DIETARY LINOLEIC-ACID INCREASES AND PALMITIC ACID DECREASES HEPATIC LDL RECEPTOR PROTEIN AND MESSENGER-RNA ABUNDANCE IN YOUNG-PIGS

The present study was conducted to determine tile effects of dietary f atty acids on hepatic LDL receptor (LDLr) protein abundance and mRNA l evels. Sixty pigs were randomized into 10 groups and fed corn-soybean meal diets containing three cholesterol levels (0.25%, 0.5%, and 1.0%, w/w) with no added fat, or fats rich (30% of calories) in palmitic ac id or linoleic acid. A control group was fed the base diet with no add ed fat. After 30 days, plasma LDL-cholesterol (LDL-C) levels increased as the dietary cholesterol increased (P < 0.05); however, there was n o significant effect of either fatty acid. Dietary fatty acids, howeve r, had distinctly different effects on hepatic LDLr protein (analysed by ELISA) and mRNA (analysed by Northern blot) abundance. When pigs co nsumed diets containing 0.25% cholesterol, linoleic acid increased hep atic LDLr protein 40% whereas palmitic acid reduced it 40% (P < 0.05). These changes in LDLr protein abundance were accompanied by parallel changes in hepatic LDLr mRNA; linoleic acid increased LDLr mRNA 2-fold (P < 0.01), whereas palmitic acid decreased it 60 (P < 0.01). The dif ferential effects of fatty acids on LDLr expression were only observed at 0.25% cholesterol, suggesting that higher intakes of cholesterol h ave a dominant and repressive effect on regulation of LDLr expression. Cholesterol intake increased hepatic total cholesterol levels (P < 0. 01) while dietary fatty acids had no effect on hepatic sterols. In sum mary, our results indicate that dietary linoleic acid and palmitic aci d have markedly different effects on hepatic LDLr protein abundance th at are mediated by differential effects on LDLr mRNA levels. Further s tudies are needed to fully elucidate the molecular mechanisms by which fatty acids regulate LDLr mRNA and protein levels.