Prostaglandin synthesis does not mediate the pulmonary vasodilatory effect of acetylcholine

We wondered if inhibition of hypoxic pulmonary vasoconstriction by acetylcholine was mediated by prostaglandin synthesis. In 5 calves at a simulated altitude of 4,570 m, acetylcholine (10 mug/kg/min) decreased mean pulmonary arterial pressure and total pulmonary resistance by 24 +/- 2 and 35 +/- 3% before and by 21 +/- 2 and 27 +/- 4% after the administration of meclofenamate (2 mg/kg). Since there was no difference in the effect of acetylcholine before and after meclofenamate, it was concluded that pulmonary vasodilation by activation of muscarinic receptors was not dependent on prostaglandin synthesis.