Inhibition of the stimulated canine exocrine pancreas by amino acids and fat

R. S. Stubbs and B. E. Stabile
Department of Surgery, Clinical School of Medicine, Wellington, New Zealand.

To investigate the possible exocrine pancreatic inhibitory actions of amino acids and fat, pancreatic fistula outputs and plasma concentrations of glucagon, somatostatin, and pancreatic polypeptide were measured for response to intravenous (IV) and intraduodenal nutrient administration in six dogs submaximally stimulated with cholecystokinin. Intravenous amino acids caused abrupt and significant 45% to 73% reductions in stimulated pancreatic protein, bicarbonate, and volume outputs. There were no significant associated changes in plasma hormone concentrations and no similar immediate pancreatic inhibition with IV mannitol, thus suggesting a possible direct inhibitory effect of amino acids. Intraduodenal amino acids and IV fat evoked no significant pancreatic output suppression. Intraduodenal fat rapidly caused a significant 40% to 62% reductions in stimulated outputs that were associated with an 81% rise in plasma pancreatic polypeptide concentration, suggesting a gut-mediated inhibition. We conclude that IV amino acids and intraduodenal fat both inhibited stimulated pancreatic secretion but probably by different mechanisms.