Tityus serrulatus venom (Tsv)-induced pulmonary edema can occur in severe envenomation and the mechanisms involved are not completely understood. Therefore, we studied the effect of pharmacological modulation of the mast cell activation and the histamine antagonism on airways edema (investigated by Evans blue dye extravasation) and measured 5-hydroxytryptamine (5-HT) concentration in bronchoalveolar lavage fluid (BALF) in rats envenomed by Tsv. Additionally, the in vitro effect of Tsv on mast cells was studied using histological method and 5-HT release from mesenteric and peritoneal mast cells. We found that i.v. injection of Tsv increase vascular permeability in trachea, upper and lower bronchi and in lung parenchyma. This was not affected by ketotifen, a mast cell "stabilizer," or by pretreatment with pyrilamine (histamine H1 receptor antagonist). Moreover, 5-HT was not found in BALF of envenomed rats. In vitro experiments showed that Tsv did not induce mast cell degranulation nor release of 5-HT by mesenteric or peritoneal mast cells, in sharp contrast to preparations challenged by a mast cell activator, compound 48/80. In conclusion, our results show that Tsv causes strong edema in rat airways which is independent of mast cell activation and show that mast cells are not directly activated by Tsv.
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