Accelerated acetylcholine metabolism in the lung after infusion of phenylephrine in dogs.

We investigated whether continuous administration of an a-adrenergic agonist, phenylephrine, could affect acetylcholine metabolism within the pulmonary circulation in anesthetized dogs. Infusions of phenylephrine at 3 microg/kg/min for 120 min shifted the dose-response curve for the depressor responses produced by acetylcholine (0.03-10 micro g/kg) injected into the right atrium to the right by about 30-fold. In contrast, the magnitude of the rightward shift in the dose-response curve for the depressor responses produced by acetylcholine injected into the left ventricle was only 3-fold. These results suggest that continuous administration of alpha-adrenergic agonists accelerate acetylcholine metabolism within the pulmonary circulation.