body wt and length, fo od intake, fat depot and muscle weights, body composition and serum tr iglycerides, cholesterol, glucose, insulin, and insulin-like growth fa ctor-I (IGF-I) concentrations were determined. Body weights were simil ar 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 bo dy fat in S5B rats was 16 +/- 1%. Differences were significant. Indivi dual 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 carca ss, was 30% greater in S5B than in Fischer 344 rats while the other tw o strains were intermediate. The same was true for muscle mass. Fische r 344 and SD rats fed a high fat diet were hyperinsulinemic whereas me an serum insulin concentrations were normal in S5B and OM rats. Fische r 344 rats had significantly lower serum glucose concentrations than O M rats but there were no other strain differences. Serum triglyceride, cholesterol and IGF-I concentrations were similar for the 4 strains.