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 5 minute interval during a 60 minute 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 Frey type 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 phase 2 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 dose dependently 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.