Pressor responses to arachidonic acid in pump-perfused sheep lungs

The reported actions of arachidonic acid in the adult pulmonary circulation are controversial. Some authors reported that arachidonic acid causes only pulmonary vasoconstriction; others have found decreases in pulmonary vascular resistance with low-dose infusions. We have previously reported that arachidonic acid causes only pulmonary vasoconstriction in perinatal lambs during both normoxia and hypoxia. The effects of arachidonic acid on pulmonary vascular resistance were determined in adult sheep using an in situ pump-perfused left lower lung preparation. Arachidonic acid infusions (10.5-31.9 micrograms/kg . min) resulted in pulmonary vasoconstriction. The pulmonary vascular response to arachidonic acid was not altered by hypoxia or by infusion of PGF2 alpha. However, the pulmonary pressor response to hypoxia was increased by concomitant arachidonate infusions. Infusions of arachidonic acid during hypoxia resulted in systemic hypotension. Thus, pulmonary arachidonate metabolism appears to be unaffected by hypoxia or PGF2 alpha; however, hypoxia may enhance the formation of dilator PG's from the lung.