Responses to histamine and selective H2-receptor agonists in lung parenchymal strips from normal and sensitized guinea-pigs
The bronchodilator activity of the H2-recptor agonist, dimaprit, was assessed in vitro and in vivo. In vitro dimaprit relaxed guinea pig tracheal spirals and parenchymal strips that were constricted by the H1 receptor agonist, 2-PEA, or by carbachol. The H2-receptor antagonist, metiamide, inhibited this effect of dimaprit in vitro on both tissues constricted by 2-PEA but not on the carbachol constricted tracheal spiral. Intravenous infusion of dimaprit in the intact guinea pig resulted in reversal of bronchoconstriction induced by subcutaneous injection of 2-PEA. In vivo pretreatment with the H2-recptor antagonist, metiamide, resulted in a diminished sensitivity to the bronchodilating effects of intravenous dimaprit.