Dietary fish oil decreases VLDL production rates.

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 less than 0.03) and 49% lower (P less than 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 less than 0.01), but there were no differences seen in Km or Vmax 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 less than 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 less than 0.025) and 38% (P less than 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 less than 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 less than 0.01).