Weanling male Sprague-Dawley rats were fed one of 10 purified, high fat (20% wt/wt) diets for 6 wk to determine if an in vivo relationship exists between dietary fat composition, plasma membrane composition and insulin binding to epididymal adipocytes. The diets fed provided ratios of polyunsaturated to saturated fatty acids (P/S ratios) representative of those consumed by the human population and ranging from 0.14 to 1.80. The dietary P/S ratio fed altered the essential and nonessential fatty acid composition of plasma membrane phospholipids. Diet induced alterations in membrane phosphatidylcholine and phosphatidylethanolamine composition were found to be related in a dose-dependent manner to insulin binding at both physiological and supraphysiological insulin concentrations. This observation further supports in vivo a dietary mechanism for modulating insulin action. The present study establishes that the effect of diet on the relationship between membrane composition and insulin binding reaches a plateau within the physiological range of dietary P/S ratios.
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