Two methods compared for measuring lipase activity in plasma after heparin administration.

We compared two methods for the direct selective measurement of hepatic lipase and lipoprotein lipase activities in human plasma after intravenous administration of heparin. Except for the emulsifier (gum arabic vs lecithin), the two assay media for hepatic lipase are essentially similar. Results for hepatic lipase by these two assays correlate well (r = 0.99). The assays for lipoprotein lipase in the two procedures differ in the way that hepatic lipase activity is eliminated (immunological inhibition vs a specific substrate emulsion), and also with regard to the emulsifier. The substrate emulsion stabilized by gum arabic (immunological assay) consistently yielded about three times higher enzymic activity than the specific substrate stabilized by lecithin. Experiments in which purified enzymes were used demonstrated that this systematic difference can be accounted for by the different emulsifiers. The satisfactory correlation (r = 0.92) between the two lipoprotein lipase assays, however, demonstrates that they measure the same enzymic activity.