Studies on serum lipoproteins of rats developing spontaneous hyperlipidemia.

The lipid composition of the serum lipoproteins of Sprague-Dawley rats with varying degrees of hyperlipidemia was investigated. The concentrations of all the lipoproteins were increased with increasing hyperlipidemia. The elevation was found to be more pronounced for very low density VLDL) and low density (LDL) than for high density lipoproteins (HDL). A linear relationship exists between triglyceride and cholesterol contents of VLDL fractions independent of the VLDL level. Eighty to ninety per cent of serum triglycerides are located in the VLDL fraction. Linear relationships were found between the levels of serum triglycerides or VLDL triglycerides and the levels of LDL and HDL cholesterol, respectively. Furthermore, linear relationships exist between total cholesterol content in serum and cholesterol concentration in VLDL, LDL and HDL, respectively. Thus, lipoprotein levels may be estimated by measuring serum cholesterol or triglyceride concentrations. Disk electrophoresis and ultracentrifugation revealed that the LDL fraction (d. 1.006 - 1.063) could be divided into two fractions, which both increase with age. The spontaneous hyperlipoproteinemia of the old rats make these animals suitable as a model for evaluation of drugs against human hyperlipoproteinemia.