Nitric oxide modulates articular sensory discharge and responsiveness to bradykinin in normal and arthritic rats in vivo

Nitric oxide is implicated in peripheral nociceptive processing. This study determined the effects of the nitric oxide synthase inhibitor, L-NAME, on neural discharge from articular C-fibre afferents innervating normal and ar thritic ankle joints in anaesthetized rats. Intra-arterial injection of L-N AME (10-20 mg kg(-1)) increased neural discharge in normal and arthritic an kle joints, whereas D-NAME (30 mg kg(-1)) had no effect. The excitation ind uced by L-NAME (20 mg kg(-1)) was reduced by co-injecting the nitric oxide precursor, L-arginine (50 mg kg(-1)). L-NAME (20 mg kg(-1)) also enhanced r esponsiveness to bradykinin (10 mug) but only in arthritic rats, whereas L- arginine (50 mg kg(-1)) reduced the excitation by bradykinin (30 mug) in bo th groups. These results provide evidence that nitric oxide modulates artic ular C-fibre activity and reduces responsiveness to bradykinin. NeuroReport 12:121-125 (C) 2001 Lippincott Williams & Wilkins.