Synovial fluid inflammatory mediators and matrix metalloproteinase activity in inflamed joints. Synovial fluid (SF) levels of (a) prostaglandin E2 (PGE2), (b) substance P, (c) bradykinin, and (d) general matrix metalloproteinase (MMP) activity over time in inflamed intercarpal joints of horses (n = 6). Inflammation was induced at t = 0 by intra-articular injection of 0.5 ng Escherichia coli lipopolysaccharide. Data presented as the mean ± standard error of the mean. *P < 0.05, **P < 0.01, ***P < 0.001. RFU/s, relative fluorescence units/second.