HIGH-DENSITY-LIPOPROTEIN METABOLISM IS ALTERED BY DIETARY-CHOLESTEROLBUT NOT FAT-SATURATION IN GUINEA-PIGS

To study dietary fat and cholesterol effects on plasma high density li poprotein (HDL) metabolism and rates of apolipoprotein (ape) A-I catab olism, guinea pigs were fed 15% (wt/wt) lard- or corn oil-based diets with 0.01%(basal), 0.08%, 0.17% or 0.33% cholesterol. Absorbed dietary cholesterol provided 6%, 50%, 100% and 200%, respectively, of the dai ly endogenous cholesterol synthetic mass. While total plasma cholester ol concentrations increased significantly above basal levels at the 0. 17% and 0.33% cholesterol intakes, plasma apo E-free HDL (E(o)HDL) cho lesterol concentrations did not increase significantly until the 0.33% cholesterol level (P < 0.001). Fractional catabolic rates (FCR) of in jected [I-131]-apo A-I were not altered by dietary treatment, either f at saturation or cholesterol, but were inversely correlated with plasm a E(o)HDL cholesterol levels (r = -0.622), suggestive of a regulatory role of turnover rates on HDL cholesterol levels independent of dietar y treatment. Analysis of the high affinity E(o)HDL binding to isolated hepatic membranes suggested that hepatic binding was not a determinan t of HDL catabolism, as dietary cholesterol-induced decreases in B-max (binding capacity) were not correlated with changes in apo A-I FCR. E ven though dietary cholesterol was associated with increased plasma E( o)HDL cholesterol and with decreased HDL binding protein B-max, these values did not correlate with each other nor with effects on apo A-I F CR.