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

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Abstract
Platelet-activating factor (PAF-acether) is a potent agonist (EC50: 3.2 × I0−8 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 × 10−5 M). Salbutamol (IC50: 3.1 × 10−7 M), forskolin (IC50:3.1 × 10−6M) and theophylline (IC50: 2.25 × 10−4M) 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 × 10−7M), forskolin (IC50: 2.6 × 10−4M) and theophylline (IC50: 2.3 × 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.