Zinc-65 secretion by the exocrine pancreas of chicks fed soybean meal

Zinc 65 is a useful tool to investigate the cellular regulation of Zn-containing enzymes. Zinc is a constituent of many enzymes or enzyme systems, among which are the carboxypeptidases, carbonic anhydrases, alkaline phosphatase and glutamic dehydrogenase (1). The form of administered Zn influences absorption and secretion of the element in the body (2). It is reported that 65ZnCl2 is slowly excreted by the intestines, whereas 65Zn-EDTA is rapidly excreted. Injected 65Zn is usually taken up by both the acinar and the islet cells of the pancreas. However, the turnover is higher in the acinar cells (3). A soybean meal diet fed to baby pigs with cannulated pancreatic ducts elicited a greater pancreatic secretion than when skim milk protein was fed. Feeding soybean meal diet resulted in secreting five times as much amylase, protease and lipase and twice the volume of pancreatic juice secreted by similar pigs fed a milk diet. This phenomenon of increased secretion was attributed to conceivable traces of the soybean trypsin inhibitor activity, which remained intact in the soybean meal diet used (4, 5). Pekas, Thompson and Hays (5) did report that a correlation existed between the 65Zn activity in pancreatic juice and the total protein secreted. The present study was undertaken to investigate the cellular regulation of Zn enzyme synthesis in the pancreas and to determine whether or not inhibitors or other components in soybean meal have an effect on the rate of synthesis and release of pancreatic enzymes, particularly the carboxypeptidases, using the incorporation and depletion of 65Zn as an index. Experimental Procedure. Chicks were fed diets containing unheated or autoclaved soybean meal for 4 wk, at which time they were fasted for 8 hr. Composition of the experimental diet was essentially that used by Salman (6).