metiamide and Hypersensitivity

Topics: Burimamide; Chemical Phenomena; Chemistry; Cimetidine; Duodenal Ulcer; Esophagitis, Peptic; Gastric Acid; Gastrins; Gastrointestinal Hemorrhage; Histamine; Histamine H1 Antagonists; Histamine H2 Antagonists; Humans; Hypersensitivity; Intrinsic Factor; Kinetics; Malabsorption Syndromes; Metiamide; Pancreas; Pepsin A; Ranitidine; Receptors, Histamine H2; Stomach Ulcer; Stress, Psychological; Zollinger-Ellison Syndrome

Ascaris suum antigen effects on mean airflow resistance (RL) and bronchial arterial blood flow (Qbr) were studied in allergic anesthetized sheep with documented airway responses. Qbr was measured with electromagnetic flow probes, and supplemental O2 prevented antigen-induced hypoxemia. Aerosol challenge with this specific antigen increased RL and Qbr significantly. Cromolyn sodium aerosol pretreatment prevented antigen-induced increases in RL but not in Qbr. Intravenous cromolyn, however, prevented increases in Qbr and RL, suggesting a role for mast cell degranulation in both bronchomotor and bronchovascular responses to antigen. Antigen-induced increases in Qbr were not solely attributable to histamine release. Indomethacin pretreatment attenuated the antigen-induced increase in Qbr, thus suggesting that vasodilator cyclooxygenase products contribute to the vascular response. Antigen challenge significantly decreased Qbr after indomethacin and metiamide pretreatment, which suggests that vasoconstrictor substances released after antigen exposure also modulate Qbr; however, released vasodilators overshadow vasoconstrictor effects. Thus antigen challenge affects Qbr by locally releasing histamine and vasodilator prostaglandins as well as vasoconstrictor substances. These effects were independent of antigen-induced changes in systemic and pulmonary hemodynamics.

Topics: Airway Resistance; Animals; Ascaris; Bronchi; Cromolyn Sodium; Female; Hemodynamics; Hypersensitivity; Indomethacin; Metiamide; Regional Blood Flow; Sheep

We have previously demonstrated a depression of airway H2-receptor function in sheep allergic to Ascaris suum antigen. To investigate whether this is a generalized defect, we studied the H1- and H2- histamine receptor functions in the pulmonary and systemic circulations of allergic and nonallergic sheep. Pulmonary arterial pressure, and cardiac output were measured for calculation of pulmonary vascular resistance (PVR) and systemic vascular resistance (SVR) before and immediately after a rapid intrapulmonary infusion of histamine (10 micrograms/kg), with and without pretreatment with H1- (chlorpheniramine) and H2- (metiamide) antagonists. Histamine alone increased mean PVR to 435 and 401% of base line and decreased mean SVR by 51 and 54% in the nonallergic and allergic sheep, respectively (P less than 0.001). In the nonallergic sheep following pretreatment with chlorpheniramine (selective H2 stimulation) or metiamide (selective H1 stimulation), histamine decreased SVR by 18 and 36%, respectively, suggesting that approximately two-thirds of the vasodepressor response was mediated by H1-receptors and one-third by H2-receptors. Combined H1- and H2-antagonists completely blocked the histamine response. In allergic sheep the histamine-induced decrease in SVR was primarily mediated by H1-receptors, because the response was blocked by H1-antagonist, chlorpheniramine, and the H2-antagonist, metiamide, had no effect. In the pulmonary circulation selective H1-stimulation caused a similar increase in PVR in allergic (365%) and nonallergic sheep (424%), whereas selective H2-stimulation caused a significant decrease in PVR in the nonallergic group (14%) but not in the allergic group.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Blood Circulation; Blood Vessels; Chlorpheniramine; Female; Histamine; Histamine Antagonists; Hypersensitivity; Metiamide; Pulmonary Circulation; Receptors, Histamine; Receptors, Histamine H1; Receptors, Histamine H2; Receptors, Histamine H3; Sheep; Stimulation, Chemical

Topics: Animals; Antigen-Antibody Reactions; Binding, Competitive; Bucladesine; Burimamide; Calcimycin; Calcium; Cholera; Cyclic AMP; Enterotoxins; Epinephrine; Histamine; Histamine H1 Antagonists; Histamine Release; Humans; Hypersensitivity; Immunoglobulin E; Isoproterenol; Leukocytes; Mast Cells; Metiamide; Prostaglandin Antagonists; Rats