Resiniferatoxin reversibly blocks adjuvant-induced thermal hyperalgesia in the rat.

The role of capsaicin-sensitive sensory afferents and mast cells in complete Freund's adjuvant (CFA)-induced thermal hyperalgesia and edema was investigated in rats. A single systemic injection of resiniferatoxin produced a reversible prevention of adjuvant-induced thermal hyperalgesia which lasted several days. In addition, resiniferatoxin markedly reduced the early edema. Chronic degranulation of mast cells with compound 48/80 also reduced the thermal hyperalgesia and edema, especially in the early phase of inflammation. Co-pretreatment with resiniferatoxin and compound 48/80 induced effects similar to those of resiniferatoxin alone. The data support the involvement of capsaicin-sensitive fibers in the adjuvant-induced inflammation.