Abstract
The purpose of the present study was to characterize the atypical β-adrenoceptors involved in relaxant responses in guinea pig gastric fundus, duodenum and ileum in functional experiments with catecholamines (isoprenaline, noradrenaline and adrenaline), β3-adrenoceptor agonists (BRL37344 and CGP12177A) and a non-selective β1-, β2- and β3-adrenoceptor antagonist bupranolol, and to obtain further evidence to clarify whether there is a tissue difference in atypical β-adrenoceptors in the guinea pig gastrointestinal tissue systems. The atypical β-adrenoceptors are present in gastric fundus, duodenum and ileum of guinea pig. In the presence of propranolol (1 μM) or atenolol (100 μM) plus butoxamine (100 μM), bupranolol caused a concentration-dependent rightward shift of the concentration-response curves for catecholamines and β3-adrenoceptor agonists. There was not a significant difference of pA2 values for bupranolol against these agonists between gastric fundus, duodenum and ileum of guinea pig. These results suggest that guinea pig gastric fundus, duodenum and ileum relaxation are mediated predominantly by an atypical β-adrenoceptor population whereas the classical β1- or/and β2-adrenoceptors play a subordinate function role and that the receptors of three tissues are pharmacological identified by functional approaches. There is not a tissue difference in atypical β-adrenoceptors in the guinea pig gastrointestinal tissue systems between stomach and ileum.
