To determine the influence of avian pancreatic polypeptide (APP) on avian GI motility, strain-gauge transducers were implanted on the glandular stomach, thick caudodorsal and thin caudoventral muscles of the muscular stomach, and on the duodenum (cranial tract) of five young turkeys. Implants were also made on the ileum, cecum, and colon (caudal tract) of three other turkeys. Isovolumic injections of APP at six (cranial tract preparations) or four (caudal tract preparations) levels were made via a chronic jugular catheter while recording GI contractile activity in fasted birds. Injections of 2 or 5 micrograms/kg caused no statistically significant change in motility of the cranial tract. Significant depression in contraction frequency during the first 10 min post-injection resulted from an injection of 8 micrograms/kg. Injections of 10, 20, and 30 micrograms/kg depressed motility throughout the entire 30 min post-injection period. Motility of the caudal tract usually was not significantly affected by injections of 5 and 10 micrograms/kg doses. Larger doses (20 and 30 micrograms/kg) significantly depressed caudal tract motility during the first 10 min post-injection but not throughout the 30 min post-injection period. In both cranial and caudal portions of the tract, depression of contractile activity by injections of APP persisted longer following larger doses. The highest plasma APP levels in turkeys, found at about 1 hr post-prandially, were still less than plasma levels following IV injection of 5 micrograms/kg. Since the latter injection caused no apparent alteration in Gi motility, APP may have little or no physiological role in regulation of avian GI motility.
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