PAF INDUCES RELAXATION OF PULMONARY-ARTERIES BUT CONTRACTION OF PULMONARY VEINS IN THE FERRET

The present study was designed to determine whether platelet activatin g factor (PAF) has different effects on pulmonary arteries and veins. Third-order pulmonary arterial and venous rings of the ferret were sus pended in organ chambers filled with modified Krebs-Ringer bicarbonate solution (95% O-2-5% CO2, 37 degrees C) and their isometric tension w as recorded. Under basal conditions, PAF had no effect on the resting tension of arteries but induced an endothelium-dependent contraction o f veins. The contraction was not affected by BW-755C (an inhibitor of cyclooxygenase and lipoxygenase), BQ-123 [an antagonist of endothelin (ET) A (ET(A)) receptors)], or IRL-1038 (an antagonist of ET(B) recept ors). PAF had no effect on veins during contraction to prostaglandin F -2 alpha (PGF(2 alpha)) but induced an endothelium-dependent relaxatio n of arteries. The relaxation was abolished by N-omega-nitro-L-arginin e. Incubation with PAF for 30 min augmented contractions of veins with endothelium to PGF(2 alpha). The augmentation was not affected by BW- 755C, BQ-123, or IRL-1038. Pretreatment with PAF had no effect on the response of veins to phenylephrine or on the response of arteries to e ither PGF(2 alpha) or phenylephrine. These observations demonstrated t hat, in the ferret, PAF affected differently the response of pulmonary arteries and veins and that the endothelium plays a critical role in the PAF-induced effects. Furthermore, the PAF-induced effects appear n ot to be mediated by metabolites of arachidonic acid and ET.