title: Effects of nitric acid on carbachol reactivity of the airways in normal and allergic sheep.
abstract: The airway effect of a 4-hr exposure (via a Plexiglas hood) to 1.6 ppm nitric acid vapor were evaluated in seven normal and seven allergic sheep, i.e., animals that have a history of reacting with bronchospasm to inhalation challenge with Ascaris suum antigen. The nitric acid vapor was generated by ultrasonic nebulization of a 2% nitric acid solution. Airway effects were assessed by measuring the change in specific pulmonary flow resistance before and after a standard inhalation challenge with 2.5% carbachol aerosol. Nitric acid exposure did not produce bronchoconstriction in either group. Pre-exposure increases in specific pulmonary flow resistance after carbachol inhalation were 68% (SD +/- 13%) and 82% (SD +/- 35%) for the normal and allergic sheep, respectively. Within 24 hr, the largest post exposure increased in specific pulmonary flow resistance for the normal and allergic sheep were 108% [SD +/- 51% (P less than .06)] and 175% [SD +/- 87% (P less than .02)], respectively. We conclude that a short-term exposure to nitric acid vapor at levels below the industrial threshold limit (2 ppm), produces airway hyperreactivity to aerosolized carbachol in allergic sheep.
mesh_terms: D000403:Airway Resistance / Q000187:drug effects*; D000818:Animals; D001985:Bronchial Provocation Tests; D001986:Bronchial Spasm / Q000139:chemically induced*; D002217:Carbachol / Q000494:pharmacology*; D004347:Drug Interactions; D009566:Nitrates / Q000494:pharmacology*; D017942:Nitric Acid; D012756:Sheep; D014835:Volatilization
chemical_list: D009566:Nitrates; D017942:Nitric Acid; D002217:Carbachol