Sulfur dioxide induced airway hyperreactivity in allergic sheep

The effects of a four‐hour exposure (via a Plexiglas hood) to sulfur dioxide (SO2) on airway reactivity was studied in both normal and allergic conscious sheep. Allergic sheep were defined as animals in whom inhalation of Ascaris suum extract resulted in an increase in mean pulmonary flow resistance (RL). Airway reactivity (δRL) was assessed by measuring the increase in RL after 18 breaths of 0.25% carbachol, from an initial value obtained after 18 breaths of buffered saline. RL and δRL were determined prior to, immediately after and 24 hours following SO2 exposure in three groups of sheep: six normal sheep exposed to 5 ppm SO2 (group A); six normal sheep exposed to 10 ppm SO2 (group B) and seven allergic sheep exposed to 5 ppm SO2 (group C). RL was not affected by SO2 exposure in any group but both groups B and C showed increases in δRL 24 hours after exposure. Since the increase in δRL was greater in group C than in either groups A or B, we conclude that allergic sheep have enhanced susceptibility to the injurious airway effects of SO2.