[Effects of prostaglandin E2 and sodium hyaluronate on bradykinin induced knee joint pain in rat].

We studied effects of prostaglandin E2 and sodium hyaluronate on the reactive muscle activity induced by intra-articular injection of bradykinin into the knee joint of rat. An animal model was developed to evaluate knee joint pain. In unanesthetized and spinalized rat, bradykinin (BK) was injected into the knee joint and the duration of the reactive activity of the knee flexor was evaluated. The duration of the reaction was elongated dependent on the injected BK dosage (0.025-2.5 micrograms). When prostaglandin E2 (PG E2) was injected with BK, the duration of the reaction increased significantly (p < 0.01). In contrast, sodium hyaluronate (Na-HA: average MW 900 kD) injected into the joint 3-24 hours in advance significantly inhibited the BK induced reaction (p < 0.05-0.01). A histological study demonstrated the fluorescein-labeled Na-HA diffusely infiltrating into the surface of the soft tissue. From these results, the animal model used in the present study was valuable to evaluate quantitatively knee joint pain. Furthermore, the sensitizing effect of PG E2 and the inhibitory effect of Na-HA on joint pain was objectively demonstrated.