Plasma secretin and pancreatic response to various stimulants including a meal

In dogs with gastric and duodenal Thomas cannulas, we investigated the threshold dose range of exogenous secretin and intraduodenal HCl for pancreatic bicarbonate secretion and, with a recently developed radioimmunoassay, measured the increase in plasma secretin concentrations. Synthetic secretin (2.5, 7.5, and 22.5 ng X kg-1 X h-1) was dissolved in saline or 0.1% dog albumin and given with or without a background infusion of 30 ng X kg-1 X h-1 of caerulein. The minimal dose of secretin that elicited a significant pancreatic bicarbonate response as well as an increase in plasma secretin concentration was 7.5 ng X kg-1 X h-1 when administered with albumin and 22.5 ng X kg-1 X h-1 without albumin. The threshold dose for duodenal HCl was 2 mmol X h-1. The threshold secretin dose for bicarbonate secretion and for an increase in plasma secretin levels was unchanged with a background caerulein infusion. Furthermore, postprandial secretin concentrations were measured. After a meat meal plasma secretin release appeared to occur in spikes up to 10 pmol X l-1 corresponding to secretin levels seen during infusion of 7.5 ng X kg-1 X h-1 of secretin and intraduodenal acid perfusion at a dose of 2 mmol X h-1.

Intraduodenal emulsions of oleic acid augment acid-induced canine pancreatic secretion

To study interactions between intraduodenal acid and emulsified oleic acid, dogs with chronic gastric and pancreatic fistulas received two sets of intestinal perfusates. The first set contained HCl plus bovine serum albumin (BSA) with or without 20 mM oleic acid. The BSA and HCl were varied so that each 50 ml contained 1, 2, or 4 meq of acid titratable from an initial pH of 2.0 or 3.5 to an end-point pH of 4.5. Oleic acid significantly enhanced pancreatic bicarbonate and protein outputs induced by acidified BSA. In additional studies, a less soluble protein solution, a 1:1 mixture of bovine hemoglobin and ovalbumin (HB-OV), was utilized. Fixed amounts of HCl (1, 2, or 4 meq/50 ml) were added to native or pepsin-digested HB-OV solution with or without 20 mM oleic acid. In these studies, initial pH and titratable acid (to end-point pH 4.5) varied with the nature of the HB-OV (undigested or digested), as well as with the amount of HCl added. Under these conditions, digested HB-OV and oleic acid potentiated acid-induced bicarbonate output, but only in those solutions with the greatest amount of added HCl. Acid-induced bicarbonate or protein outputs were not further augmented upon combination of HB-OV digests with oleic acid. We conclude that acid-induced pancreatic bicarbonate secretion is potentiated by intraduodenal protein digests and emulsified fatty acids.