Effect of some new Histamine H2-receptor antagonists on the guinea-pig papillary muscle.

Several histamine H2-receptor antagonists (cimetidine, ranitidine, oxmetadine and tiotidine) were tested for their activity on the papillary muscle of the guinea pig stimulated by histamine. All of the compounds exerted a competitive antagonism against histamine the order of potency being tiotidine greater than oxmetidine greater than ranitidine greater than cimetidine. Oxmetidine was the only drug which at high concentrations (10-6 M) decreased in maximum response of histamine probably because of non specific effects of the molecule already described in the literature. As it was expected, the H1-receptor antagonist, mepyramine, exerted a non-competitive antagonism.