LIPOPROTEIN-LIPASE MASS AND ACTIVITY IN PLASMA AND THEIR INCREASE AFTER HEPARIN ARE SEPARATE PARAMETERS WITH DIFFERENT RELATIONS TO PLASMA-LIPOPROTEINS

Lipoprotein lipase (LPL) activity and mass in plasma and their increas e after heparin administration were measured in 61 men who had suffere d myocardial infarction before the age of 45 years and in 69 populatio n-based age- and sex-matched control subjects without coronary heart d isease to study the relations between these parameters in plasma and t heir correlations with plasma lipoproteins in subjects with a wide ran ge Of lipoprotein and LPL levels. There was a relatively large amount of LPL protein compared with LPL activity in preheparin plasma, indica ting that the majority of circulating LPL is catalytically inactive. L PL mass and activity in postheparin plasma (postheparin minus prehepar in values) were highly correlated. and the calculated mean specific ac tivity (0.35 mU/ng) was in the range expected for catalytically active LPL. Hence, heparin releases mainly active LPL. The four LPL paramete rs (mass and activity in plasma and their increase after heparin admin istration) were not related to each other: except for postheparin plas ma LPL mass and activity, and they showed different correlations with plasma lipoprotein lipid concentrations. There was a strong positive c orrelation between LPL mass in preheparin plasma and the HDL cholester ol level as well as weak negative relations to VLDL triglyceride and c holesterol concentrations in the patients. In contrast, preheparin LPL activity showed no correlation with the HDL cholesterol level but wea k positive relations to VLDL triglyceride and cholesterol concentratio ns in the control subjects. Postheparin plasma LPL activity related po sitively to the HDL cholesterol level and negatively to the VLDL trigl yceride concentration in the control subjects. Case subjects differed from control subjects in that they had higher preheparin plasma LPL ac tivity and a tendency toward lower specific activity of postheparin pl asma LPL. The different relations of the measured LPL parameters to pl asma lipoproteins and the difference in preheparin plasma LPL activity between patients and control subjects might reflect a disturbance of the LPL system in the patients.