Retrograde movement of digesta in the duodenum of the chick: extent, frequency, and nutritional implications

Movement of digesta from the duodenum to the gizzard of chicks was assessed by injection of 99mTc-diethyl-triamino-pentaacetic acid via an indwelling cannula in the hepatic bile duct. The change in location of isotope with time was followed with a Gamma Camera. About 40% of the injected isotope refluxed to the gizzard within 2 minutes of injection. Clearance of the isotope from the gizzard had a T1/2 of some 20 minutes. Some possible implications of retrograde movement of digesta were examined. Cholesterol, bile salts and pancreatic enzymes were found in the gizzard at 10% to 20% of duodenal concentrations. The proteolysis and lipolysis in the gizzard and duodenum were determined in chicks fed a duet containing 91Y as a non-absorbed reference substance. Thirty percent of the feed triglycerides were found hydrolysed in the gizzard as compared to 50% to 60% in the duodenum. Proteins were 30% to 50% trichloroacetic acid soluble in the gizzard reaching almost 70% in the duodenum. A small net secretion of both fatty acids and protein was observed in the gizzard, probably due to reflux of endogenous secretions from the duodenum. The nutritional significance of these results is discussed.