COMPARISON OF SYNOVIAL P-O2 AND SYMPATHETIC VASOCONSTRICTOR RESPONSESIN NORMAL AND ACUTELY INFLAMED RABBIT KNEE JOINTS

Experiments were performed to assess the effect of acute inflammation of the rabbit knee joint on the partial pressure of oxygen in synovial fluid (P-s,P-O2) and nerve-mediated vasoconstrictor responses of arti cular blood vessels. With the hypodermic needle oxygen electrode sited within the synovial cavity in the posterior region of the knee joint, mean (+/- S.E.M.) P-s,P-O2 was 37.4 +/- 3.6 mmHg (n = 10) in the infl amed group, which differed significantly (P < 0.05) from that occurrin g in the normal group from a different series (48.2 +/- 3.1 mmHg; n = 18). P-s,P-O2 was found to decrease with increasing depth of penetrati on of the oxygen electrode into the joint cavity of the inflamed knee, as in the normal knee. The lowest -values were observed close to arti cular cartilage. Absolute blood flow was measured using radiolabelled microspheres whilst relative changes in blood flow were assessed using laser Doppler flowmetry. The former technique showed that the inflame d joints had a significantly higher blood flow. Electrical stimulation of the posterior articular nerve (PAN) of the knee resulted in vasoco nstriction of knee joint blood vessels, which was accompanied by a red uction in P-s,P-O2. The frequency-response and voltage-response profil es to electrical stimulation of the PAN, although differing in magnitu de, showed a high degree of correlation between blood flow and P-s,P-O 2. The frequency-response profile to electrical stimulation of the PAN shifted to the right in inflamed joints compared with normal joints, suggesting a reduction in the efficacy of the sympathetic nervous syst em in regulating blood flow to the inflamed joints. Although the infla med joint had a higher blood flow, P-s,P-O2 was lower compared with th e normal joint. The results of this study show significantly altered b lood flow, P-s,P-O2 and nerve-mediated constrictor responses in the ac utely inflamed joint. These are related to the inflammatory response a nd may contribute to the pathogenesis of arthritis.