Characterization of postjunctional alpha-adrenoceptors in the isolated aorta of the snake Bothrops jararaca

ABSTRACT

To characterize the alpha-adrenoceptors present in Bothrops jararaca aorta, selective alpha-adrenoceptor agonists and antagonists were used. The relative order of potency of the tested agonists was noradrenaline > phenylephrine > clonidine. Prazosin was more potent than phentolamine and yohimbine in antagonizing noradrenaline response, since the PA2 values were 9.91, 7.59 and 7.33, respectively. Yohimbine was also able to block the contraction produced by phenylephrine, an alpha-1 agonist. These results suggest the existence of an alpha-1 subtype of adrenoceptor in this preparation which, however, presents some different characteristics from those described for mammals.