The effect of the dihydropyridine, platelet activating factor (PAF) receptor antagonist, UK-74,505, on leucocyte accumulation and oedema formation in guinea-pig skin was investigated. The inflammatory reactions studied were elicited by exogenous mediators, a passive cutaneous anaphylactic (PCA) reaction and zymosan particles. 2. Leucocyte accumulation and oedema formation were measured as the local accumulation of i.v. administered 111In-labelled neutrophils or eosinophils together with 125I-labelled albumin. UK-74,505 was either administered i.v. or used to pretreat the radiolabelled leucocytes in vitro prior to their last wash and injection into recipient animals. 3. In vitro, UK-74,505 inhibited PAF-induced elevations in cytoplasmic levels of Ca2+ ([Ca2+]i) in fura-2-loaded guinea-pig neutrophils and eosinophils with IC50 values of 10(-9) M and 7 x 10(-9) M respectively. Neutrophils and eosinophils pretreated with 10(-7) M and 10(-6) M UK-74,505 respectively, and maintained at 37 degrees C, were unresponsive to PAF for the 4 h period investigated. 4. In vivo, using 2 h test periods, i.v. UK-74,505 (0.5 and 2.5 mg kg-1) inhibited the accumulation of 111In-neutrophils, 111In-eosinophils and oedema formation induced by intradermal PAF, but had no effect on responses elicited by leukotriene B4 (LTB4) and zymosan-activated plasma (ZAP, used as a source of C5a des Arg). UK-74,505 (2.5 mg kg-1) was also without an effect on response induced by a PCA reaction but significantly suppressed the 111In-eosinophil accumulation following the intradermal administration of zymosan particles. The 111In-neutrophil accumulation induced by zymosan particles was not, however, affected by UK-74,505. 5. In a second series of in vivo experiments, "'In-leucocytes were pretreated in vitro with UK-74,505 prior to their last wash and injection into recipient animals. Radiolabelled neutrophils, and eosinophils were pretreated with 10-7 M and 10-6 M UK-74,505 respectively, concentrations previously shown to block the leucocyte responses to PAF in vitro for up to 4 h. The in vitro pretreatment of the cells with the PAF antagonist, whilst not affecting the responses to intradermally-injected PAF, suppressed the"'In-eosinophil accumulation response induced by zymosan particles.6. The results of this study indicate that PAF is not involved in neutrophil accumulation, eosinophil accumulation and oedema formation induced by LTB4, ZAP and a PCA reaction. Endogenous PAF does, however, appear to have a role in zymosan-induced eosinophil accumulation but not neutrophil accumulation, suggesting the existence of different inflammatory pathways in the induction of neutrophil and eosinophil accumulation in vivo. Furthermore, while leucocyte accumulation induced by exogenous PAF does not appear to involve leucocyte PAF receptors, the mechanism by which endogenous PAF mediates the zymosan-induced eosinophil accumulation appears dependent on the expression of PAF receptors on eosinophils.
摘要
研究了二氢吡啶类血小板活化因子（PAF）受体拮抗剂UK-74,505对豚鼠皮肤白细胞聚集和水肿形成的影响。所研究的炎症反应由外源性介质、被动皮肤过敏反应（PCA）和酵母聚糖颗粒引发。2. 通过静脉注射111In标记的中性粒细胞或嗜酸性粒细胞以及125I标记的白蛋白的局部聚集来测量白细胞聚集和水肿形成。UK-74,505通过静脉注射给药，或在放射性标记的白细胞最后一次洗涤并注射到受体动物之前用于体外预处理。3. 在体外，UK-74,505抑制PAF诱导的fura-2负载的豚鼠中性粒细胞和嗜酸性粒细胞胞质Ca2+水平（[Ca2+]i）升高，IC50值分别为10^(-9) M和7×10^(-9) M。分别用10^(-7) M和10^(-6) M UK-74,505预处理的中性粒细胞和嗜酸性粒细胞，在37℃下维持，在研究的4小时内对PAF无反应。4. 在体内，使用2小时测试期，静脉注射UK-74,505（0.5和2.5 mg kg-1）抑制皮内注射PAF诱导的111In-中性粒细胞、111In-嗜酸性粒细胞聚集和水肿形成，但对白细胞三烯B4（LTB4）和酵母聚糖激活的血浆（ZAP，用作C5a去精氨酸的来源）引发的反应无影响。UK-74,505（2.5 mg kg-1）对PCA反应诱导的反应也无影响，但显著抑制皮内注射酵母聚糖颗粒后111In-嗜酸性粒细胞的聚集。然而，酵母聚糖颗粒诱导的111In-中性粒细胞聚集不受UK-74,505影响。5. 在第二系列体内实验中，111In-白细胞在最后一次洗涤并注射到受体动物之前在体外先用UK-74,505预处理。放射性标记的中性粒细胞和嗜酸性粒细胞分别用10^(-7) M和10^(-6) M UK-74,505预处理，先前已证明这些浓度可在体外长达4小时阻断白细胞对PAF的反应。用PAF拮抗剂对细胞进行体外预处理，虽然不影响对皮内注射PAF的反应，但抑制了酵母聚糖颗粒诱导的111In-嗜酸性粒细胞聚集反应。6. 本研究结果表明，PAF不参与LTB4、ZAP和PCA反应诱导的中性粒细胞聚集、嗜酸性粒细胞聚集和水肿形成。然而，内源性PAF似乎在酵母聚糖诱导的嗜酸性粒细胞聚集中起作用，但在中性粒细胞聚集中不起作用，这表明在体内中性粒细胞和嗜酸性粒细胞聚集的诱导中存在不同的炎症途径。此外，虽然外源性PAF诱导的白细胞聚集似乎不涉及白细胞PAF受体，但内源性PAF介导酵母聚糖诱导的嗜酸性粒细胞聚集的机制似乎依赖于嗜酸性粒细胞上PAF受体的表达。
