The response phase--the first six hours after acute airway injury by SO2 inhalation: an in vivo and in vitro study.

We have identified an airway epithelial response following acute injury that cannot be termed 'repair' or 'regeneration'. It precedes these well characterized events and it is termed the 'response phase'. We tested the hypothesis that for the first 6 h following acute injury to the tracheal mucosa, the initial cellular events of the response phase will continue as in vivo even if the tissue is maintained in vitro in an Ussing chamber. The tracheal mucosa of anesthetized, intubated mongrel dogs was injured by the inhalation of SO2 500 ppm for 1 h (7 dogs); controls (3 dogs) breathed filtered, compressed air for 1 h. 4 dogs were killed, in pairs, at 1 and 6 h after 500ppm of SO2; their tracheas were removed and fixed for microscopic examination. 3 dogs were killed immediately after the SO2 exposure, their tracheas were removed and epithelium isolated from the posterior-membranous sheath was mounted in Ussing chambers in oxygenated, Krebs-Henseleit buffer (8 per dog with aperature area of 1.5 cm2). These tissues (and those from control dogs prepared identically) were fixed after 1 and 6 h incubation for microscopic examination. Epithelial damage was not observed in any controls but was in all tissues exposed to SO2. A wide spectrum of mucosal cell injury during the response phase was observed. The patterns of exfoliation noted were: individual cells, rows (several cells wide) of mucosal cells and entire regions (several hundred microns 2). At 1 h after exposure, in some lesions, the injury is difficult to assess because the tracheal surface was either blanketed in exfoliated cells or appeared in total disarray. By 6 h, the lesions were well defined and large flattened cells (130 microns 2 in surface area) covered the basement membrane in areas where mucosal cells had exfoliated. Some ciliated cells still remained attached at their base in these areas. These were the findings whether the tissues were taken fresh from the animal or have been maintained in Ussing chambers for up to 6 h. These results show that cellular repair of the tracheal epithelium can be studied in vitro during the first 6 h after injury, even if the injury has occurred in situ.