M. H. Pubols

Exocrine function of the chick pancreas as affected by dietary soybean meal and carbohydrate.

Chicks develop an enlarged pancreas when fed unheated soybean meal. Autoclaving the meal destroys or inactivates the heat-labile component(s) which cause this effect on the pancreas 5 . Recent histological studies in our laboratory 24 have confirmed that this enlargment is due to hyperplasia of the pancreatic acinar cells, but the cause of this hyperplasia is not known 2 . Homogenates of the enlarged pancreas have lower amounts of amylase, but higher levels of trypsin and chymotrypsin 20 . Grossman et al. 9 . and more recently Desnuelle et al. 6 , suggested that differences in levels of pancreatic enzymes could be due to different rates of synthesis in response to dietary composition and/or an altered rate of secretion of enzymes from the pancreas. Most of the published results on pancreatic changes were obtained with pancreatic homogenates, a technique that precludes distinction between the suggested alternatives. The purpose of the present study was to determine the effect of changing the nature, or source, of the dietary protein and carbohydrate on the volume and composition of the exocrine pancreatic secretion of chicks. Experimental Procedure. Chicks were raised from 1 day of age to 3 weeks on four different diets containing autoclaved or unheated soybean meal with either glucose or cornstarch as the carbohydrate source. Composition of the basal diet has been described 21 . Twelve birds (3/ treatment) were used for the pancreatic function studies and 36 (9/ treatment) for the determinations of intestinal pH. Chicks were anesthetized with pentobarbital sodium (20 mg/kg, intravenously) and the main pancreatic duct (of the three or four pancreatic ducts present in the chick) was cannulated using polyethylene tubing (PE 50).

Chemical and Microscopic Nature of Pancreata from Chicks Fed Unhealed Soybean Meal

Summary When chicks were fed diets containing 25% protein, those which had been fed unheated soybean meal developed pancreata which were much larger than pancreata from chicks which had been fed heated soybean meal. Histological examination did not indicate any variance between pancreata from either of the two treatments. The DNA, RNA, and protein levels, per unit weight, were not different whether unheated or autoclaved soybean meal was the source of protein in the diets. In addition, the moisture level in pancreata from both treatments was identical. These data indicate that the pancreas enlargement caused by feeding raw soybean meal is a result of hyperplastic rather than hypertrophic changes.

Changes in Pancreatic Enzymes as a Function of Diet in the Chick.

The phenomena of enzyme induction and repression are very well established in microorganisms, yet for vertebrates and mammals these have not been thoroughly investigated. The ratio of pancreatic enzymes is variable among species( 5 , 9 , 12 , 13 ). Determinations of enzymes in homogenates of pancreata from rats fed either starch-rich or casein-rich diet show that specific activities of amylase and chymotrypsin reflect the starch and casein content of the diet( 15 ). In chicks, the pancreata enlarge when unheated soybean meal is consumed. These pancreata show depletion of zymogen granules to a greater extent than the corresponding pancreata from chicks fed autoclaved soybean meal diet. This histological evidence was confirmed by chemical analysis ( 1 ). We investigated the rate of synthesis of enzymes by the pancreas of chickens after an adaptation period of 4 weeks on either unheated or autoclaved soybean meal. Experimental. Two groups of chicks were fed either unheated or autoclaved soybean meal for 4 weeks. The composition of the basal diet was essentially that used by Dal Borgo( 4 ). After this adaptation period, the chicks were fasted: 3 birds of each group were sacrificed at 0, 6, 12, 16, and 22 hours after the start of fast. After 16 hours of fasting, each group was divided into 2 subgroups, one of which was fed the same diet as before the fast. and the other the alternate diet. Three chicks from each of the 4 subgroups were sacrificed after 2 and 6 hours on the diet. The pancreata were excised aid weighed (after removal of extraneous tissue), then stored at −15°C. Trypsin and chymotrypsin were ashayed using p-toluene-sulphonyl-L-arginine-methyl ester (TAME) and N-Benzoyl-L- tyrosine ethyl ester (BTEE), respectively ( 7 ). Amylase activity was determined by the 3,5,-(dini-trosalicylate method( 3 ). Protein in the pancrcatic homogenates was determined by measuring the absorbancy at 280 and 260 μ to correct for nucleic acids ( 10 ).