The role of insulin in the regulation of human adipose tissue lipoprotein lipase was evaluated. Adipose tissue heparin-releasable lipoprotein lipase (thought to be related to peripheral clearance of plasma triglycerides) was low in insulin-deficient, untreated hyperglycemic diabetic subjects (P less than 0.001) and treatment of hyperglycemia returned the activity to normal. In chronic hyperinsulinism, represented by obesity, heparin-releasable activity among control subjects was correlated to percent of ideal body weight (r=0.53, P less than 0.05) and to fat cell size (r=0.61, P less than 0.02). Acetone-ether powder lipoprotein lipase activity (presumed to reflect total tissue enzyme) was also related to percent of ideal body weight (r=0.76, P less than 0.001 for controls; r=0.67, P less than 0.05 for diabetics) and to fat cell size (r=0.71, P less than 0.01 for controls; r=0.85, P less than 0.01 for diabetics. Postprandial-stimulated insulin secretion was related to diet-induced changes in lipoprotein lipase in control subjects; both were dependent upon the amount of dietary carbohydrate. In contrast, the diabetic patients with low insulin responses, failed to increase lipoprotein lipase activity with feeding. The changes in heparin-releasable (r=0.66, P less than 0.01) and acetone-ether powder (r=0.69, P less than 0.01) activity during feeding were related to the percent increase in plasma insulin. Thus, insulin appears to be important in the regulation of human adipose tissue lipoprotein lipase activity. Elevated insulin levels in obesity and increased insulin secretion after eating were associated with increased lipoprotein lipase activity. Defects in insulin secretion, both in postabsorptive and postprandial states, are associated with low adipose tissue lipoprotein lipase and may lead to hypertriglyceridemia in diabetic man.
O J Pykälistö, P H Smith, J D Brunzell