| Abstract: | It was recently noted that newborn mice have much higher lipase activity in plasma than rats or humans, and that most of the activity is due to an enzyme related to the hepatic (heparin-releasable) lipase. Here we report that this lipase is present in plasma of adult mice also. In contrast to the high activity of hepatic lipase, the activity of lipoprotein lipase in plasma was low and similar to that in rats. The source of the plasma lipase was probably the liver, since we could not demonstrate hepatic lipase-like activity in any other organ. When human hepatic lipase was injected into mice, it rapidly disappeared from plasma. Most of the injected lipase located in the liver, and could be released back into circulation by injection of heparin. These results indicate that there are binding sites for hepatic lipase in mouse liver, and suggest that mouse hepatic lipase has an affinity for these sites which is lower than usual. It is currently believed that the endothelial acceptors are heparan-sulfate or similar molecules. Mouse hepatic lipase eluted from heparin-Sepharose at lower salt concentration than rat or human hepatic lipase, demonstrating that it has a relatively low affinity for heparin-like polysaccharides. |
