Concentrations of substance P and prostaglandin E-2 in synovial fluid of normal and abnormal joints of horses

Objective-To correlate substance P content of synovial fluid with prostagla ndin E-2 content, radiographic evidence of joint abnormality, and anatomic location of the joint for normal and osteoarthritic joints of horses. Sample Population-Synovial fluid from 46 normal joints in 21 horses and 16 osteoarthritic joints in 10 horses. Procedure-Normal and osteoarthritic joints were identified by clinical and radiographic examination, by response to nerve blocks, during scintigraphy or surgery, or by clinicopathologic evaluation. Substance P and prostagland in E-2 contents of synovial fluid were determined by radioimmunoassay. Radi o-graphs of joints were assigned a numeric score reflecting severity of les ions. Joints were assigned a numeric score reflecting anatomic location. Results-Median concentrations of substance P and prostaglandin E-2 were sig nificantly increased in osteoarthritic joints, compared with normal joints. A significant correlation was found between concentrations of substance P and prostaglandin E-2 in synovial fluid, but a correlation was not detected between substance P concentration in synovial fluid and anatomic location of the joint or between radiographic scores of osteoarthritic joints and co ncentrations of substance P or prostaglandin E-2. Conclusions and Clinical Relevance-A correlation existed between concentrat ions of substance P and prostaglandin E-2 in synovial fluid obtained from n ormal and osteoarthritic joints. However, content of substance P in synovia l fluid cannot be predicted by the radiographic appearance of the joint or its anatomic location. Substance P and prostaglandin E-2 may share an impor tant and related role in the etiopathogenesis of osteoarthritis, lending cr edence to the importance of neurogenic inflammation in horses.