The inhibition of in vivo of lipoprotein lipase (clearing factor lipase) activity by Triton WR 1339

Lipoprotein lipase activity was measured in heart homogenates and in heparin releasable and nonreleasable fractions of isolated perfused rat hearts, after the intravenous injection of Triton WR 1339. In homogenates of hearts from starved rats, lipoprotein lipase activity was significantly inhibited (P<0.001) 2h after the injection of Triton. This inhibition was restricted exclusively to the heparin releasable fraction. Maximum inhibition occurred 30 min after the injection and corresponded to about 60% of the lipoprotein lipase activity that could be released from the heart during 30s perfusion with heparin. Hearts of Triton treated starved rats were unable to take up and utilize ¹⁴C labelled chylomicron triacylglycerol fatty acids, even though about 40% of heparin releasable activity remained in the hearts. It is concluded that Triton selectively inhibits the functional lipoprotein lipase, i.e. the enzyme directly involved in the hydrolysis of circulating plasma triacylglycerols. Lipoprotein lipase activities measured in homogenates of soleus muscle of starved rats and adipose tissue of fed rats were decreased by 25 and 39% respectively after Triton injection. It is concluded that, by analogy with the heart, these Triton inhibitable activities correspond to the functional lipoprotein lipase.