Release of avian pancreatic polypeptide by various intraluminal contents in the stomach, duodenum, or ileum of turkeys

Recent studies on regulation of gastric motility in turkeys

Recent studies have been aimed at determining how gastroduodenal contractions are initiated and at regulation of the stomach during the intestinal phase of gastric regulation. Intrinsic, myogenic, electrical slow waves, the principal regulators of motility in the mammalian gut, have not been found in the avian gut. Instead, contractions appear to be initiated by a neurogenic pacemaker located between the gastric isthmus and the pylorus. Pacemaker impulses travel over the myenteric plexus to the glandular stomach and the duodenum, and to the muscles of the muscular stomach to initiate contractions. Extrinsic innervation does not appear to be involved in this initiation. The role of two hormones, avian pancreatic polypeptide (aPP) and cholecystokinin (CCK), in regulation of gastric motility has been examined. Both hormones are released postprandially by the presence of ingesta in the upper small intestine and both depress gastroduodenal motility when administered to fowl. Thus, aPP and CCK slow gastric emptying to allow more time for intestinal digestion.

Influence of avian pancreatic polypeptide on pancreatic and biliary secretion in laying hens

White Leghorn hens, 14 to 29 wk of age, were surgically prepared with cannulae for collecting secretions from the cystic duct and the duct draining the ventral pancreatic lobe and for infusing the jugular vein with avian pancreatic polypeptide (aPP) or saline. A plasma infusion rate that produced a plasma level of 15 ng of aPP/mL was used. A comparison of values obtained during saline infusion with those obtained during aPP infusion indicated that pancreatic and biliary secretory volumes and pancreatic total protein concentration were significantly depressed by aPP. The pH of pancreatic and biliary secretions were not significantly affected by aPP. Because aPP also depresses gastric secretion and motility in hens, it is proposed that its physiological role may be to oppose or modulate the actions of other, stimulatory gastrointestinal hormones.

Influence of cholecystokinin, vasoactive intestinal peptide and secretin on plasma concentration of avian pancreatic polypeptide in laying hens

The influence of saline infusion (i.v.) followed by infusion of either cholecystokinin, vasoactive intestinal peptide, or secretin on plasma concentration of avian pancreatic polypeptide (aPP) was studied in sixteen 18-26-week old Single Comb White Leghorn hens. Three concentrations were used for each hormone. Blood was drawn after both saline and hormone infusions and assayed for aPP content. No significant influence of any of the three hormones on plasma aPP level was found in either fed or fasted hens.

The influence of avian pancreatic polypeptide on gastric secretion and motility in laying hens

The effects of pancreatic polypeptide (PP) on digestive functions have been studied extensively in mammals. The only two previous studies on the effects of PP on avian (aPP) gastrointestinal function employed bolus injections (i.v.) of the hormone, which may have resulted in nonphysiological plasma levels of aPP. The present study was to determine the effect of aPP infused (iv) at levels simulating postprandial plasma concentrations. Young laying hens were prepared with chronic proventricular and jugular cannulas and with strain gauge transducers sutured to the serosa of the gizzard. In each experiment, a control saline infusion was followed by infusion sufficient to achieve either 7.5 or 15 ng aPP/ml of plasma. Volume, pH, and pepsin content of gastric secretions and frequency and amplitude of gastric contractions were determined. At 15 ng aPP/ml of plasma, secretory volume (P less than .01) and contractile frequency (P less than .001) were significantly depressed as compared to similar data during the saline infusion. At 7.5 ng aPP/ml of plasma, only contractile frequency (P less than .01) was depressed.

Effect of truncal vagotomy on intestinal phase of pancreatic polypeptide release in dogs

In order to elucidate the role of the vagus nerve in the intestinal phase of pancreatic polypeptide (PP) release, mongrel dogs were given a 4-min intraduodenal infusion of saline, 20% glucose, or 10% soybean oil solution (50 ml each), before and one month after truncal vagotomy including pyloroplasty (TV). The saline infusion did not change the basal PP level, while the glucose infusion elicited a monophasic transient PP release, and the soybean oil infusion elicited a monophasic prolonged PP release in the intact dogs. The PP response following glucose infusion was almost abolished after TV, while the PP response to fat was attenuated, but a significant increase was nevertheless observed after TV. These results suggest that the vagus nerve has an important role in the intestinal phase of PP release and that other factors, e.g. hormonal, might also be involved in the regulatory mechanism, especially after fat loading.