title: Antagonistic activity of tiotidine and ranitidine on guinea-pig and rabbit atria.
abstract: Isolated, spontaneously beating atrial pairs from rabbits and guinea-pigs were used to determine and to compare the activity of ranitidine and tiotidine as antagonists of histamine stimulated chronotropic activity. Ranitidine produced a classical competitive, reversible antagonism of histamine effects with a pA2 in rabbit atria of 8.2. In contrast, tiotidine produced both a dextral shift of the log dose-response curve, as well as a previously unreported suppression in the maximal response produced by histamine. In accordance with receptor theory, this type of activity represents a dualistic antagonism of histamine chronotropic responses.
mesh_terms: D000818:Animals; D002927:Cimetidine / Q000031:analogs & derivatives* / Q000494:pharmacology; D005260:Female; D006168:Guinea Pigs; D006339:Heart Rate / Q000187:drug effects*; D006633:Histamine Antagonists; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects; D011817:Rabbits; D011899:Ranitidine / Q000494:pharmacology*
chemical_list: D006633:Histamine Antagonists; D002927:Cimetidine; D011899:Ranitidine; C023990:tiotidine