Abstract
The analgesic mechanism of Y-23023, a new non-steroidal anti-inflammatory drug, was investigated in the writhing response induced by intraperitoneal injection of kaolin and captopril in mice. Y-23023 (0.1-1 mg/kg, p.o.) suppressed the writhing frequency in a dose-dependent manner. Y-23023 also significantly reduced the increased levels of prostaglandin (PG) and bradykinin (BK) in the peritoneal cavity. In contrast, indomethacin, diclofenac sodium, loxoprofen sodium and mefenamic acid inhibited the writhing response, but their efficacies were lower than that of Y-23023. The peritoneal PG levels were dose-dependently reduced to the same extent as Y-23023, whereas the BK levels were not. M1, an active metabolite of Y-23023, inhibited the cyclooxygenase from sheep vesicular gland in a concentration-dependent manner, and its potency was similar to that of indomethacin. These results suggest that in addition to the suppressive effect on PG production via inhibition of cyclooxygenase, the inhibitory effect on BK production is involved in the analgesic action of Y-23023, unlike indomethacin and diclofenac sodium.
