Effect of aerosolized acetylcholine on bronchial blood flow

We studied the effects of aerosolized as well as intravenous infusion of acetylcholine on bronchial blood flow in six anesthetized sheep. Intravenous infusion of acetylcholine, at a dose of 2 mu g/kg, increased bronchial blood flow from 45 +/- 15 (SE) to 74 +/- 30 ml/min, and vascular conductance increased by 76 +/- 22%. In contrast, aerosolized acetylcholine at doses of 2 and 20 mu g/kg decreased bronchial vascular conductance by similar to 10%. At an aerosolized dose of 200 mu g/kg, the bronchial vascular conductance increased by similar to 15%, and there was no further increase in conductance when the aerosolized dose was increased to 2,000 mu g/kg. Pretreatment of animals with a nitric oxide synthase inhibitor, N omega-nitro-L-arginine methyl ester hydrochloride, partially blocked the vasodilatory effects of intravenous acetylcholine and completely blocked the vasodilatory effects of high-dose aerosolized acetylcholine. These data suggest that aerosolized acetylcholine does not readily penetrate the vascular wall of bronchial circulatory system and, therefore, has minimal vasodilatory effects on the bronchial vasculature.