REGULATION OF GUINEA-PIG VERY-LOW-DENSITY LIPOPROTEIN SECRETION RATESBY DIETARY-FAT SATURATION

We investigated the effects of dietary fat saturation on very low dens ity lipoprotein (VLDL) production in guinea pigs fed semipurified diet s containing 15% (w/w) fat, either corn oil (GO, 58% linoleic acid), l ard (LA, 42% oleic and 24% palmitic acids) or palm kernel oil (PK, 52% lauric and 18% myristic acids) for 4 weeks. Animals were given an int ravenous injection of Triton WR 1339 to block VLDL catabolism and rate s of VLDL triacylglycerol (TAG) and apolipoprotein (ape) B secretion w ere measured over time. Plasma TAG concentrations increased linearly f or 8 h (r = 0.99) and VLDL-TAC secretion rates were significantly high er (P < 0.01) in guinea pigs fed LA (72.7 +/- 14.7 mg/kg-h, n = 12) co mpared to animals fed PK (55.4 +/- 13.4 mg/kg-h, n = 12) or CO (48.6 /- 17.5 mg/kg-h, n = 15). VLDL apoB secretion rates were highest in PK -fed animals (3.1 +/- 1.8 mg/kg-h) compared to guinea pigs fed LA (1.5 +/- 0.8 mg/kg-h) or CO (1.1 +/- 0.6 mg/kg-h) diets (P < 0.005). Concu rrent with analysis of VLDL secretion, turnover of I-125-labeled LDL w as measured. Low density lipoprotein (LDL) fractional catabolic rates were not altered by Triton treatment and LDL apoB specific radioactivi ty (cpm/mu g) did not change over time indicating that: a) the Triton blockage of VLDL catabolism was complete, and b) there was no direct s ecretion of LDL by the liver. These data demonstrate that intake of la rd increases the rate of VLDL-triacylglycerol secretion and that nasce nt VLDL particles from the lard and corn oil diet groups have the same relative triacylglycerol content, whereas palm kernel oil intake incr eases secretion of VLDL particles which have a reduced triacylglycerol content. These results demonstrate that dietary fat chain length and saturation have specific effects on VLDL secretion rates affecting bot h particle number and composition.