DETECTION OF GUANYLATE CYCLASE-A AND CYCLASE-B STIMULATED BY NATRIURETIC PEPTIDES IN GASTROINTESTINAL-TRACT OF RAT

The ultracytochemical localization of membrane-bound guanylate cyclase s A and B has been studied after stimulation with atrial natriuretic p eptide, C-type natriuretic peptide and brain natriuretic peptide in th e gastrointestinal tract of rat. The two isoforms are stimulated diffe rently by the three peptides. The results showed that the atrial and C -type natriuretic peptides stimulated guanylate cyclase activity, wher eas the brain peptide seemed not to activate enough of the enzyme to d etect. The guanylate cyclase activity had a wider distribution in stom ach and small intestine than in large intestine; nevertheless, the rea ction product of guanylate cyclase A activity had a wider localization in the stomach, whereas the reaction product of guanylate cyclase B a ctivity had a wider distribution in the small intestine. In the small and large intestine, we detected mostly similar localizations of guany late cyclase activity irrespective of the peptide used; in the stomach the reaction products of guanylate cyclase A and B were detected in d ifferent cell types or in different sites of the same cell. In all the gastrointestinal tract, guanylate cyclase activity was detected mainl y in three types of cells: exocrine and endocrine cells; undifferentia ted and mature epithelial cells; and smooth muscle cells, These locali zations of guanylate cyclase activity suggest its role in regulating g landular secretion, cellular proliferation and muscular activity.