A role for hepatic lipase in chylomicron and high density lipoprotein phospholipid metabolism

The rate of removal of phosphatidylethanolamine and phosphatidylcholine from the plasma of rats treated with antiserum to hepatic lipase was measured. The hepatic lipase antiserum was injected intravenously into animals prior to injection of 32P-labeled chylomicrons or 32P-labeled high density lipoproteins. In experiments in which 32P-labeled chylomicrons were injected, antiserum treatment inhibited removal of [32P]phosphatidylethanolamine from chylomicrons, and the unlabeled serum phosphatidylethanolamine levels increased 2-2.5-fold in 30 min. In contrast, hepatic lipase antiserum had no significant effect on the clearance of chylomicron [32P]phosphatidylcholine or on unlabeled phosphatidylcholine concentrations in serum after injection of chylomicrons. In experiments in which 32P-labeled high density lipoproteins were injected, the inhibitory effect of the antiserum on the rapid removal of [32P]phosphatidylethanolamine from the circulation was even more marked than its effect on the removal from chylomicrons. The removal of high density lipoprotein phosphatidylcholine on the other hand was unaffected by the antiserum, although a moderate increase in serum phosphatidylcholine concentration was seen. In antiserum-treated rats injected with 32P-labeled chylomicrons or high density lipoproteins, hepatic [32P]phosphatidylethanolamine radioactivity was decreased. Significantly more [32P]phosphatidylethanolamine was recovered from blood plus liver in the antiserum-treated rats, indicating that the antiserum inhibited the overall degradation of injected [32P]phosphatidylethanolamine. The data suggest that phosphatidylethanolamine is a preferred substrate for hepatic lipase in the metabolism of chylomicron and high density lipoprotein phospholipid.