Acute inflammation enhances substance P-induced plasma protein extravasation in the rat knee joint.

Acute inflammation of the rat knee joint was induced by intra-articular injection of 2% carrageenan. Intra-articular perfusion of the inflamed joint with substance P (SP) exacerbated the inflammatory condition as assessed by the degree of plasma protein extravasation into the synovial cavity. Protein extravasation induced by SP was enhanced and more persistent in the inflamed rat knee compared to normal animals. The time course of the response in the inflamed rat knee was related to SP concentration whilst the persistency of the response was positively correlated with the initial level of joint inflammation.