Dietary fish oil decreases VLDL production rates

Abstract

The purpose of the study was to evaluate whether the hypocholesterolemic effect of fish oil in roosters (10% fish oil vs. 10% corn oil in the diet) is due to a decrease in very-low-density lipoprotein (VLDL) secretion rate. Previous studies have shown that in vivo inhibition of lipoprotein lipase with a specific antiserum quantitatively blocks VLDL catabolism. Secretion of VLDL cholesterol and triacylglycerol in fasting roosters was measured during a 4 h inhibition of lipoprotein lipase. Secretion rates of VLDL cholesterol and triacylglycerol were 39% lower ( P < 0.03) and 49% lower ( P < 0.025), respectively, with the fish oil diet. VLDL composition at the end of the inhibition was not remarkably different between treatments. Smaller portomicrons were produced by fish oil feeding ( 1737 ± 120 vs. 2090 ± 64 A ̊ , P < 0.01 ), but there were no differences seen in K m or V max when portomicrons were incubated with purified avian lipoprotein lipase. Plasma cholesterol and triacylglycerol levels were not affected by the oil supplements. In a second study, the diets were supplemented with 0.5% cholesterol in addition to the oils. Fasting serum cholesterol was 52% lower ( P < 0.05) in the fish oil-fed birds, most of the difference being in the VLDL fraction (11.5 ± 9 vs. 99.7 ± 66 mg/ dl). Low-density lipoprotein cholesterol was also significantly lower. VLDL cholesterol and triacylglycerol secretion rates were lower by 39 ( P < 0.025) and 38% ( P < 0.06), respectively, in the fish oil group. VLDL from fish oil-fed birds collected after a 4 h inhibition had a lower cholesterol content than that from the corn oil-fed birds (15.9 ± 2.8 vs. 21.2 ± 1.9 wt%, P < 0.025). In the fish oil-fed animals the decrease in VLDL cholesterol secretion accounted for 61% of the observed decrease in VLDL cholesterol. The balance of the decrease in plasma VLDL cholesterol was due to a significant increase in VLDL cholesterol fractional removal rate in the fish oil-fed animals from 0.45 ± 1.0 to 2.63 ± 1.7 h −1 ( P < 0.01).