title: Evidence against the temperature-dependent interconversion of histamine H1- and H2-receptors in the guinea-pig ileum.
abstract: 1 The possible temperature-dependent interconversion of histamine H1- and H2-receptors in the guinea-pig ileum suggested from previous studies was re-investigated by use of new and selective H2-receptor agonists and antagonists. 2 Chlorpheniramine, and H1-blocker, caused a rightward shift of the cumulative histamine dose-response curve at both 37 degrees C and 12 degrees C. Conversely cimetidine and tiotidine, two H2-receptor blockers, were ineffective at both temperatures. Metiamide behaved as a non competitive antagonist at 12 degrees C but only in very high concentrations. 3 Dimaprit and impromidine, two selective H2-receptor agonists, were inactive at both 37 degrees C and 12 degrees C when given alone, whereas at both temperatures they elicited the already described relaxation of the contractions induced by histamine. 4 Similar results were obtained on the guinea-pig whole ileum and on the longitudinal muscle strip: this indicates a lack of interference of the circular smooth muscle. 5 Our results allow us to conclude that no temperature-dependent interconversion of histamine H1- and H2-receptors occurs in the guinea-pig ileum.
mesh_terms: D000818:Animals; D005260:Female; D006168:Guinea Pigs; D006632:Histamine / Q000494:pharmacology; D006634:Histamine H1 Antagonists / Q000494:pharmacology; D006635:Histamine H2 Antagonists / Q000494:pharmacology; D007082:Ileum / Q000378:metabolism; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D009130:Muscle, Smooth / Q000378:metabolism*; D011968:Receptors, Histamine / Q000502:physiology*; D011969:Receptors, Histamine H1 / Q000502:physiology*; D011970:Receptors, Histamine H2 / Q000502:physiology*; D013696:Temperature
chemical_list: D006634:Histamine H1 Antagonists; D006635:Histamine H2 Antagonists; D011968:Receptors, Histamine; D011969:Receptors, Histamine H1; D011970:Receptors, Histamine H2; D006632:Histamine