Evidence that relaxation of hog biliary muscle is mediated by the interaction between the protein inhibitor of cyclic AMP dependent protein kinase and cholecystokinin C-terminal peptides

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 determine 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 longitudinal muscle contractility. In anesthetized possums, sphincter of Oddi motility was measured by manometry, and transsphincteric flow was measured gravimetrically.

RESULTS

Somatostatin immunoreactivity was evident in gallbladder ganglia nerve cell bodies and in nerve fibers of the common bile duct and sphincter of Oddi. Somatostatin 1-14 increased circular and longitudinal muscle contraction amplitude 3-4-fold (P < 0.05), but only the longitudinal muscle contraction amplitude was tetrodotoxin sensitive. Somatostatin 1-14 stimulated spontaneous sphincter of Oddi motility in a tetrodotoxin-insensitive manner, increasing basal pressure, contraction frequency, and amplitude 2-4-fold (P < 0.05) and reducing transsphincteric flow to 25% of control (P < 0.0001).

CONCLUSIONS

Somatostatin-like immunoreactivity is present in the extrahepatic biliary tree, and somatostatin 1-14 stimulates sphincter of Oddi smooth muscle and nerves. The major action is direct stimulation of sphincter of Oddi circular muscle, which reduces transsphincteric flow.

Full and partial relaxing CCK-C-terminal fragments in hog duodenal circular muscle

The essential active moieties in the cholecystokinin (CCK) ligand for relaxing duodenal circular muscles of pigs were investigated. The decrease in isotonic tension from the normal tone was expressed as a percentage of the relaxation obtained with Ca2+-free EGTA (2 mM) solution. Inhibition was expressed as a percentage of the relaxation induced by CCK-C-terminal tetrapeptide (CCK-4, 4.23 microM) without antagonists. Amino acid sequences from CCK-(27-28) to CCK-(27-31) increased the potency. CCK-(27-30) or CCK-(27-31) attained the same extent of relative intrinsic activity as CCK-8. The amino acid sequence from Tyr27, CCK-(27), to Trp30, CCK-(30), is another prerequisite for relaxation, in addition to the sequence of CCK-4. Newly synthesized CCK-(27-30)-R derivatives with increasingly bulky substituents (R = H, ethyl, phenyl, n-butyl and allyl) were changed from full agonists to partial agonists. Phenyl, n-butyl and allyl derivatives of CCK-(27-30)-R, in particular, had a mixed agonist and antagonist action. CCK-(27-30)-allyl antagonized competitively the CCK-4-induced relaxation (IC50 = 123 (75.9-200) microM).