Abstract
The objective of this study was to further characterize the drug specificity for activation of atypical β-adrenoceptors. The relaxant effects of (-)-isoprenaline and (-)-noradrenaline were about 40- and 20-fold as potent as the (+)-isomers, respectively. However, the isomeric activity ratio ((+)/(-)) of isoprenaline and noradrenaline in atypical β-adrenoceptors of guinea pig gastric fundus was less than that obtained for activation of β1- and β2-adrenoceptors in the guinea pig atria and trachea, respectively. The β-adrenoceptor alkylating agent, (±)-pindobind (10μM), shifted the concentration-response curves of catecholamines ((-)-isoprenaline, (-)-noradrenaline and (-)-adrenaline) and β3-adrenoceptor agonists (BRL37344 and (±)-CGP12177A) to the right by about 3-fold, respectively. (±)-Pindobind (10μM) produced greater rightward shifts of the concentration-response curves of (-)-isoprenaline in the guinea pig atria and trachea (atria, 600-fold shift, trachea, 300-fold shift). These results suggest that pharmacological properties of atypical β-adrenoceptor differ from that obtained for β1- and β2-adrenoceptors.
