REGULATION OF VERY-LOW-DENSITY LIPOPROTEIN APO-B METABOLISM BY DIETARY-FAT SATURATION AND CHAIN-LENGTH IN THE GUINEA-PIG

Studies investigated the effects of dietary fatty acid composition and saturation on the regulation of very low density lipoprotein (VLDL) a po B flux, clearance, and conversion to low density lipoprotein (LDL) in guinea pigs fed semipurified diets containing 15% (w/w) corn oil (C O), lard (LA), or palm kernel oil (PK). Plasma cholesterol levels were highest with dietary PK (3.1 +/- 1.0 mmol/L) followed by LA (2.4 +/- 0.4 mmol/L) and CO (1.6 +/- 0.4 mmol/L) intake. VLDL particles were la rger (P < 0.05) in the LA (78 +/- 7 nm) and PK (69 +/- 10 nm) groups c ompared to animals fed CO (49 +/- 5 nm). VLDL-apo B fractional catabol ic rates (FCR) were highest in guinea pigs fed the LA diet (P < 0.05) and VLDL apo B flux, estimated from VLDL I-125-apo B turnover kinetics , were higher in LA compared to PK or CO fed guinea pigs. in the case of PK consumption, the kinetic estimates of VLDL apo B flux significan tly underestimated rates compared to direct VLDL apo B secretion measu rements and LDL turnover analyses. These data demonstrate that differe nces in the composition and amount of saturated fatty acids have diffe rential effects on VLDL apo B flux, catabolism, and conversion to LDL which, together with changes in LDL receptor-mediated catabolism deter mine plasma LDL cholesterol levels in guinea pigs. The data also indic ate that kinetic analysis of VLDL metabolism in PK fed animals is inac curate possibly due to the presence of a small, nonequilibrating pool of newly synthesized VLDL which is rapidly converted to LDL.