Postheparin plasma contains two separate lipolytic enzymes, lipoprotein lipase and hepatic lipase, which are released from vascular endothelial cells. The former is located in extrahepatic capillary beds and has a well-defined role in the catabolism of plasma triglycerides. The hepatic lipase has been recently shown to be located on the surface of hepatic endothelial cells [l] but the physiological function of this enzyme is still far from clear. Hepatic endothelial lipase can hydrolyze chylomicron and VLDL triglycerides in vitro [2] but its activity in postheparin plasma has no correlation to plasma triglyceride levels [3]. It has been suggested that hepatic lipase could be involved in the uptake of chylomicron remnants [4], intermediate density lipoprotein [5] or LDL [6] by the liver but there is little experimental evidence for any of these possibilities.

We have recently purified the heparin-releasable lipase from rat liver perfusates [7] and used the enzyme preparation for production of antiserum. The availability of this anti-hepatic lipase serum offered a good opportunity to study the function of the enzyme by searching whether plasma lipoproteins are influenced by specific inhibition of the hepatic endothehal lipase in vivo.