Effect of dietary fat on opiate receptor binding and body composition in mice

C57BL/6 and C3H male mice were fed either a 25% corn oil, 25% butter fat, or chow diet ad libitum for 6 weeks. At that time, opiate receptor binding in the brain and body composition was determined. Regardless of the type of dietary fat, both groups fed with high-fat diets in each strain of mice exhibited obesity in the absence of hyperphagia as compared with their chow-fed counter-parts. Scatchard analysis of opiate receptor binding from the brains of C57BL/6 mice fed with the polyunsaturated fat diet (corn oil) demonstrated a decreased K_D relative to the saturated fat-fed group with no significant difference in B_max. The C3H mice exhibited no significant differences in either binding affinity or receptor number within the three dietary groups. Fatty acid analysis of the synaptic plasma membrane showed changes in the C18:1 ω-9, C18:2 ω-6, and C22:6 ω-3 fatty acid composition. C18:1 ω-9 was elevated while C22:6 ω-3 was depressed in corn oil compared to butter fat-fed C57BL/6 mice. There were no differences in membrane fluidity as measured by fluorescence polarization.