A selective decline of postheparin plasma hepatic triglyceride lipase in hypothyroid rats

The present study aimed to define the effect of thyroid status on two postheparin plasma lipases, i.e., lipoprotein lipase and hepatic triglyceride lipase. Rats with hypo- and hyperthyroidism were used for this purpose. Separate measurement of these two lipases was done by an immunochemical method utilizing antiserum specific to hepatic triglyceride lipase. The 5-wk thyroidectomized, hypothyroid rats had normal plasma concentrations of both triglyceride and cholesterol. These rats showed a selective decline in the activity of postheparin plasma hepatic triglyceride lipase with normal lipoprotein lipase activity. The rats made thyrotoxic by thyroxine treatment had normal plasma levels of both triglyceride and cholesterol. These rats showed normal activities of both hepatic triglyceride lipase and lipoprotein lipase. The observed finding of a selective decline of hepatic triglyceride lipase in hypothyroid rats is discussed in connection with the possible function of this enzyme in lipoprotein metabolism.