CONTROL OF CANINE GASTRIC-EMPTYING OF FAT BY LIPOLYTIC PRODUCTS

Dietary fat is ingested in three forms: 1) in solid food, 2) as aqueou s emulsions, and 3) as unemulsified, liquid oil. On the basis of a sca nt previous literature, we postulated that liquid fat (emulsions or oi ls) would empty from the stomach at speeds that varied with the amount s ingested but that this dynamic would be modulated by feedback inhibi tion from lipolytic products. To test these ideas, we used a gamma cam era to track gastric emptying of I-123-labeled fat in dogs with chroni c pancreatic fistulas by which lipase was excluded from or replenished in the duodenum in varied amounts after dogs were fed 15-, 30-, and 6 0-g loads of liquid fat given with solid foods or as emulsions. We als o tracked concurrent gastric emptying of In-113m, which marked the sol id food phase or the water phase of emulsions. In some studies, we use d a potent and specific inhibitor (orlistat) of pancreatic and gastric lipases to assess how lipolytic products modulated emptying of liquid fat. In the absence of pancreatic enzymes, both oils and emulsions em ptied initially at high speeds that varied with fat loads, but emptyin g slowed 20 min after ingestion of emulsions and 60 min after ingestio n of unemulsified oil. Studies with orlistat indicated that these chan ges in rates resulted from liberation of gastric lipolytic products. E mptying of oil emulsions was not altered by duodenal replenishment wit h pancreatic enzymes, but emptying of unemulsified oil was inhibited i n a dose-related fashion, such that maximal inhibition was achieved wh en pancreatic enzymes were replenished at greater than or equal to 40% of normal amounts. Studies with orlistat confirmed that this dose-dep endent slowing was due specifically to lipase. Emptying of solid food was much more sensitive to replenishment with enzymes, so that a 10% r eplenishment maximally inhibited solid emptying.