Effect of Excess Dietary Zinc on Pancreatic Exocrine Function in the Chick

Abstract

The effects of excess dietary zinc (Zn) on exocrine pancreatic function were studied in chicks. A purified diet based on crystalline amino acids and sucrose was employed in several experiments, and a practical type of diet based on corn and soybean meal was used in one experiment for the purpose of comparison. Additions of as little as 100 mg Zn/kg as ZnO to the purified diet markedly elevated pancreatic Zn concentration, whereas liver and plasma Zn were moderately increased. Histological examination of the pancreas showed alterations in acinar structure due to Zn intoxication. The activities of the pancreatic exportable enzymes amylase, lipase, trypsinogen and chymotrypsinogen were each decreased by such levels of Zn feeding. Reductions of pancreatic enzyme activities were associated with reductions in the digestibility of dietary starch and in tissue α-tocopherol concentrations. Chicks fed the nonpurified (i.e., soy-containing) diet accumulated much less Zn in the pancreas (about one-tenth as compared with the purified diet); the addition of as much as 2000 mg Zn/kg as ZnO to this diet produced only a small increase in pancreas Zn concentration, and did not affect exportable pancreatic enzyme activities or tissue α-tocopherol concentrations. These results indicate that dietary factors that reduce Zn availability may also reduce Zn toxicity. Chicks fed the purified diet with excess Zn had slightly higher liver selenium (Se) concentrations, but this effect was not associated with changes in the activity of Se-dependent glutathione peroxidase in that organ. Nutritional deprivation of Se did not affect the extent of Zn-induced acinar damage. These studies demonstrate that the acinar pancreas is a target organ of Zn toxicity in the chick.