Identification and localization of 5-HT1P receptors in the guinea pig pancreas.
Enteropancreatic 5-hydroxytryptamine (5-HT)-immunoreactive nerve fibers have recently been described. To test the hypothesis that pancreas contains 5-HT receptors similar to those that characterize the enteric nervous system, binding of 5-[3H]HT to pancreatic membranes was investigated. Membranes were prepared by differential centrifugation from guinea pig pancreas, and binding of 5-[3H]HT was measured by use of a rapid filtration assay. Alternatively, 5-[3H]HT-binding sites were analyzed and located by radioautography on frozen sections of unfixed pancreas. The 5-HT1P receptor-specific antagonist, N-acetyl-5-hydroxytryptophyl-5-hydroxytryptophan amide (5-HTP-DP), was used to define nonspecific binding in all assays. High-affinity reversible binding of 5-[3H]HT to pancreatic membranes was found. Good agreement was observed when Kd was determined from saturation isotherms (Kd = 2.1 +/- 0.4 nM; Bmax = 0.6 +/- 0.07 pmol/mg protein) or from the ratio of association and dissociation constants (2.7 +/- 0.04 nM). As is true of 5-[3H]HT binding to enteric 5-HT1P receptors, binding of 5-[3H]HT to pancreatic membranes was inhibited by 5-HTP-DP, 5- and 6-hydroxyindalpine (agonists at 5-HT1P receptors), and guanine nucleotides. In contrast, binding of 5-[3H]HT to pancreatic membranes was not inhibited by a variety of compounds known to bind to other types of 5-HT receptor, to the neuronal 5-HT transporter, to alpha- or beta-adrenoceptors, or to dopamine receptors. We concluded that pancreas contains 5-HT1P receptors with properties similar to those of bowel. Radioautography and immunocytochemistry with an anti-idiotypic antibody that recognizes 5-HT receptors revealed that pancreatic 5-HT1P receptors (identified with appropriate inhibitors of 5-[3H]HT or antibody binding) were concentrated in ganglia, nerves, and unidentified cells in both exocrine and endocrine pancreas. These observations suggest that future studies of 5-HT's role in pancreatic physiology should concentrate on enteropancreatic innervation and 5-HT1P receptors.
Kirchgessner
A L
AL
Department of Anatomy and Cell Biology, Columbia University College of Physicians and Surgeons, New York, New York 10032.
Liu
M T
MT
Tamir
H
H
Gershon
M D
MD
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000704:Analysis of Variance; D000818:Animals; D001205:Ascorbic Acid / Q000494:pharmacology; D001345:Autoradiography; D001667:Binding, Competitive; D002462:Cell Membrane / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006168:Guinea Pigs; D007150:Immunohistochemistry; D008297:Male; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D010179:Pancreas / Q000737:chemistry* / Q000166:cytology / Q000294:innervation; D011985:Receptors, Serotonin / Q000032:analysis* / Q000187:drug effects; D012701:Serotonin / Q000378:metabolism; D014316:Tritium
D011985:Receptors, Serotonin; D014316:Tritium; D012701:Serotonin; C022571:adenosine 5'-O-(3-thiotriphosphate); D016244:Guanosine 5'-O-(3-Thiotriphosphate); D000255:Adenosine Triphosphate; D001205:Ascorbic Acid