title: Selectivity of 4-methylhistamine at H1- and H2-receptors in the guinea-pig isolated ileum.
abstract: The selectivity of 4-methylhistamine (4-MH) as an agonist at histamine H1- and H2-receptors has been evaluated in the guinea-pig isolated ileum. The EC50 values of 4-MH on H1- and H2-receptors that mediate contractile responses were determined. The EC50 at H1-receptors was estimated after selective blockade of H2-receptors by tiotidine and the EC50 at H2-receptors estimated after selective blockade of H1-receptors by mepyramine. The -log EC50 values at H1- and at H2-receptors were 4.57 and 5.23, respectively. The dissociation constants for the interaction of 4-MH with H1- and H2-receptors were determined. The -log KD values at H1- and H2-receptors were 3.55 and 4.27, respectively. These results suggest that 4-MH is only about 5 times as potent at H2- as it is at H1-receptors in the guinea-pig ileum and that 4-MH should be used with caution to discriminate between H1- and H2-receptors.
mesh_terms: D000818:Animals; D003983:Dibenzylchlorethamine / Q000494:pharmacology; D017259:Dimaprit; D004347:Drug Interactions; D005260:Female; D006168:Guinea Pigs; D007082:Ileum / Q000187:drug effects; D066298:In Vitro Techniques; D008297:Male; D008761:Methylhistamines / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects*; D011968:Receptors, Histamine / Q000187:drug effects*; D011969:Receptors, Histamine H1 / Q000187:drug effects*; D011970:Receptors, Histamine H2 / Q000187:drug effects*; D013890:Thiourea / Q000494:pharmacology
chemical_list: D008761:Methylhistamines; D011968:Receptors, Histamine; D011969:Receptors, Histamine H1; D011970:Receptors, Histamine H2; D003983:Dibenzylchlorethamine; C025566:4-methylhistamine; D013890:Thiourea; D017259:Dimaprit