Evidence for an intestinal mechanism of pancreatic polypeptide release

The purpose of this study was to define the existence of an intestinal phase of pancreatic polypeptide (PP) release and to assess whether it was mediated by a cholinergic-sensitive mechanism. Four conscious dogs with 20-cm upper intestinal Thiry-Vella loops and chronic gastric fistulas were used. The Thiry-Vella (T-V) loops were perfused with 10% liver extract or 0.154 M NaCl at a rate of 1 ml/min for 120 min. In a separate experiment, 240 ml of 10% liver extract was infused over a 5-min period into the stomach via the gastric fistula. Basal PP levels were 29 +/- 4 fmol/ml. The gastric infusion of liver extract caused a significant increase of plasma PP levels to a peak of 215 +/- 29 fmol/ml (P less than 0.05). The perfusion of the T-V loop with liver extract significantly increased plasma PP levels over basal to a peak of 73 +/- 14 fmol/ml (P less than 0.05). This value was significantly less than that released by gastric infusion of liver extract (P less than 0.05). Perfusion of the loop with NaCl did not significantly alter basal plasma PP levels (P greater than 0.05). PP release by perfusion of the T-V loop with liver extract was abolished by atropine intravenous bolus (0.2 mg/kg). Although the combination of bethanechol (100 microgram/kg/hr intravenous) and liver extract consistently increased the plasma levels of PP, the values did not attain statistical significance when compared to liver extract alone (P greater than 0.05). The data presented are thus consistent with the hypothesis that there is an enteric phase of pancreatic polypeptide release and that this enteropancreatic reflex is mediated by a cholinergic-sensitive mechanism which might be hormonal or neural.