Plasma extravasation by chemical mediators in rat skin and trachea: a role of neurogenic agents on tracheal edema formation.

The plasma extravasation inducing activities of several chemical mediators (allergic agents: histamine, leukotriene C4 (LTC4) and platelet activating factor (PAF); neurogenic agents: substance P, capsaicin and carbachol) have been investigated and characterized in rat skin and trachea. Substance P, histamine, LTC4 and PAF induced dose-dependent plasma extravasation in rat skin. The activities of these mediators in inducing tracheal plasma extravasation were very different from those in the skin reactions. When these mediators were injected intravenously, substance P induced severe plasma extravasation, and the activities of histamine and PAF were weaker than that of substance P. When injected intratracheally, only substance P and capsaicin induced tracheal plasma extravasation, while none of the allergic mediators tested caused any plasma extravasation in the trachea. Carbachol did not induce any plasma extravasation in either skin or trachea. These results indicate that the stimulation of afferent substance P-containing nerve fibers has a more important role in the induction of tracheal plasma extravasation than that of allergic chemical mediators.