Effects of Triton WR 1339 and Heparin on the Transfer of Surface Lipids from Triglyceride-rich Emulsions to High Density Lipoproteins in Rats

The influence of lipolytic mechanisms on the transfer of phospholipids and unesterified cholesterol from artificial emulsions, serving as chylomicron models to other plasma lipoproteins, mainly high density lipoproteins (HDL) were tested in vivo. The emulsions labeled with radioactive lipids were injected into the bloodstream of rats (controls) and the results were compared with those obtained from rats that had previously been treated with Triton WR 1339 or heparin. Plasma clearance and the distribution of cholesteryl esters, phospholipids and unesterified cholesterol in the different plasma lipoprotein fractions were then determined. Whereas virtually no cholesteryl esters were found in d greater than 1.006 g/mL density fraction of the three experimental groups, 2.8 +/- 1.3% of the injected phospholipids were in the 1.063-1.210 g/L density fraction of the Triton treated rats, and 12.6 +/- 5.4% of the heparin treated rats, as compared to 10.1 +/- 1.7% in controls. This indicates that lipolysis directly influences phospholipid transfer to HDL. In contrast, free-cholesterol transfer to HDL, besides being less pronounced than phospholipid transfer, was enhanced by Triton and diminished by heparin, indicating that lipolytic mechanisms were not important determinants in this process.