Occurrence of H1- and H2-histamine receptors in the guinea-pig gall bladder in situ.

1 Histamine has a dual action on the in situ gall bladder of the guinea-pig: a spasmogenic and a relaxant effect mediated through H1- and H2-receptor stimulation respectively. 2 The contracturant action, mimicked by 2-(2-aminoethyl) thiazole (a specific H1-receptor agonist), is blocked by mepyramine and the relaxation, mimicked by dimaprit (a specific H2-receptor agonist), is inhibited by cimetidine.