Cholesterolemic Rabbit Lipoproteins: Serum Lipoproteins of the Cholesterolemic Rabbit

Abstract

The chemical composition of the low density lipoproteins (S_f 0 to 25. S_f 15 to 100, and S_f 20 to 400) has been investigated by isolating the molecules centrifugally and separating the various lipid constituents on silicic acid columns and analyzing the fractions so obtained by infrared spectrophotometry. Quantitative protein determinations were also made upon each group of lipoproteins. The molecules are shown to contain 40–60% cholesterol esters, 10–20% unesterified cholesterol, 10–20% phospholipid, and 3–30% protein, depending upon the sedimentation characteristics. The quantity of glyceride was usually less than 10% for all of the above mentioned groups of lipoproteins. The quantity of unesterified fatty acids was always less than 6%. Two of the four animals from which samples were withdrawn and analyzed had previously received daily heparin injections for a period of 10 weeks. The effects of heparin injections upon the ultracentrifugal patterns of a larger group of rabbits was also studied. No significant changes in the concentrations of the S_f 5 to 15, S_f 15 to 40, and S_f 40 to 100 species of lipoproteins were found which could be attributed to the heparin injections. The major peak, usually to be found in the S_f 5 to 15 region, did show a small but significant decrease in sedimentation coefficient in response to heparin injection. Serum from all of the animals receiving heparin did show a definite lipolytic activity in vitro.