Effect of heparin on the inactivation of serum lipoprotein lipase by the liver in unanesthetized dogs

The injection of heparin into the circulation produces a rapid increase in circulating serum lipoprotein lipase. The lipolysis system apparently circulates as a heparin-apoenzyme complex. Lipoprotein lipase activity disappears from the circulation in an exponential fashion. Available evidence suggests that a major site of removal of lipoprotein lipase activity is the liver. We have evaluated the efficiency of the inactivation system in catheterized unanesthetized dogs by studying the portal vein-hepatic vein difference in lipoprotein lipase activity. Our results demonstrate the high efficiency of the inactivation system in vivo. The results of this study also show that high levels of heparin can block the inactivation system and suggest a possible two-step mechanism. The first step in inactivation may involve the destruction of heparin by a liver heparinase. This step may induce dissociation of the active complex. After dissociation, the apoenzyme is apparently removed in a second step.