Abstract 4-(2-Hydroxy-3-isopropylaminopropoxy)indole (LB46) is a competitive β-adrenoreceptor blocking drug with a potency of between 4 and 7 times that of propranolol on the guinea-pig isolated trachea and atria (chronotropic effects). LB46 itself produces tracheal relaxation which may result from an indirect sympathomimetic action. The influence of uptake into adrenergic nerves on pA2 and pA10 values for LB46 and propranolol, when using noradrenaline as agonist drug, has been assessed from results obtained on trachea in the presence and absence of cocaine (10−5m). In the absence of cocaine the slopes of the regression of log (dose ratio —1) against negative log molar concentration of antagonist were less than the theoretical value of —1·0. In the presence of cocaine the slopes of these regressions approached —1·0. Thus values of (pA2-pA10) also deviated from the theoretical value in the absence of cocaine but approached it if cocaine was present in the bath fluid.
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Moore et al. (1970) studied this question.