Characterization of a late phase pulmonary response after antigen challenge in allergic sheep.

We determined if allergic sheep undergo a dual bronchoconstriction in response to inhalation of antigen and whether these responses could be modified by cromolyn or glucocorticosteroids. In 8 conscious sheep with Ascaris suum hypersensitivity, mean pulmonary flow resistance (RL), dynamic lung compliance (Cdyn), thoracic gas volume (Vtg), and arterial oxygen tension (PaO2) were determined prior to, immediately after, and from 2 through 8 h after and 24 h after inhalation challenge with Ascaris suum antigen. Immediately after antigen challenge, mean specific lung resistance (SRL = RL X Vtg) increased by 750% (p less than 0.01) and mean Cdyn and PaO2 decreased by 55% (p less than 0.01) and 37% (p less than 0.01), respectively. By 5 h after challenge, mean SRL and PaO2 had returned to baseline values, whereas mean Cdyn was still below baseline (-19%, p less than 0.05). At 6.5 h, mean SRL increased again to 245% (p less than 0.01) of baseline and remained significantly elevated through the eighth hour. The average increase in mean SRL for the 6.5- to 8-h postchallenge period was 196%, with concomitant decreases in mean Cdyn and PaO2 of 29% and 10%, respectively. By 24 h, all values had returned to baseline. Control inhalation challenge with ragweed, an antigen to which sheep are not sensitive, did not significantly alter SRL, Cdyn, or PaO2 at any time during the 8-h observation period, indicating that the late response was antigen specific and not caused by circadian rhythm.(ABSTRACT TRUNCATED AT 250 WORDS)