Effects of capsaicin on inflammation and on the substance P content of nervous tissues in rats with adjuvant arthritis.

Capsaicin (20-80 mg/kg, s.c.) reduced the inflammatory response to inoculation with Mycobacterium butyricum in the rat. The effect was apparent within 24 h, was partial, persisted for well over 20 days, and occurred irrespective of whether capsaicin was administered before or after the onset of inflammation, or at the time when the pathology reached peak. Capsaicin also attenuated the increase in substance P content in sciatic nerve, saphenous nerve, dorsal root ganglia, dorsal roots, and dorsal spinal cord (L4, L5) which occurs in rats with adjuvant arthritis. The data are consistent with a possible role of substance P in the peripheral manifestations of adjuvant arthritis.