Effect of platelet-activating factor on porcine pulmonary blood vessels in vitro

Platelet-activating factor (PAF) induced contractions of porcine pulmonary vein strips in a concentration-dependent manner, while porcine pulmonary artery strips were unresponsive. Exposure to the specific PAF-antagonists WEB 2086 or BN 52021 antagonized the contractile responses of pulmonary vein strips. Cysteinyl-leukotrienes (LT) and thromboxane (TX) B2 were not detected in the bath fluid after stimulation with PAF suggesting that these eicosanoids as well as their precursors are not mediators of PAF-induced contractions of porcine pulmonary vein strips. Furthermore, PAF had no significant effect on 6-keto-prostaglandin (PG) F1a release and flurbiprofen did not affect the PAF response, while it inhibited the release of 6-keto-PGF1a. This indicates that PGI2 or any other cyclooxygenase product is unlikely to modulate or mediate the PAF response. Incubation experiments with fragments of pulmonary vascular tissues demonstrated spontaneous release of small amounts of cysteinyl-LT, TXB2 and 6-keto-PGF1a, which was significantly increased during incubation in the presence of ionophore A23187. While these results demonstrate the synthesizing capacity of the porcine pulmonary vascular tissues for various eicosanoids, PAF failed to stimulate eicosanoid release under these experimental conditions. We conclude that PAF causes contractions of porcine pulmonary vein strips, which are not mediated by cysteinyl-LT or cyclooxygenase products of arachidonate metabolism. The specific contractile effect of PAF on pulmonary veins, but not arteries, could contribute to the disturbances of the pulmonary circulation observed after injection of PAF or release of endogenous PAF, e.g. after administration of endotoxin.