Active constriction and dilatation in pulmonary circulation in response to acetylcholine.

Abstract

Summary and conclusionsThe effects of acetylcholine on pulmonary vascular bed of intact dogs were studied in an experiment in which the drug could be excluded from the systemic circulation. While larger doses (usually greater than 0.1 mg) injected into the pulmonary artery were followed by increased pulmonary vascular resistance, smaller doses lowered pulmonary vascular resistance. Exclusion of extrapulmonary factors indicated active pulmonary vasoconstriction and vasodilatation. The larger doses also caused bronchomotor activity. However, the lack of intratracheal pressure changes with pulmonary vasodilating doses of acetylcholine or vasoconstricting doses of norepinephrine, and the absence of pulmonary hypertension with nebulization of acetylcholine indicated that pulmonary vascular resistance alterations were not dependent upon changes in bronchomotor tone.