Abstract
The properties of the β1- and β2-adrenoceptor partial agonist (±)-carteolol were investigated against the β2- and β3-adrenoceptors of the taenia caecum of the guinea pig. (−)-Isoprenaline and (±)-carteolol induced concentration-dependent relaxation in this tissue. The non-selective β1- and β2-adrenoceptor antagonist (±)-propranolol (10-100 nM), the selective β2-adrenoceptor antagonist ICI 118, 551 (10-100 nM) and the non-selective β1, - β2- and β3-adrenoceptor antagonist (±)-bupranolol (10-100n M), caused a concentration-dependent rightward shift of the concentration-response curves for (−)-isoprenaline and (±)-carteolol. Schild regression plot analyses carried out for (±)-propranolol against (−)-isoprenaline and (±)-carteolol gave pA2 values of 8.35 and 8.24, respectively. Schild plot analyses of ICI 118, 551 against (−)-isoprenaline and (±)-carteolol gave pA2 values of 8.47 and 8.41, respectively Schild plot analyses of (±)-bupranolol against (−)-isoprenaline and (±)-carteolol gave pA2 values of 8.47 and 8.53, respectively. Slopes of the Schild plots were not significantly different from unity. These results suggest that the relaxant effects of (±)-carteolol in the guinea pig taenia caecum are mediated by β2-adrenoceptors but not by β3-adrenoceptors.
