In Vitro Studies of Human Plasma Lipolytic Activity Before and After Oral Fat Intake

¹ From the Division of Laboratories, Cedars of Lebanon Hospital, Los Angeles, California

The rate of in vitro lipolysis of added human low density lipoproteins was determined in 22 normal individuals using fasting and lipemic plasma. Unesterified fatty acid release was found in 16 subjects in all, in 10 in the fasting plasma and in 14 in the postlipemic plama. Lipolytic activity was greater in the lipemic sample in eight of the 16 individuals, in three it was unchanged before or after fat intake, and in five it was higher in the fasting sample. Addition of deoxycholate, which decreases heparin clearing factor and increases pancreatic lipase activity, inhibited lipolysis in most of the subjects and increased it in a few. Studies using beta-naphthol laurate, which in the presence of taurocholate is an excellent substrate for human pancreatic lipase but not for postheparin lipolytic activity, showed no hydrolysis in eight subjects, in six of whom lipolysis of the lipoproteins occurred. The results of the study suggest that increased plasma lipolytic activity is sometimes present after the ingestion of fat. They further indicate that endogenous heparin lipoprotein lipase is the major plasma enzyme involved in the splitting of neutral fat, but that a lipase similar to pancreatic lipase may be present less frequently, in small amounts, and may require added bile for activity.