SIGNAL-TRANSDUCTION PATHWAY INVOLVED IN BETA(3)-ADRENOCEPTOR-MEDIATEDRELAXATION IN GUINEA-PIG TAENIA CECUM

Experiments were carried out to examine the components of the intracel lular second messenger system that is involved in beta(3)-adrenoceptor (atypical beta-adrenoceptors)-mediated relaxation in the guinea pig t aenia caecum. Propranolol and butoxamine caused competitive antagonism of the relaxant response to isoprenaline. However, propranolol or but oxamine did not significantly affect the relaxant responses to CGP 121 77 ydroxypropoxy]-1,3-dihydro-2H-benzimidazol-2-one), a beta(3)-adreno ceptor agonist. The concentration-response curves of the isoprenaline- induced increase in adenosine 3',5'-cyclic monophosphate (cyclic AMP) levels were shifted to the right in a parallel manner by propranolol a nd butoxamine. However, propranolol or butoxamine did not significantl y affect the concentration-response curve for the CGP 12177-induced in crease in cyclic AMP levels. MDL 12330 (2-phenylcyclopentyl)-azacyclot ridec-1-en-2-amine) inhibited the isoprenaline- or CGP 12177-induced i ncrease in cyclic AMP levels. These results suggest that the productio n of cyclic AMP contributes to the beta(3)-adrenoceptor (or atypical b eta-adrenoceptor)-mediated relaxation of the guinea pig taenia caecum.