A study of the lipid transport system in the cat, Felix domesticus.

Feline serum lipoproteins were fractionated into four distinct classes by density gradient ultracentrifugation and characterized with respect to physical and chemical properties. The distribution of serum lipids, lipoproteins and apolipoproteins was quite unlike that in man, the cat having five times as much high density lipoproteins (HDL) as low density lipoproteins (LDL). The lipoproteins in the d less than 1.019 g/ml fraction of cats were larger and were richer in triglycerides than their human counterparts and contained a considerable amount of beta-migrating particles. The low density lipoproteins of cats and man had similar chemical composition, but cat LDL had a higher negative charge, were smaller and contained apoprotein A-I. Cat HDL consisted of two distinct subfractions HDL2 and HDL3 with similar density boundaries and particle size as in man. In cat serum and HDL fraction apoprotein A-II was a minor component. Like human serum, fasting cat serum contained only the larger species of apoprotein B, apo B-100, whereas intestinal lymph contained exclusively the smaller apo B-48. Post heparin feline and human plasma possessed both lipoprotein lipase and hepatic lipase. Chylomicrons formed after a fat load in cats were removed from the circulation as rapidly as in man. It is concluded, that the cat is another animal model of potential interest for the study of lipoprotein metabolism.