GASTRIN-RELEASING PEPTIDE STIMULATES GALLBLADDER MOTILITY BUT NOT SPHINCTER OF ODDI MOTILITY IN AUSTRALIAN BRUSH-TAILED POSSUM

The neural distribution and action of gastrin-releasing peptide in the extrahepatic biliary tree of the Australian brush-tailed possum was i nvestigated. Immunohistochemical staining of fixed specimens demonstra ted gastrin-releasing peptide-containing nerves throughout the neural plexuses of the gallbladder, sphincter of Oddi, and mucosa of the comm on bile duct. Gastrin-releasing peptide (5-2000 ng/kg) increased gallb ladder tone to a level equivalent to that produced by cholecystokinin octapeptide (160 ng/kg). This action was tetrodotoxin-insensitive. Sph incter of Oddi motility and transsphincteric flow were not altered. Po ssible mediation of the gallbladder response by gastrin was examined. Gastrin (50-2500 ng/kg) stimulated gastric acid secretion, elevated ga llbladder motility to 64% of that produced by gastrin-releasing peptid e, and did not alter sphincter of Oddi motility. In conclusion, gastri n-releasing peptide-containing nerves are found in the neural plexus o f the possum extrahepatic biliary tree. Gastrin-releasing peptide indu ces gallbladder contraction in part by a direct action on gallbladder smooth muscle and also via release of gastrin.