title: Evidence for both H and H2-histamine receptors in rabbit atria.
abstract: Spontaneously beating isolated atria of rabbits responded to histamine (0.5-16 micrograms/ml) with positive chrono- and inotropism. However, the inotropic response was greater than chronotropic one. The concentration-response curve of histamine for chronotropic effect was markedly shifted to the right in the presence of 0.5 micrograms/ml metiamide (H2-receptor antagonist), which per se augmented the control contractile amplitude in all the experiments. The rightward shift of chronotropic concentration response curve with mepyramine (H1-antagonist) was, however, moderate. On the contrary, the inotropic concentration response curve of histamine was shifted to much greater extent to right with mepyramine (0.62 micrograms/ml) than with metiamide, thus suggesting a greater share of H1 than H2-receptors in the mediation of positive inotropic effect of histamine. The chronotropic effect appears to be mediated predominently by H2-receptors. Unlike metiamide, mepyramine did not alter the spontaneous frequency or amplitude of contraction. The present study, thus lends support for dual histamine receptors in rabbit atria.
mesh_terms: D000818:Animals; D004347:Drug Interactions; D005260:Female; D006321:Heart / Q000187:drug effects*; D006339:Heart Rate / Q000187:drug effects; D006632:Histamine / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D008785:Metiamide / Q000494:pharmacology; D009200:Myocardial Contraction / Q000187:drug effects; D011738:Pyrilamine / Q000494:pharmacology; D011817:Rabbits; D011968:Receptors, Histamine / Q000187:drug effects*; D011969:Receptors, Histamine H1 / Q000187:drug effects*; D011970:Receptors, Histamine H2 / Q000187:drug effects*; D013268:Stimulation, Chemical
chemical_list: D011968:Receptors, Histamine; D011969:Receptors, Histamine H1; D011970:Receptors, Histamine H2; D008785:Metiamide; D006632:Histamine; D011738:Pyrilamine