Effect of pancreatic polypeptide on canine migrating motor complex and plasma motilin

A potential role of pancreatic polypeptide (PP) in the regulation of phase III of the migrating motor complex (MMC) was investigated in conscious dogs before and during bilateral vagal blockade. After a control fasting period, cyclical increments in plasma PP occurred with peak levels of 45 +/- 8 pmol/l coinciding with late phase II MMC motility. By contrast, after food a substantially higher (approximately five times peak fasting concentrations) and more prolonged elevation of PP was observed, in association with a postprandial pattern of activity. To approximate fasting plasma PP concentrations, porcine PP was infused at 100 pmol X kg-1 X h-1, which produced levels of plasma PP of 99 +/- 8 pmol/l. At this dose PP had no effect on phase III activity. However, at a dose of 400 pmol X kg-1 X h-1, which achieved plasma PP concentrations (283 +/- 33 pmol/l) similar to postprandial levels, there was a specific inhibition of phase III in the lower esophageal sphincter, stomach, duodenum, and upper jejunum. The phase III-associated increment of plasma motilin was also inhibited by this dose of PP. These inhibitory effects at the 400 pmol X kg-1 X h-1 dose of PP were also observed after bilateral blockade of the vagus nerves. Our results suggest that PP has no significant role in the modulation of phase III of the fasting MMC nor does it induce a typical feeding motor pattern. The selective inhibition of both phase III and the associated rise in plasma motilin by PP plasma levels similar to postprandial concentrations does, however, point to a possible role for pancreatic polypeptide in the postprandial inhibition of phase III of the MMC.