SOMATOSTATIN STIMULATES THE BRUSH-TAILED POSSUM SPHINCTER OF ODDI IN-VITRO AND IN-VIVO

Background & Aims: Somatostatin, a neuropeptide and hormone, is found in the biliary tract of several species. The aim of this study was to map the distribution of somatostatin-like immunoreactive nerve fibers in the extrahepatic biliary tract of the Australian possum and to dete rmine the pharmacological effects of somatostatin 1-14 on sphincter of Oddi activity in vitro and in vivo. Methods: Tissue was harvested for immunohistochemistry and sphincter of Oddi for circular or longitudin al muscle contractility, In anesthetized possums, sphincter of Oddi mo tility was measured by manometry, and transsphincteric flow was measur ed gravimetrically. Results: Somatostatin immunoreactivity was evident in gallbladder ganglia nerve cell bodies and in nerve fibers of the c ommon bile duct and sphincter of Oddi, Somatostatin 1-14 increased cir cular and longitudinal muscle contraction amplitude 3-4-fold (P < 0.05 ), but only the longitudinal muscle contraction amplitude was tetrodot oxin sensitive, Somatostatin 1-14 stimulated spontaneous sphincter of Oddi motility in a tetrodotoxin-insensitive manner, increasing basal p ressure, contraction frequency, and amplitude 2-4-fold (P < 0.05) and reducing transsphincteric flow to 25% of control (P < 0.0001). Conclus ions: Somatostatin-like immunoreactivity is present in the extrahepati c biliary tree, and somatostatin 1-14 stimulates sphincter of Oddi smo oth muscle and nerves. The major action is direct stimulation of sphin cter of Oddi circular muscle, which reduces transsphincteric flow.