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. In travenous 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 vas cular conductance increased by 76 +/- 22%. In contrast, aerosolized ac etylcholine 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 th ere was no further increase in conductance when the aerosolized dose w as increased to 2,000 mu g/kg. Pretreatment of animals with a nitric o xide synthase inhibitor, N omega-nitro-L-arginine methyl ester hydroch loride, partially blocked the vasodilatory effects of intravenous acet ylcholine and completely blocked the vasodilatory effects of high-dose aerosolized acetylcholine. These data suggest that aerosolized acetyl choline does not readily penetrate the vascular wall of bronchial circ ulatory system and, therefore, has minimal vasodilatory effects on the bronchial vasculature.