Lipase activity in the human aorta.

The hydrolysis of triglycerides by grossly normal male human aortas has been studied in vitro. The tissue contains an acid lipase (pH optimum, 5.4) and an alkaline lipase (pH optimum, 8.8). Both lipases catalyze the hydrolysis of saturated triglycerides; the rate decreases with increasing fatty acyl chain from C(10) to C(18). Glycerol trioleate, trilinoleate, and trilinolenate are hydrolyzed at similar rates. Alkaline lipase is inhibited about 50% at 7.2 mm glycerol trioleate, while acid lipase is unaffected at this concentration. Both lipases are activated by Ca(++) ions. The acid lipase is easily inactivated by deionized water used either as a homogenizing or dialyzing medium. Acid lipase is strongly inhibited by BSA, sodium deoxycholate, and sodium taurocholate; alkaline lipase is unaffected by BSA and is activated about twofold by bile salts. The products of hydrolysis of glycerol trioleate by aortic lipases are predominantly oleic acid and glycerol 1,2-dioleate with a small accumulation of glycerol monooleate. The aortic preparations appear to contain inhibitors for both the acid and alkaline lipase. The substance which inhibits alkaline lipase also inhibits pancreatic lipase; it is heat-stable and dialyzable. The inhibitor of the acid lipase is also heat-stable but is nondialyzable.