Effects of BN 52063 and other agents inhibiting platelet-activating factor-induced contractile responses in rat portal vein.

Platelet-activating factor (PAF-acether) is a potent agonist (EC50: 3.2 x 10(-8) M) of isolated rat portal vein. BN 52063 (composed of BN 52020, BN 52021 and BN 52022; molar ratio 2:2:1) specifically inhibits PAF-acether (10(-7) M) induced tone (IC50: 3.9 x 10(-5) M). Salbutamol (IC50: 3.1 x 10(-7) M), forskolin (IC50: 3.1 x 10(-6) M) and theophylline (IC50: 2.25 x 10(-4) M) are also effective in inhibiting PAF-acether-induced contractile responses and all excepting forskolin, show a certain specificity in this action. The basal myogenic activity of the rat portal vein is dose-dependently decreased by salbutamol (IC50: 1.2 x 10(-7) M), forskolin (IC50: 2.6 x 10(-6) M) and theophylline (IC50: 2.3 x 10(-4) M) whereas BN 52063 has no effect. The data suggest that rat portal veins possess specific PAF-acether receptors sensitive to BN 52063 and that PAF-acether effects could be inhibited by compounds which can bypass these putative receptors and modulate cAMP levels.