Summarylipid in an acid environment (pH 3.0-6.0), could continue to actTen to 30% of dietary fat is hydrolyzed in the stomach by lingual lipase, an enzyme secreted from lingual serous glands. We investigated the substrate specificity of this enzyme as well as the potential of lingual lipase to act in the upper small intestine i.e., in the presence of bile salts and lecithin. The data presented show that partially purified preparations of rat lingual lipase and the lipase in gastric aspirates of newborn infants have identical substrate specificity: medium-chain triglycerides were hydrolyzed at rates 5-%fold higher than long-chain triglycerides; the rat and human enzymes do not hydrolyze the ester bond of lecithin or cholesteryl-ester. In contrast to pancreatic lipase, the hydrolysis of triglycerides by lingual lipase is not inhibited by lecithin. But, similar to pancreatic lipase the activity of lingual lipase is inhibited by bile salts, the extent of inhibition varying with its nature and concentration. This inactivation is not prevented by colipase but is partially averted by lipids and protein, suggesting that lingual lipase can remain active in the duodenum. The pH optimum of the enzyme (2.2-6.5 in the rat and 3.5-6.0 in human gastric aspirates) is compatible with continued activity in the .upper small intestine, especially during the neonatal period, when the luminal pH is under 6.5. The marked variation in lipase activity levels in gastric aspirates of newborn infants is probably due to individual variations in enzyme amounts. The characteristics of the lipase are however identical in infants with low, intermediate or high activity levels. Our results indicate that hydrolysis of dietary fat by lingual lipase may not be limited to the stomach but may continue in the upper small intestine. Abbreviations CMC, critical micellar concentration FFA, free fatty acid Up to one-third of dietary fat is hydrolyzed in the stomach by lingual lipase (2 1,27,28) an enzyme secreted from lingual serous glands (23,27). Fat digestion in the stomach produces mainly partial glycerides and FFA, amphiphilic substances that help disperse the fat in the stomach and intestine (56). The gastric digestion of fat greatly enhances further hydrolysis of fat by pancreatic lipase in the small intestine (6,45). Initial lipolysis in the stomach, a necessary step for normal fat absorption (45, 5 l), becomes a much more important process in conditions of physiologic or pathologic pancreatic insufficiency, such as prematurity (22,37,6 1,63) or cystic fibrosis (I 3, 39). Recent studies show that the duodenal pH is significantly lower than normal in pancreatic insufficiency (14, 15) because of impaired bicarbonate secretion (20). In these cases lingual lipase, which hydrolyzes in the upper small intestine (1 3).This study investigated the activity of lingual lipase under the conditions prevailing in the stomach and upper small intestine. The questions that we asked were the following: Does lingual lipase hydrolyze other dietary lipids such as leci...

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The extent of gastric lipolysis, fat absorption, and infant weight gain was studied in 12 preterm infants (gestational age 28.75 ± 0.50 weeks, postnatal age 6.08 ± 0.81 weeks) fed medium-chain triglyceride or long-chain triglyceride formula for 1 week in a crossover design. The former formula contained 42% of 8:0 and 10:0 and 19% of 12:0, 14:0, and 16:0; the latter formula contained only 7% of 8:0 and 10:0 and 46% of 12:0, 14:0, and 16:0. Gastric aspirates were obtained on the second and third day of formula feeding for quantitation of lipase activity and of the extent of gastric lipolysis. Fat balance studies were conducted during the last three days of each feeding regimen. The study showed that (1) there was marked hydrolysis of formula fat in the stomach during feeding of either medium-chain triglyceride formula or long-chain triglyceride formula (20% and 16%, respectively); (2) lipase activity in the gastric aspirates was less during feeding of medium-chain triglyceride formula than before the meal, which suggested stimulation of lipase secretion by long-chain fatty acid released from long-chain triglyceride formula fat or more rapid binding of lipase to ingested lipid in the medium-chain triglyceride formula; (3) fatty acid distribution in glycerides and free fatty acids showed preferential release of medium-chain (8:0, 10:0) and long-chain unsaturated (18:1, 18:2) fatty acids in the stomach. The low content of 8:0 and 10:0 in gastric triglyceride and free fatty acids suggested that medium-chain fatty acids were absorbed directly in the stomach. (4) fat balance studies showed almost identical absorption rates (84.6% ± 3.1% and 82.8% ± 4.0%) and weight gain (23.0 ± 1.5 g/d and 20.8 ± 1.8 g/d) during feeding of either medium-chain triglyceride or long-chain triglyceride formula. In this study, in which each infant was fed either formula alternately, it was shown that although the extent of fat digestion varied among infants, medium-chain and long-chain triglyceride were absorbed to the same extent by most infants.

The lingual lipase in gastric aspirates from premature infants was found to be partially stereospecific forsn‐3 esters of synthetic enantiometric triacylglycerols containing 18∶1 and 16∶0. Thesn‐3 ester was hydrolyzed about 4 times faster than the acid at thesn‐1 position with no difference in rates between 18∶1 and 16∶0. Thesn‐2 was also hydrolyzed to some extent.