Differential effects of dietary fat on chick plasma and liver composition and HMG-CoA reductase activity

The comparative effects of diet supplementation with 10% saturated fat rich in 12:0 and 14:0 fatty acids (coconut oil), without and with 1% added chol esterol and with 10% unsaturated fat rich in n-3 polyunsaturated fatty acid s (menhaden oil) on cholesterol metabolism in neonatal chicks were examined to clarify the different mechanisms of their hyper- and hypolipidemic acti on. Supplementation of coconut oil produced a significant hypercholesterole mia after 7 days of treatment, with a similar increase in the amount of bot h free and esterified cholesterol. Supplementation of coconut oil plus chol esterol produced a higher increase of plasma cholesterol levels (approximat ely two to three rimes higher than those found with standard diet). However , supplementation of menhaden oil induced a significant decrease in total c holesterol after only 2 weeks of treatment. Levels of plasma triglycerides did nor change by coconut oil addition to the diet, bur a significant incre ase was observed after coconut oil plus cholesterol feeding. Menhaden oil p roduced a transient decrease in plasma triglycerides. Hepatic 3-hydroxy-3-m ethylglutaryl-CoA reductase activity did not change with coconut oil treatm ent. However, both coconut oil plus cholesterol and menhaden oil supplement ed diets drastically decreased reductase activity after 1 week of dietary m anipulation. These results show that different nutrients with the same inhi bitory effect on reductase activity produced opposite effects on plasma cho lesterol content, suggesting the existence of important differences in the regulatory mechanisms implied in cholesterol biosynthesis and its accumulat ion in plasma. (C) Elsevier Science Inc. 1999. All rights reserved.