Fat emulsions with added free cholesterol or fatty acid cholesteryl esters. Studies on removal mechanisms in vivo and hydrolysis by lipoprotein lipase in vitro.

The fractional elimination rate of fat emulsions of soybean oil, emulsified with egg yolk phosphatides with 1% addition of cholesterol or various cholesteryl fatty acid esters, was studied in rabbits. The fractional removal rate k2%/min was the same after addition of free cholesterol or esters with fatty acids up to eight carbon esters. The k2 values were twice as high for emulsions with cholesteryl-stearate, three times higher with added cholesteryl-palmitate and four times higher when cholesteryl-linoleate was added. The triglyceride (TG) lipase activity was determined with human or rabbit post-heparin plasma and with purified bovine lipoprotein lipase. All these enzyme sources gave similar results. Addition of saturated cholesteryl esters did not affect the lipase activity, but addition of 1% cholesterol markedly decreased the lipase activity. Furthermore, addition of cholesteryl-linoleate and linolenate reduced post-heparin TG lipase activity.