Prostaglandins evoke a whole variety of responses in the lung

Rapid intravenous (IV) injections of the prostaglandin precursor arachidonic acid (AA) increase pulmonary arterial pressure (PAP) and pulmonary vascular resistance (PVR) in a variety of species. It has recently been reported that infusions of AA decrease PAP. The purpose of this report is to contrast responses to bolus injections and infusions of AA in the anesthetized dog. In all experiments rapid IV injections of AA increased PAP and PVR; however, infusions of 68 to 680 microgram/min produced variable responses. In 10 of 19 animals, AA infusion decreased PAP and PVR, and this response was enhanced when pulmonary vascular tone was actively increased by vasoconstrictor agents or alveolar hypoxia. In the other nine animals, the predominant response was an increase in PAP and PVR. In all experiments infusions of larger amounts of AA (1.4 to 3.4 mg/min) increased PAP. Both pressor and depressor responses to AA were inhibited to meclofenamate. This study shows that infusion of small amounts of AA dilates or constricts the pulmonary vascular bed. In contrast, infusion of larger amounts of AA always causes vasoconstriction. These data suggest that at low infusion rate, PGI2, which is a vasodilator, is the predominant metabolite formed from AA in some animals. However, at higher concentrations, the production of constrictor products predominates. These experiments also suggest that the products formed and the response observed may be dependent on a number of factors including the amount of tone present in the pulmonary vascular bed.