Fat digestion in rat: role of lingual lipase.

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Abstract
Lingual lipase, an enzyme secreted by the serous glands of rat tongue, initiates the hydrolysis of dietary fat in the stomach. The effect of ligation of the esophagus (i.e., absence of lingual lipase) on triglyceride hydrolysis in the stomach and intestine was studied in adult male Sprague-Dawley rats. One h after feeding, 18.7 .+-. 3.2% of dietary triglyceride was hydrolyzed in the stomach in control animals vs. 8.6 .+-. 2.05% in the experimental group. In vitro incubation (1 h) of the stomach contents obtained 1 h after feeding led to further hydrolysis of triglyceride: 31.0 .+-. 2.9% and 15.4 .+-. 3.7% in control and esophageal ligated rats, respectively. Exclusion of saliva from the stomach led to a marked decrease in fat hydrolysis in the duodenum and ileum: the free fatty acid (FFA) level in the duodenum decreased from 55.2 .+-. 7.4% to 19.0 .+-. 2.9%; in the jejunum and ileum, FFA amounted to 77.3 .+-. 3.6% of total fatty acids in controls compared to 54.3 .+-. 7.0% after esophageal ligation. Preincubation with lingual lipase markedly facilitates the hydrolysis of milk fat by pancreatic lipase. Intragastric lipolysis is probably of major importance in physiological and pathological conditions that are associated with low pancreatic lipase levels such as prematurity or congenital absence of pancreatic lipase.