DIETARY SATURATED FATTY-ACID COMPOSITION HAS DIFFERENTIAL-EFFECTS ON HDL BINDING TO GUINEA-PIG HEPATIC MEMBRANES

The effects of dietary saturated fatty acid composition on high densit y lipoprotein (HDL) metabolism in guinea pigs were investigated. Anima ls were fed semi-purified diets containing 15% (w/w) fat, either palm kernel oil (PK), high in lauric + myristic acids; palm oil (PO), high in palmitic acid; or beef tallow (BT), high in stearic acid. Intake of the PK diet resulted in the highest plasma total cholesterol level (P < 0.001) whereas plasma HDL levels were lowest with the BT diet (P< 0. 01). Values were 10.3 +/- 2.4, 9.1 +/- 1.5 and 7.3 +/- 1.0 mg/dL (n = 9) for animals fed PK, PO and BT respectively. While there were no dif ferences in hepatic cholesteryl ester concentrations, hepatic free cho lesterol levels were significantly decreased in animals fed the PO die t (P< 0.01). In contrast, cholesterol levels of muscle and adipose wer e highest in animals fed the PO diet (P< 0.05). Adipose tissue fatty a cid composition reflected dietary fatty acids. Apolipoprotein E-free H DL binding to hepatic membranes was determined using I-125-HDL. While no differences in receptor affinity (K-d) due to dietary fat compositi on were found, HDL binding protein number (B-max) was highest in anima ls fed the BT diet (2.39 +/- 0.05 mu g/mg), intermediate in the PK(1.9 8 +/- 0.07 mu g/mg) and lowest in the PO group (1.69 +/- 0.07 mu g/mg) (P < 0.01). A significant negative correlation was found between plas ma HDL levels and hepatic membrane HDL binding protein number (B-max) (r = -0.59, n = 18, P < 0.01) for the three dietary fat groups. These data demonstrate that changes in dietary saturated fatty acid composit ion have differential effects on plasma HDL levels which appear relate d to changes in the capacity of hepatic membranes to bind HDL.