Effect of pancreatic phospholipase A2 and gastric lipase on the action of pancreatic carboxyl ester lipase against lipid substrates in vitro

Preincubation of a triolein/phospholipid/cholesteryl oleate-emulsion in vitro with either pancreatic phospholipase A2 (PLA2) or gastric lipase (GL) resulted in hydrolysis (measured by pH-stat-titration) of cholesteryl [3H]oleate only after human pancreatic carboxyl ester lipase (CEL) was added to the system. No appreciable hydrolysis was observed when CEL was added alone. Consequently, a concerted action either of PLA2 and CEL or of GL and CEL made the substrate cholesteryl oleate available for hydrolysis by CEL. This was the case when cholesteryl oleate was solubilised in a phospholipid-stabilised triglyceride emulsion, which is the physico-chemical form in which the major part of dietary cholesteryl esters are presented to the gastro-intestinal tract of man.