Gastrin-Releasing Peptide Stimulates Gallbladder Motility but Not Sphincter of Oddi Motility in Australian Brush-Tailed Possum

The neural distribution and action ofgastrin-releasing peptide in the extrahepatic biliarytree of the Australian brush-tailed possum wasinvestigated. Immunohistochemical staining of fixedspecimens demonstrated gastrin-releasing peptide-containing nervesthroughout the neural plexuses of the gallbladder,sphincter of Oddi, and mucosa of the common bile duct.Gastrin-releasing peptide (5-2000 ng/kg) increasedgallbladder tone to a level equivalent to that produced bycholecystokinin octapeptide (160 ng/kg). This action wastetrodotoxininsensitive. Sphincter of Oddi motility andtranssphincteric flow were not altered. Possible mediation of the gallbladder response bygastrin was examined. Gastrin (50-2500 ng/kg) stimulatedgastric acid secretion, elevated gallbladder motility to64% of that produced by gastrin-releasing peptide, and did not alter sphincter of Oddi motility.In conclusion, gastrinreleasing peptide-containingnerves are found in the neural plexus of the possumextrahepatic biliary tree. Gastrin-releasing peptide induces gallbladder contraction in part by adirect action on gallbladder smooth muscle and also viarelease of gastrin.