Role of mediators in allergic and nonallergic asthma in dogs with hyperreactive airways

Basenji-Greyhound crossbreed dogs, with nonspecific airway hyperreactivity, release histamine into the plasma after aerosol challenge with Ascaris antigen and a slow reacting substance (SRS) after aerosol challenge with citric acid or Ascaris antigen. The appearance of SRS in the plasma after citric acid aerosol challenge, without an increase in histamine, closely parallels the changes in pulmonary mechanics. The pulmonary response to citric acid, in contrast to Ascaris antigen, is totally prevented in vivo by FPL 55712, an SRS antagonist. SRS exhibits both pharmacologic properties and chemical characteristics similar to leukotrienes. These studies suggest that SRS may be an important mediator in nonallergic airway constriction in vivo.