Inhibitory effects of orally taken etomidate on nociceptive stimulation in rats

    LI Zhen, LUO Ceng, WANG Liª²Yun, CHEN Jun

    1Pain Research Center, Institute of Neuroscience of Chinese PLA, Fourth Military Medical University, Xi¡¯an 710033, China, 2Department of Anesthesiology, 464 Hospital of Chinese PLA, Tianjin 300162, China

    ¡¾Abstract¡¿ AIM: To investigate whether orally taken etomidate has any inhibitory effects on the tissue injury induced pain in rats. METHODS: Subcutaneous formalin or bee venom injection was administrated into the plantar surface of one hindpaw. Spontaneous nociceptive response was immediately scored by counting the number of flinches of the injected hindpaw at every 5ª²minute interval during a 60ª²minute period. Thermal hyperalgesia was measured by recording the paw withdrawal reflex latency to heat stimulus by a radiant heat stimulator. The paw withdrawal thermal latency (PWTL) was determined as the duration from start of the thermal stimulation to the occurrence of the hindpaw withdrawal reflex and was averaged from four heat stimuli. Mechanical hyperalgesia was measured with von Freyª²type nylon filaments. The occurrence of 50% frequency of paw withdrawal was expressed as the paw withdrawal mechanical threshold (PWMT) averaged from 10 times stimuli. RESULTS: Orally taken etomidate 5 mg/kg only inhibited the phaseª²2 of persistent spontaneous pain induced by subcutaneous formalin injection. With higher doses, etomidate inhibited both the phases 1 and 2 of persistent spontaneous pain induced by subcutaneous formalin injection. Orally taken etomidate also doseª²dependently inhibited persistent spontaneous pain induced by subcutaneous bee venom injection. However, the reduction in PWTL and PWMT induced by bee venom was not influenced by etomidate. CONCLUSION: Orally taken etomidate is effective in the inhibition of the persistent spontaneous pain induced by both formalin and bee venom injection, while it is ineffective in the suppression of the heat and mechanical hyperalgesia induced by subcutaneous bee venom injection. ......