Effect of cholesterol feeding on apo B and apo E concentrations and distributions in euthyroid and hypothyroid rats

Lipoprotein profiles in experimental hypercholesterolemia were studied using euthyroid and hypothyroid cholesterol-fed rats. In both groups, serum cholesterol concentration increased, but to a lesser extent in the cholesterol-fed euthyroid rats, with similar changes in distribution among lipoprotein fractions in both groups. Agarose electrophoresis of plasma and individual lipoprotein fractions showed that beta-VLDL and HDLc were present in the hypothyroid, cholesterol-fed rats. In the euthyroid and hypothyroid cholesterol-fed rats, serum apo B concentrations increased three-fold and five-fold, respectively. This reflected increases of apo B in very low density and intermediate density lipoproteins. In the euthyroid cholesterol-fed rat, serum apo E decreased 50%, while the serum apo E concentration was not significantly changed in hypothyroid cholesterol-fed rats. In both the euthyroid and the hypothyroid cholesterol-fed rats, apo E decreased in high density lipoproteins and increased in lower density lipoproteins. We observed qualitative and quantitative differences between hypothyroid and euthyroid cholesterol-fed rats. The major qualitative differences were the appearance of beta migrating very low density lipoproteins (beta-VLDL) and HDLc in the hypothyroid cholesterol-fed rat, and a decrease of serum apo E concentrations in the euthyroid cholesterol-fed rats. Changes in serum cholesterol and apo B concentrations and the distribution of cholesterol, apo B, and apo E among the lipoprotein fractions were similar in direction in both groups, but greater in magnitude in the hypothyroid versus euthyroid cholesterol-fed rats. These data demonstrate that hypothyroidism should be considered when evaluating apolipoprotein changes in hypercholesterolemic animal models.