Effects of some autacoids on breathing and perfusion flow in the isolated perfused rat lung

The effects of three autacoids [5-hydroxytryptamine (5-HT), bradykinin and acetylcholine (Ach)) on breathing and pulmonary circulation were studied in the isolated perfused and ventilated rat lung after intravascular injection or intrabronchial instillation. 5-HT, bradykinin and Ach all caused a dose related reduction in breathing, after injection into the pulmonary artery, with Ach being the most potent. With regard to effects on the pulmonary circulation, a dose-related reduction in perfusate flow was noted with bradykinin and 5-HT with bradykinin being about 10 times more potent than 5-HT. Ach did not reduce or increase perfusate flow. After intrabronchial instillation only 5-HT caused reduced perfusate flow. Effects on breathing were difficult to evaluate with this route of administration. The isolated perfused and ventilated lung seems to be a usable model to simultaneously study effects on respiration and pulmonary circulation.