DIETARY-FAT SATURATION AND CHAIN-LENGTH MODULATE GUINEA-PIG HEPATIC CHOLESTEROL-METABOLISM

The effects of dietary fat saturation and saturated fatty acid composi tion on plasma lipoprotein concentrations and hepatic cholesterol meta bolism were investigated in guinea pigs. Animals were fed semipurified diets containing 15 g fat/100 g diet, as palm kernel, palm oil, beef tallow, lard, olive oil or corn oil. Plasma lipoprotein concentrations were significantly altered by the type of dietary fat. The LDL choles terol concentration was highest in animals fed the diet with palm kern el and lowest in animals fed the diet with corn oil, whereas HDL chole sterol was lowest in beef tallow-fed guinea pigs (P < 0.01). Hepatic c holesteryl ester concentrations were 100% higher in animals fed diets containing polyunsaturated corn oil and monounsaturated olive oil comp ared with animals fed any of the saturated fat diets (P < 0.01). Hepat ic 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase activity varied in the different dietary fat groups independent of hepatic chol esterol pools or plasma LDL. concentrations. In contrast, hepatic acyl -CoA: cholesterol acyltransferase (ACAT) activity was significantly co rrelated with plasma LDL cholesterol across all dietary groups (r = 0. 63, P < 0.001). These data demonstrate that regulation of hepatic HMG- CoA reductase activity is relatively independent of changes in plasma lipoprotein levels, whereas hepatic ACAT activity exhibits a positive correlation with plasma LDL cholesterol concentrations.