Anaphylaxis in the lung of cats actively sensitized to Ascaris antigen has been investigated in vivo and in vitro. 2. In vivo there was a 100% increase in airways resistance and a 50% decrease in dynamic lung compliance following intravenous challenge with Ascaris antigen. Prostaglandin F2alpha induced similar changes but with histamine only dynamic lung compliance was affected. (-)-Isoprenaline prevented these prostaglandin F2alpha- and histamine-induced changes and caused a delay of about 2 min in the onset of the mechanical changes following anaphylactic challenge. 3. In vitro the isolated lung strip contracted within seconds of challenge whereas there was a delay of 2 to 3 min in the onset of the tracheal anaphylactic response. (-)-Isoprenaline, (-)-adrenaline and (+/-)-noradrenaline reduced the magnitude of anaphylactic contractions of the isolated trachea but did not significantly affect those of the isolated lung strip. This indicated lack of inhibition of mediator release from the lung parenchyma. 4. Histamine was released from sensitized lung fragments following challenge with the Ascaris extract. This release constituted 6.3% of the total tissue histamine and was not inhibited by (-)-isoprenaline (1 micrometer). 5. (-)-Isoprenaline abolished 5-hydroxytryptamine (5-HT)-induced contractions of the isolated trachea but not those elicited in response to acetylcholine. The isolated lung strip responses to histamine, prostaglandin F2alpha and 5-HT were highly resistant to inhibition by (-)-isoprenaline.
