Pharmacological Study on the Possible Roles of Platelet-activating Factor (PAF) in Inflammatory Process of the Dental Pulp

本研究的目的是确定牙髓组织中是否产生血小板活化因子（PAF），并评估PAF在牙髓炎症过程中的可能作用。首先，利用兔洗血小板建立了PAF的生物检测系统。这种生物测定系统使我们能够在聚集测定管中检测低至2.5 pg的PAF。取大鼠门牙分离牙髓组织，加或不加10 m钙离子载体A23187孵育30 min。用薄层色谱法提取和纯化脂质，测定血小板聚集活性。A23187刺激，虽然轻微，诱导血小板聚集活性的产生。这种聚集活动通过几个标准被确定为PAF。然而，乙酰辅酶a和PMSF这两种被称为PAF生物合成刺激剂都不能增加a23187诱导的PAF的产生。此外，凝血酶和组胺都不能诱导髓组织产生PAF，而这些物质却能刺激培养的人血管内皮细胞产生PAF。[^3H]PAF与牙髓组织孵育后，PAF被代谢为溶解PAF和酰基pfc，另一方面，PAF刺激牙髓组织时，促进前列腺素（PF） l2和血栓素（TX） A_2的产生。尽管介导PGL_2和TXA_2产生的PAF受体亚型不同，但这种刺激作用被几种特异性拮抗剂所抑制。两种代谢物对钙离子的依赖程度不同，刺激作用的确切机制也可能不同。这些发现表明PAF可能通过与花生四烯酸代谢物相互作用在牙髓炎症过程中产生并发挥重要作用。为了确定PAF在牙髓炎症中的确切作用，还需要进行牙髓炎症模型的体内研究。

The aim of the present research program was to determine whether platelet-activating factor (PAF) was produced in dental pulp tissue and to evaluate the possible role of PAF in pulp inflammatory process. At first, the bioassay system for the detection of PAF was established by using rabbit washed platelets. This bioassay system enabled us to detect as low as 2.5 pg PAF in an aggregation assay tube. Dental pulp tissues isolated from rat incisors were incubated for 30 min with or without 10 m calcium ionophore A23187. Lipids were extracted and purified by thin layer chromatography, and the platelet-aggregating activity was determined. A23187 stimulation, although slightly, induced the production of platelet-aggregating activity. This sggregating activity was identified as PAF by several criteria. However, neither acetyl CoA nor PMSF, known as stimulants of PAF biosynthesis, increased A23187-induced PAF production. Further, neither thrombin nor histamine induced PAF production by the pulp tissue, whereas these substances stimulated PAF production by human vascular endothelial cells in culture.When [^3H]PAF was incubated with pulp tissue, PAF was metabolized to lyso PAF and acyl PFC. On the other hand, when dental pulp tissue was stimulated by PAF, the production of prostaglandin (PF) L_2 and thromboxane (TX) A_2 was stimulated. This stimulatory effect was inhibited by the several specific antagonists although the PAF receptor subtype mediating PGL_2 and TXA_2 production seemed to be different. The precise mechanism of the stimulatory effect may be also different between the two metabolites in terms of the dependency on calcium ions. These findings suggest that PAF may be produced and has important roles by interacting with arachidonate metabolites in the pulp inflammatory process. The in vivo study using pulp inflammatory model would be required to confirm the precise roles of PAF in the inflammation of the bental pulp.