THE SCHULTZ-DALE RESPONSE OF SENSITIZED CANINE BRONCHIAL SMOOTH-MUSCLE

We wished to determine why in vitro agonist dose-response curves show reduced leftward shift (1/2-1 log dose units) in sensitized canine air way smooth muscle compared to curves elicited in vivo (2-3 log dose un it). The Schultz-Dale response was studied in sensitized dog tracheal (TSM) and bronchial (BSM) smooth muscle. Sensitized TSM challenged wit h specific antigen showed greater mechanical response, but only on exp osure to 300 mu g/ml; BSM responded to concentrations of ragweed as lo w as 0.001 mu g/ml. This result resolved the problem cited at the outs et. Control TSM and BSM showed no response. The response in BSM is med iated through histamine release, and to a smaller extent by acetylchol ine. With challenge release of histamine and acetylcholine increased s ignificantly in sensitized airway smooth muscle. Integrated contractil e responses obtained with high and low concentrations of antigen showe d a dose-response relationship. Increased sensitivity of BSM to antige n compared to TSM indicates the former is the preparation of choice fo r study of allergic bronchoconstriction.