The present study was designed to investigate the role of bradykinin (BK) in the knee joint osteoarthritis induced by intraarticular (i.ar.) administration of monosodium iodoacetate (MIA) in the rat, and to determine the efficacy of the kinin B 2 receptor antagonists, 4-(S)-amino-5-(4-{4-[2,4-dichloro-3-(2,4-dimethyl-8-quinolyloxymethyl)phenylsulfonamido]-tetrahydro-2H-4-pyranylcarbonyl} piperazino)-5-oxopentyl](trimethyl)ammonium chloride hydrochloride (MEN16132) and icatibant, in reducing pain. Rats received MIA (1 mg/25 l i.ar.) in the right knee. MEN16132, icatibant (1, 3, and 10 g/25 l i.ar.), or saline were administered 7 days after MIA treatment, and their antinociceptive effect was observed for 2 weeks. MEN16132 induced a marked and sustained reduction of incapacitation produced by MIA, approximately 56% inhibition of pain at 3 g/knee. MEN16132 analgesia was more potent and longer lasting, up to 10 days, than icatibant. MEN16132 (3 g/knee), at different time points from MIA treatment in separate groups of animals, produced comparable maximal antinociceptive effects, whereas the pain response induced by MIA was unaffected if MEN16132 (10 g/knee) was administered in the contralateral knee. Indomethacin at high doses (100 -625 g/knee) inhibited by approximately 40% but with a short duration the MIAinduced pain. MIA treatment produced a significant increase of BK and prostaglandin E 2 (PGE 2 ) metabolite levels in synovial fluid up to 21 days, and PGE 2 metabolite levels were reduced almost to basal values by MEN16132. In conclusion the potent and long-lasting analgesic effect of MEN16132 in MIA-induced osteoarthritis indicates an important role for BK in osteoarthritic pain, and suggests that MEN16132 can be a candidate for the treatment of this chronic disease.Osteoarthritis (OA) is a degenerative joint disease that affects most of the elderly population causing chronic pain and joint disability. In particular, the OA of the knee is characterized by histological changes of the joint involving degeneration of articular cartilage with fibrillation and erosion, synovitis, remodeling of subchondral bone with osteophytes formation at the joint margins, and sclerosis of subchondral bone (Goldring and Goldring, 2007). The pathophysiology behind these modifications is complex and involves a combination of mechanical, cellular, and biochemical processes that are not yet completely understood. Inflammation contributes to increase structural degeneration by releasing catabolic and proinflammatory mediators including cytokines, nitric oxide, and matrix metalloproteinases that may activate chondrocytes and synovial fibroblasts leading to cartilage destruction (Goldenberg et al., 1982;Yasuda, 2006;Sutton et al., 2009). No drug modifying OA progression is currently available, and treatment options are focused on symptomatic relief of pain and inflammation to improve the joint function. Nonsteroidal anti-inflammatory drugs (NSAIDs), corticosteroids, and opiates are widely used, but Article, publication date, and c...