血小板激活因子和银杏内酯B对洗涤兔血小板中cAMP含量的影响

研究了血小板激活因子(PAF)和PAF拮抗剂银杏内酯B对洗涤兔血小板中cAMP含量的作用. 结果表明PAF(0.1-1.0 μmol·L^-1)对血小板的基础cAMP水平无影响, 但对前列腺素E₁(PGE₁) 2 μmol·L^-1及4,5-二氢-6-［4-(1H-咪唑-1)苯基］-5-甲基-3-(2H)-哒嗪酮(CI-930) 20 μmol·L^-1引起的cAMP升高有显著的抑制作用. 银杏内酯B能完全拮抗PAF抑制PGE₁和CI-930升高cAMP的作用, IC₅₀分别为4.7和12.5 μmol·L^-1. 合用磷酸肌酸/磷酸肌酸激酶和阿司匹林对PAF和银杏内酯B的作用均无影响. 提示PAF对磷酸二酯酶的激活作用及腺苷酸环化酶的抑制作用是PAF的直接作用，与其同PAF受体结合有关.

Effects of platelet activating factor and ginkgolid B on the cAMP levels in washed rabbit platelets

Effects of platelet activating factor (PAF) and PAF antagonist ginkgolid B on the cAMP levels of washed rabbit platelets were studied. The results showed that PAF (0.1-1.0 μmol·L^-1) had no effect on the basal cAMP level (0.9±0.1 pmol/10⁸ platelets) of rabbit platelets, but partially inhibited the increase in cAMP level induced by addition of 2 μmol·L^-1 prostaglandin E₁ (PGE₁) or 20 μmol·L^-1 4,5-dihydro-6-［4-(1H-imidazol-1-yl)phenyl］-5-methyl-3(2H)-pyridazinone (CI-930, a phosphodiesterase Ⅲ inhibitor). The inhibitory effects of PAF on cAMP levels in platelets (treated with PGE₁ or CI-930) were completely reversed by adding of ginkgolid B, the IC₅₀ values of ginkgolide B on PAF effect in platelets treated with PGE₁ or CI-930 were 4.7 and 12.5 μmol·L^-1, respectively. Adding phosphocreatine/creatine phosphokinase (0.7 mmol·L^-1/40 kU·L^-1) or aspirin (100 μmol·L^-1) did not change the effects of PAF and the combination of PAF with ginkgolid B. These data suggest that PAF binding to its receptor may be responsible for the activation of cAMP phosphodiesterase or inhibition of adenylate cyclase in rabbit platelets.