Modification by capsaicin and compound 48/80 of dye leakage induced by irritants in the rat.

Concentration-related dye leakage produced by intracutaneous injections of irritants was measured in rats by an Evans blue technique. 2 In rats pretreated with a total dose of 50 mg capasaicin over 4 days, the response to capsaicin, formalin, HCl, KCl, prostaglandin E1, bradykinin and bradykinin with prostglandin E1 (10(-6) M) were greatly reduced, the responses to histamine and 5-hydroxytryptamine were slightly reduced and those to adenosine 5'-triphosphate (ATP) and compound 48/80 were unaffected. 3 Pretreatment with intracutaneous injections of compound 48/80 (0.5 mug, 24 and 48 h previously) recuded the responses to ATP, compound 48/80, HCl, KCl, prostaglandin E1, and bradykinin but did not affect those to histamine, 5-hydroxytryptamine or bradykinin with prostaglandin E1 (10(-6) M). 4 Responses to capsaicin and formalin produced spotted blueing extending over a large area and were suppressed by compound 48/80 in the smaller pretreated area only. Capsaicin responses were reduced with larger doses of compound 48/80 (total dose 15 mug). 5 It is concluded that the production of neurogenic oedema involves both sensory nerves and mast cells.