title: Modification of airway histamine-receptor function with methylprednisolone succinate.
abstract: The purpose of the present study was to investigate whether glucocorticosteroids alter airway histamine-receptor function. We measured pulmonary resistance in six conscious sheep before and after inhalation challenge with 100 breaths of 5% histamine solution, without and with intravenous pretreatment with the specific H1- and H2-receptor antagonists. Inhalation of histamine (combined H1 and H2 stimulation) increased mean pulmonary resistance (RL) to 290% of baseline (p less than 0.05). Pretreatment with the H2 antagonist, metiamide (selective H1 stimulation), enhanced the effect of histamine, with a mean RL increase to 760% of baseline (p less than 0.05). Histamine challenge after pretreatment with the H1 antagonist, chlorpheniramine (selective H2 stimulation), decreased RL to 40% of chlorpheniramine value (p less than 0.05). A single intravenous bolus injection of methylprednisolone succinate (30 mg/kg) 30 min before histamine challenge suppressed the airway responsiveness to histamine, with a mean RL increase to only 186% of baseline. After methylprednisolone, selective H1-receptor stimulation with histamine elicited a blunted H1-receptor response; mean RL increased to only 248% of baseline. Both changes were significantly lower than that with histamine alone (p less than 0.05). Methylprednisolone per se blunted the chlorpheniramine-induced increase in RL which made it difficult to evaluate H2-receptor function (RL decreased to 67% of postchlorpheniramine value). However, in the presence of increased airway tone with carbachol, selective H2 stimulation with histamine decreased RL to 26% of postcarbachol value (p less than 0.05), thus excluding suppression of H2 receptors. Methylprednisolone had no effect on carbachol-induced increase in RL. In conscious sheep, methylprednisolone blunts airway responsiveness to histamine by suppressing H1 receptors without significantly altering H2 receptors or cholinergic-receptor function.
mesh_terms: D000818:Animals; D002744:Chlorpheniramine / Q000494:pharmacology; D005260:Female; D006632:Histamine / Q000494:pharmacology; D008168:Lung / Q000502:physiology; D008775:Methylprednisolone / Q000031:analogs & derivatives*; D008776:Methylprednisolone Hemisuccinate / Q000494:pharmacology*; D011968:Receptors, Histamine / Q000187:drug effects* / Q000502:physiology; D011969:Receptors, Histamine H1 / Q000187:drug effects / Q000502:physiology; D011970:Receptors, Histamine H2 / Q000187:drug effects / Q000502:physiology; D012143:Respiratory Physiological Phenomena; D012137:Respiratory System / Q000187:drug effects; D012756:Sheep
chemical_list: D011968:Receptors, Histamine; D011969:Receptors, Histamine H1; D011970:Receptors, Histamine H2; D002744:Chlorpheniramine; D008776:Methylprednisolone Hemisuccinate; D006632:Histamine; D008775:Methylprednisolone