UROGUANYLIN IS EXPRESSED BY ENTEROCHROMAFFIN CELLS IN THE RAT GASTROINTESTINAL-TRACT

Background & Aims: Guanylin and uroguanylin are recently discovered in testinal peptides. identifying the type of cell that synthesizes and s ecretes each peptide is an important step toward defining their physio logical functions. However, the site of uroguanylin expression has not been identified, and the site of guanylin expression remains controve rsial (some studies implicate goblet cells, whereas others implicate e nterochromaffin cells). The aim of the present study was to identify c ellular sites of uroguanylin expression in the rat gastrointestinal tr act and resolve the guanylin localization controversy. Methods: Polycl onal antibodies against two independent regions of the uroguanylin pro hormone were raised and used to evaluate prouroguanylin expression by Western blotting and immunohistochemistry. In parallel, uroguanylin mR NA was localized by in situ hybridization. Results: Uroguanylin propep tide expression is high in proximal small intestine, low in stomach an d distal small intestine, and almost undetectable in large intestine. Uroguanylin-expressing eel Is are identified as a subpopulation of ent erochromaffin cells. Conclusions: Previous results showing guanylin ex pression in enterochromaffin cells appear to be a consequence of antib ody cross-reactivity for epitopes conserved between proguanylin and pr ouroguanylin. Expression of uroguanylin in enterochromaffin cells is c onsistent with the hypothesis that uroguanylin is secreted both apical ly (into the lumen) and basolaterally (into the circulation).