Cyclic AMP-independent relaxation mediated by beta3-adrenoceptors on guinea pig gastrointestine.

In this study, we investigated the signal transduction pathway involved in beta(3)-adrenoceptor-mediated relaxations of guinea pig gastric fundus and duodenum. In the presence of beta1- and beta2-adrenoceptor blockade, the potency (pD2 value) of catecholamines ((-)-isoprenaline, (-)-noradrenaline and (-)-adrenaline) and beta(3)-adrenoceptor agonists ((R*, R*)-(+/-)-4-[2-[(2-(3-chlorophenyl)-2-hydroxyethyl)amino]propyl]phenoxyacetic acid sodium (BRL37344) and (+/-)-[4-[3-[(1,1-dimethylethyl)amino]-2-hydroxypropoxy]-1,3-dihydro-2H-benzimidazol-2-one] hydrochloride ((+/-)-CGP12177A)) to induce relaxation was not affected by the adenylate cyclase inhibitor, 9-(tetrahydro-2-furanyl)-9H-purin-6-amine (SQ-22,536, 100 microM). Catecholamines induced an elevation of cyclic AMP and SQ-22,536 significantly abolished the responses of gastric fundus. However, cyclic AMP levels were unaltered by the beta3-adrenoceptor agonists in gastric fundus and by the five agonists in duodenum. Furthermore, the relaxant responses to catecholamines and to beta3-adrenoceptor agonists were unaffected by the cyclic AMP-dependent protein kinase inhibitor, N-(2-[p-bromocinnamylamino]ethyl)-5-isoquinolinesulfonamide (H-89, 10 microM) in gastric fundus. These results suggest that beta3-adrenoceptor-induced relaxation is mediated through both cyclic AMP-dependent and cyclic AMP-independent pathways in gastric fundus and through a cyclic AMP-independent pathway in duodenum.