title: Histamine H1- and H2-receptors in the cat and their roles during alveolar hypoxia.
abstract: We sought to define the roles of H1-and H2-receptors in the cat and to evaluate the roles of these receptors during alveolar hypoxia. In pentobarbital anesthetized cats, we found that histamine infusion (1.1 microgram/kg/min for 3 min) increased cardiac output and decreased pulmonary and systemic vascular resistances. However, when cardiac output was held constant, histamine infusion induced pulmonary vasoconstriction. Histamine infusions after H1-and H2-receptor blockade (chlorpheniramine and metiamde, respctively) indicated that H2-receptors mediated systemic vasodilatation. In the lung, H1-receptors mediated vasoconstriction, and H2-receptors mediated vasodilatation. Hypoxia (10% O2) caused large increases in pulmonary vascular resistance which were not blocked by H1-, H2-, or combined H1- and H2-receptor blockade. In the intact cat, histamine does not appear to mediate hypoxic pulmonary hypertension.
mesh_terms: D000818:Animals; D002302:Cardiac Output; D002415:Cats; D002744:Chlorpheniramine / Q000494:pharmacology; D006339:Heart Rate; D006632:Histamine / Q000494:pharmacology; D000860:Hypoxia / Q000503:physiopathology*; D008168:Lung / Q000098:blood supply*; D008785:Metiamide / Q000494:pharmacology; D011650:Pulmonary Alveoli; D011968:Receptors, Histamine / Q000502:physiology*; D011969:Receptors, Histamine H1 / Q000502:physiology*; D011970:Receptors, Histamine H2 / Q000502:physiology*; D014655:Vascular Resistance; D014666:Vasomotor System / Q000502:physiology*
chemical_list: D011968:Receptors, Histamine; D011969:Receptors, Histamine H1; D011970:Receptors, Histamine H2; D008785:Metiamide; D002744:Chlorpheniramine; D006632:Histamine