Antinociceptive Activities of Some 4,5-Dihydro-1H-Pyrazole Derivatives: Involvement of Central and Peripheral Pathways

This study was planned to investigate possible antinociceptive activity of 1,5-diaryl-3-[4- (methylsulfonyl)phenyl]-4,5-dihydro-1H-pyrazole derivatives (2a-s), based on the analgesia-inducing potential of 4,5-dihydro-1H-pyrazole moiety carrying compounds. Tail-clip and hot-plate tests, measuring centrally organized responses to a noxious stimulus, were performed in order to examine antinociceptive potential of the test compounds (100 mg/kg, i.p). In addition, peripherally mediated antinociceptive effect was evaluated by acetic acid-induced writhing tests. Motor coordination of the animals was tested in a Rota-rod apparatus. Among the tested compounds 2c, 2e, 2g, 2h, 2j, 2l, 2m, 2o and 2r prolonged the reaction time, measured in the tail-clip and hot-plate tests, with respect to the control values. The same compounds also decreased the quantity of acetic acidinduced writhing behaviours. In the Rota-rod tests, compound 2r was the only derivative decreasing the falling latency of mice. The obtained results indicated that some of the tested 4,5-dihydro-1H-pyrazole derivatives induce notable antinociceptive activity by effecting both of the central and peripheral nociceptive pathways. In addition, this study provided some information about structure-activity relationship for the compounds carrying similar chemical scaffold. Nevertheless, it should be noted that mechanism of action for these agents should be clarified with further detailed investigations.