Hepatic triglyceride lipase is not an insulin-dependent enzyme in rats

The aim of this study is to examine whether insulin regulates the activity of hepatic triglyceride lipase. The activities of both hepatic triglyceride lipase (H-TGL) and lipoprotein lipase (LPL) were measured in plasma after intravenous administration of heparin. Insulin-deficient diabetic rats had normal H-TGL activity. Insulin-treated normal rats had no different enzyme activities from those of controls. Ventromedial hypothalamic (VMH) lesioned rats that became obese and showed hyperinsulinemia, had also normal enzyme activities. From these experiments, it is concluded that H-TGL is not an insulin-dependent enzyme. As far as LPL is concerned, this enzyme was increased in both insulin-treated rats and rats with VMH lesions. This was consistent with the established fact that insulin has a stimulatory effect on adipose tissue LPL. The LPL activity in postheparin plasma was not decreased in insulin-deficient rats. It is speculated that a possible increase in muscle LPL compensated for the low adipose tissue LPL in diabetic rats.