Roles of PMN Leucocytes, Platelets and Some Mediators in Rat Hind-paw Oedema Induced by Two Phospholipase A2 Enzymes From Trimeresurus mucrosquamatus Venom

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Abstract
Two phospholipase A2 (PLA2) enzymes, TMVPLA2 I and TMVPLA2 II, isolated from Trimerusurus mucrosquamatus venom induced rat hind-paw oedema. Recovered myeloperoxidase activity increased within 1 h and was greatly elevated in the rat paw 3–6 h after subplantar injection of these venom PLA2 enzymes. Methotrexate pretreatment significantly reduced not only the peripheral leucocyte count but also venom PLA2-induced paw oedema. In rat isolated PMN leucocyte suspension, venom PLA2 induced superoxide radical formation. Paw swelling caused by TMVPLA2 I or TMVPLA2 II was only slightly or not, respectively, reduced in the rats pretreated with anti-platelet plasma, which reduced peripheral blood platelet count by >96%, suggesting platelets are not involved. In isolated platelet preparation, TMVPLA2 I induced platelet activation in a concentration-dependent manner, while TMVPLA2 II had no effect. Pretreatment with diphenhydramine/methysergide greatly suppressed the oedematous responses caused by the two venom PLA2 enzymes; the residual responses were significantly further depressed by aspirin. The oedematous responses caused by the enzymes were also suppressed by FPL 55712, BW 755C, dexamethasone, superoxide dismutase/catalase, isoprenaline and terbutaline. However, BN 52021 and L 652731, both platelet aggregating factor antagonists, were not effective on these responses. Thus, in addition to histamine and 5-hydroxytryptamine release by the mast cells in PLA2-induced paw oedema (Wang & Teng 1990), the results of this study indicate minor, but significant, roles for neutrophils and inflammatory mediators including prostaglandins, leukotrienes and superoxide radicals.