Liver and extrahepatic contributions to postheparin serum lipase activity of the rat

The influence of the amount of heparin injected on the contributions of liver and of extrahepatic tissues to the lipase activity of postheparin serum of the rat was studied. It was found that when high doses of heparin (20 I.U./100 g bodyweight) were injected, the liver contributes for 63% to the total triacylglycerol lipase activity of postheparin serum. At low heparin levels (0.4 I.U./100 g bodyweight) the lipase activity in the postheparin serum is almost solely derived from the extrahepatic tissues. The activity of the liver enzyme in the postheparin serum was found to increase very fast after heparin injection. 2 min after heparin injection a maximum activity of the liver enzyme in the serum was found. Subsequently the liver enzyme is removed from the circulation. Not only the activity of the liver enzyme is dependent on the amount of heparin injected, but also the amount of enzyme released from the liver. Fat feeding increases the hydrolytic activity released from the liver by heparin. Immunological studies suggest that the enzyme may be in a more active state. The role of the heparin-releasable liver enzyme in fat metabolism is discussed.