The effect of estrogen on the lipoprotein lipase activity of rat adipose tissue

Abstract

The effect of 17β estradiol or progesterone administration on adipose tissue lipoprotein lipase activity was studied in male and ovariectomized female rats. Lipoprotein lipase activity was measured in acetone ether extracted preparations of adipose tissue with doubly labeled (14C fatty acid, 3H glyceryl) chylomicron triglyceride as substrate. Administration of 17β estradiol to male rats lowered adipose tissue lipoprotein lipase activity from 8.22±1.8 U/g (1 U = 1 μmol triglyceride hydrolyzed per Hr) to 4.96±0.5 U/g in the treated group. Ovariectomy increased adipose tissue lipoprotein lipase activity from 10.4±1.8 U/g in controls to 22.7±4.3 U/g. 17β estradiol administration to ovariectomized rats caused a marked fall in adipose tissue lipoprotein lipase activity: 17β estradiol (2.5 μg/day) lowered the enzyme activity to 9.00±1.2 U/g, whereas 25 μg/day further decreased lipoprotein lipase activity to 3.2±0.6 U/g. Blood triglyceride levels increased from 0.8±0.05 μmol/ml in ovariectomized rats to 1.4±0.09 μmol/ml in 25 μg/day 17β estradiol treated rats. Progesterone administration did not affect adipose tissue lipoprotein lipase activity in either male or ovariectomized rats. Heart and lung lipoprotein lipase activity was unaffected by hormone treatment. The authors suggest that the rise in blood triglyceride concentrations, which accompanies high plasma estrogen levels, could be due to the marked inhibition of adipose tissue lipoprotein lipase activity.