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

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Abstract
Several histamine H2-receptor antagonists (cimetidine, ranitidine, oxmetidine 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 > oxmetidine > ranitidine > cimetidine. Oxmetidine was the only drug which at high concentrations (10−6 M) decreased the 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.