Lipolytic Activity of Human Gastric and Duodenal Juice Against Medium and Long Chain Triglycerides

Abstract

The presence of lipase in gastric aspirates containing less than 3 % contamination with duodenal reflux (as determined by tests for bile acid) was demonstrated in all samples of apparently normal gastric juice from 73 subjects when assayed with a trioctanoin substrate emulsified in sodium taurodeoxycholate and buffered at p H 6. This enzyme, in contrast to lipase(s) in duodenal aspirate, was stable at p H 2, had a lower p H optimum, was rapidly inactivated by trypsin even in the presence of bile acid, and was moderately inhibited by added fatty acid. Like duodenal lipase(s), gastric lipase had greater activity against short chain than long chain triglycerides and was more active against the fatty acids in the 1 than in the 2 position of triglyceride. It had a much smaller apparent molecular weight (40,000 to 50,000) than duodenal lipase (>500,000) by gel filtration chromatography and had only moderate esterifying properties compared with duodenal lipase(s). Synthetic triglycerides were cleaved more slowly by gastric lipase than by pancreatic lipase in pancreatic fistula juice or duodenal content. Triglycerides of human milk particles were cleaved by gastric lipase and lipases present in duodenal content, but not by pancreatic fistula juice which lacked bile acid, suggesting that milk particle triglyceride is resistant to pancreatic lipase unless bile is present. In healthy adults, the concentration of gastric lipase in gastric contents was much less than that of pancreatic lipase in duodenal contents, and gastric lipase did not contribute significantly to the lipolytic activity of duodenal content after a test meal. Gastric lipase was significantly decreased in the gastric contents of 3 achlorhydric patients. Medium chain triglyceride was not cleaved by 16 hr of incubation at p H 1.8 or 1 hr of incubation at p H 1, suggesting that acid does not occur. Gastric lipase probably contributes to digestion of milk triglyceride in infants, as well as to hydrolysis of administered medium chain triglyceride, especially in children with decreased pancreatic lipase concentrations. Its limited activity against long chain triglyceride suggests that gastric lipase has little role in normal fat digestion in adults.