This study was performed to elucidate the analgesic mechanism of paradol and to compare effects of paradol with those of dihidrocapscaicin(DHC).
Rabbits(22.5kg both sexes) were anesthetized with pentobarbital sodium(30mg/kg IN.), and ca.nnulated in trachea and external jugular vein. To observe effects on jaw opening re-flex, inferior alveolar nerve(IAN) of both sides were exposed for drug application, and wire electrodes were inserted in anterior belly of digastric muscle for recording of EMGs of anterior belly of digastric mucscle(dE;MG) and in oral mucosa covering mental foramen for applying noxious stimulation. dEMGs evoked by noxious stimulation with double intensity of threshold for digastric EMG were recorded in magnetic tape recorder. To observe effects on action potential, saphenous nerve were exposed, and three tissue pools were made from "surrounding tissue. The most distal pool was used for applying stimulation, the most proximal one for recording of action potentials, and the other one for drug application. Action potentials evoked by 200 folds intensity of threshold for most sensitive fiber were recorded in magnetic tape recorder. One side of IAN and saphenous nerves were used for DHC or paradol applications, the other side of nerves for control experiments (only vehicle application). Vehicle consisted of 10% Tween 80, 1096 ethanol and 80% physiological saline(v/v), and drugs were solubilized in vehicle for 1.5% concentration(w/v). dEMGs and action potentials were recorded before drug application, immediate after 30 minutes drug application, at 30 and 60 minutes after drug had been washed out.
DHC application on IAN could not influence on dEMG, but paradol application decreased the amplitude of dEMG. In action potential experiments, DHC decreased amplitude and conduction velocity of only C fiber, while paradol did those of Cfiber and AS fiber.
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