The origin and fate of HDL.

High density lipoproteins are synthesized both in the liver and intestine. All apoproteins can be synthesized in the liver and intestine except the "C" apoproteins which could not be synthesized by the intestine. After injection of 125I-HDL its different apoproteins are removed from the circulation at a similar rate. Most of the HDL is removed by the liver and the degradation of the protein moiety of HDL was localized to the lysozomes of the parenchymal cells. Cholesterol feeding alters the distribution of lipoprotein fractions and results in the appearance of a new intermediate density class, in which all HDL apoproteins are present in addition to apo-B. Cholesterol feeding also results in an alteration of apoprotein composition of HDL.