Effect of propofol on perception of pain in mice: mechanisms of action

The latencies of pain threshold to different subhypnotic doses (12.5, 25 and 50 mg kg(-1)) of propofol, an anaesthetic, administered intraperitoneally (i.p.) into male mice were measured using a hot plate method. The possible mechanism of pain control by propofol was also investigated through blocking beta-endorphin receptors and measuring serum level of beta-endorphin. Morphine (1.5 mg kg(-1) i.p.) was used as a reference of reduction of pain sensation. The results showed that propofol in doses of 25 and 50 mg kg(-1) significantly (P < 0.01) increased the latency of pain threshold but a lower dose (12.5 mg kg(-1)) failed to produce any significant change. This indicates that propofol reduced pain and this effect is dose-dependent. Propofol prevents hyperalgesia produced by prostaglandin PGE(2), (0.5 mg kg(-1), i.p.; P < 0.01). Pretreatment with naloxone (1.0 mg kg(-1), i.p.) abolished significantly (P < 0.01) the antinociceptive action of propofol. Furthermore, serum level of beta-endorphin was increased (P < 0.01) after propofol injection particularly at the peak time of propofol action. The serum level of corticosterone was also increased (P < 0.01) at the time of beta-endorphin release. It was concluded that propofol can control pain and this action may be centrally modulated through the opioid system rather than at the level of the spinal cord. (C) 1998 Elsevier Science Inc. All rights reserved.