Differential modulation of cell recruitment and acute edema in a model of Polybia paulista venom-induced inflammation

Hymenoptera stings are quite common and can cause inflammatory reactions (in nonallergic individuals) or serious reactions (in allergic individuals). Hymenoptera venom contains histamine, vasoactive kinins, serotonin, phospholipase A, phospholipase B, hyaluronidase, antigen 5 and mastoparans. Some of these substances are responsible for local pain, as well as for activation of complement and endothelial cells. Polybia paulista is a wasp typically found in the state of São Paulo, Brazil. In the present study, we evaluated inflammatory reactions in the peritoneal cavities of rats injected with P. paulista venom (PPV). We evaluated leukocyte recruitment and edema formation at the site of inflammation. After i.p. inoculation with PPV, there was dose-dependent and time-dependent recruitment of neutrophils, eosinophils and mononuclear cells. At 4 to 48 h after stimulus, administration of MK 886, a leukotriene synthesis inhibitor, completely abolished granulocyte recruitment to the peritoneal cavity. Therefore, leukotrienes seem to be the primary mediators of PPV-induced neutrophil and eosinophil recruitment. Inoculation with PPV also induced protein extravasation into the peritoneal cavity. This phenomenon was not inhibited by treatment with MK 886 or indomethacin (a prostaglandin synthesis inhibitor), demonstrating that neither leukotrienes nor prostaglandins are involved in this inflammatory reaction. However, edema formation was significantly inhibited by treatment with pyrilamine, indicating that the histamine H1 receptor plays a critical role in PPV-induced formation of acute edema.