Abstract

Hyperosmolar challenge of airway epithelium stimulates the release of epithelium-derived relaxing factor (EpDRF), but the identity of EpDRF is not known. We examined the effects of pharmacological agents on relaxant responses of methacholine (3 × 10^-7 M)-contracted guinea pig perfused trachea to mucosal hyperosmolar challenge using d-mannitol. Responses were inhibited by gossypol (5 ×10^-6 M), an agent with diverse actions, by the carbon monoxide (CO) scavenger hemoglobin (10^-6 M), and by the heme oxygenase (HO) inhibitor zinc (II) protoporphyrin IX (10^-4 M). The HO inhibitor chromium (III) mesoporphyrin IX (10^-4 M) was not inhibitory, and the HO activator heme-l-lysinate (3 ×10^-4 M) did not evoke relaxant responses. The CO donor tricarbonyldichlororuthenium (II) dimer (2.2 ×10^-4 M) elicited small relaxation responses. Other agents without an effect on responses included: apyrase, adenosine, 6-anilino-5,8-quinolinequinone (LY83583), proadifen, (E)-3-[[[3-[2-(7-chloro-2-quinolinyl)ethenyl]phenyl][[3-(dimethylamino)-3-oxopropyl]thio]methyl]thio]-propanoic acid (MK 571), diphenhydramine, glibenclamide, HgCl₂, tetrodotoxin, nystatin, α-hemolysin, 8-bromoguanosine 3',5'-cyclic monophosphothioate, Rp-isomer, 12-O-tetradecanoylphorbol-13-acetate, cholera toxin, pertussis toxin, thapsigargin, nifedipine, Ca²⁺-free mucosal solution, hydrocortisone, and epidermal growth factor. Cytoskeleton inhibitors, includingerythro-9-(2-hydroxyl-3-nonyl)adenine, colchicine, nocodazole, latrunculin B, and cytochalasins B and D, had no effect on relaxation responses. The results suggest provisionally that a portion of EpDRF activity may be due to CO and that the release of EpDRF does not involve cytoskeletal reorganization.