INTRACISTERNAL RAT PANCREATIC-POLYPEPTIDE STIMULATES GASTRIC-EMPTYINGIN THE RAT

Pancreatic polypeptide (PP) has been shown to alter gastrointestinal f unctions, including increased gastric acid secretion and motility foll owing brain stem injections of PP. The present study investigated the effect of an intracisternal injection of PP on the rate of gastric emp tying. Additionally, the efficacy of the rat and bovine forms of the p eptide was compared. Rats anesthetized with ether received an intracis ternal injection of rat PP, bovine PP, or vehicle and, upon regaining consciousness, were fed a liquid test ''meal.'' Intracisternal rat PP produced a marked enhancement in gastric emptying compared with contro l animals. Bovine PP, at doses equimolar to or three times greater tha n the effective rat PP dose, produced no change in gastric emptying. P retreatment with systemic atropine prior to central injection of rat P P eliminated the stimulation of emptying, suggesting that PP acts thro ugh a cholinergic mechanism. When equimolar doses of rat or bovine PP were microinjected directly into the dorsal vagal complex, the region containing PP receptors, both were capable of stimulating antral motil ity. The response to bovine PP, however, was delayed and reduced compa red with that seen following rat PP. The results suggest that rat PP s trongly stimulates gastric emptying in rats and that bovine PP, depend ing on the route of administration, is either ineffectual or a weaker agonist for central PP receptors.