α1 and α2-adrenoceptor-mediated pressor and chronotropic effects in the rat and rabbit

摘要: In pithed rats or rabbits the pressor effects of catecholamines sympathetic nerve stimulation can be reduced by "selective" antagonists alpha 1- (prazosin) 2 (rauwolscine) adrenoceptors. response to low and high doses intravenous noradrenaline were due predominantly 2- 1-adrenoceptors, respectively. With frequencies vasopressor stimulation, could blocked each antagonist, suggesting either that both receptors involved unlike those activated circulating noradrenaline. higher frequencies, prazosin responses but left a residual which not eliminated rauwolscine; this indicate "non-alpha" junctional activation; rauwolscine, on its own, increase indicating blockade prejunctional alpha-mediated feedback. rats, acid-base balance was critical for activation 2-adrenoceptors. The indicated adrenaline acts through 1-adrenoceptors at pH, influence increased as pH falls. Also, fell, phenylephrine xylazine decreased, respectively, mechanism change lies subsequent stage in excitation-contraction coupling. These results are discussed relation current hypotheses heterogeneity postjunctional