Pharyngeal lipase and digestion of dietary triglyceride in man

Abstract

Lipolytic activity was studied in esophageal and gastric aspirates obtained with a nasogastric tube from 14 healthy adult subjects. Samples were collected from esophagus, first at 30-35 cm and then at 40-45 cm from the nose, as the subject, after drinking 15-30 ml of a cream-milk mixture, swallowed small amounts of water. The samples from stomach were taken last and usually contained a small amount of cream-milk mixture. Lipolytic activity was assayed using chylomicron, milk, and corn oil triglyceride as substrate. Esophageal and gastric samples both contained lipolytic activity which hydrolyzed long-chain triglyceride to diglyceride, monoglyceride, and FFTA, had a pH optimum of 5.4, and was not affected by either had a pH optimum of 5.4, and was not affected by either 0.5 M NaCl or 4 mM sodium taurodexycholate. The activity, expressed as nanomoles of chylomicron triglyceride hydrolyzed per milliter per minute, ranged from 0 to 145 in upper esophageal, 5 to 303 in lower esophageal, and 50 to 357 in gastric samples. Only a trace of lipolytic activity was found at pH 5.4 in saliva collected from the parotid, submandibular, and sublingual glands, thus excluding those tissues as a source of the activity found in esophageal and gastric aspirates. The findings suggest that in man glands in or near the pharynx secrete a lipase that acts in the stomach to hydrolyze long-chain triglyceride to partial glycerides and FFA. It is proposed this reaction is the first step in the digestion of dietary fat and that the amphiphilic lipids formed by lipolysis facilitate the emulsification of triglyceride in the stomach.