Lipoprotein Lipase Activity in Adipose Tissue and in Postheparin Plasma in Human Obesity

The mechanism by which obesity influences the metabolism of circulating triglycerides was assessed by determination of lipoprotein lipase (LPL) activity in adipose tissue and in postheparin plasma of 26 normolipidemic obese and 26 normal-weight subjects. Furthermore, the uptakes of VLDL triglyceride and FFA by adipose tissue in vitro were measured in these two groups. The heparin-releasable LPL activity per weight unit of adipose tissue was similar in obese and normal-weight subjects but the LPL activity per fat cell was on an average twice as high in obese as in non-obese subjects. Also the VLDL triglyceride and FFA uptakes by adipose tissue were similar in obese and non-obese groups when related to tissue weight but both were increased in obese fat cells compared with those of non-obese. When expressed per total body fat, all these parameters of adipose tissue lipid uptake were higher in obese than in normal-weight subjects. In contrast, the obese group did not show any increase in the postheparin plasma LPL activity but rather a tendency for the values to accumulate in the low normal range. Serum triglyceride concentration was not related to any of the LPL activities or to tissue lipid uptake in separate or combined obese and non-obese groups. Serum basal insulin level and insulin response to glucose were significantly higher in the obese than in non-obese subjects but in spite of this, the serum triglyceride level was similar in the two groups. Stepwise multiple regression analysis showed that all the measured parameters of adipose tissue were positively correlated to fat cell size but when the latter was held constant, the fat cell VLDL triglyceride uptake was still related to cell LPL activity and to serum insulin concentration. These results suggest that in obesity the adipose tissue has an increased capacity to remove circulating triglycerides.