We tested the hypothesis that airway perfusion modifies the contractile response of airway smooth muscle to allergen challenge by influencing the clearance of locally released spasmogens. In six intact, lightly sedated, sheep allergic to Ascaris suum, we measured tracheal mucosal blood flow (Q̇tr) with a soluble gas uptake method and tracheal dead space (Vtr), an index of airway smooth muscle tone, by helium dilution before and serially after local aerosol challenge with A. suum extract or ragweed extract (control). The former challenge was repeated during continuous intravenous infusion of either vasopressin or nitroglycerin, which by themselves had no effect on Vtr and decreased and increased Q̇tr, respectively. Ragweed had no effect on Q̇tr and Vtr, whereas A. suum increased mean (± SE) Q̇tr by 111 ± 31% (p < 0.05) and decreased mean Vtr by 15 ± 2% (p < 0.05) immediately after challenge, with Q̇tr returning to baseline by 40 min and Vtr by 80 min. Vasopressin infusion prevented the A. suum-induced increase in Q̇tr and prolonged the decrease in mean Vtr (p < 0.05). During nitroglycerin infusion, A. suum failed to alter Q̇tr or Vtr. Vasopressin and nitroglycerin had no effect on the contractile responses of tracheal smooth muscle to A. suum in vitro. These results indicate that the effects of vasopressin and nitroglycerin on antigen-induced airway smooth muscle contraction in vivo were due to alterations in airway blood flow rather than to alterations in the release of or airway smooth muscle responsiveness to chemical mediators.
ASJC Scopus subject areas
- Pulmonary and Respiratory Medicine