The Analgesic Mechanism Of Propofol On Visceral Nociception In Spinal Cord In Rat

[Objective] To investigate the interaction of antinociceptive mechanism of propofol on visceral nociception with opioid receptors and a 2-adrenoceptors at the level of the spinal cord.[Method] 1, Behavioral responses: After intrathecal catheter being implanted,91 adult male SD rats weighting 180-260g were randomly divided into 13 groups of seven each.The animals were pretreated with normal saline or different drug intrathecally and intraperitoneally.Then using colorectal distension (CRD) model as a visceral pain model, the minimal pressure that causes rat abdomen flatting was considered as a visceromotor threshold (VMT) and the baseline and postdrug VMTs were determined respectively before and after administration. 2, Morphologic method: 48 adult male SD rats weighting 180-260g were randomly divided into 10 groups. Except one control group,each animal was treated with normal saline or drug intrathecally and intraperitoneally and was given a noxious colorectal distension stimulus (80mmHg,20min).Then each lumbosacral spinal cord segment (L6-Sl)was removed for immunohistochemistry and the number of FLIN was counted.[Results] 1, In the behavioral responses detection,VMR thresholds during 5-25 min significantly increased after intraperitoneal injection of 10 mg/kg propofol(p<0.01).The peak effect was observed at 10 min with a maximal MPE 37.2%. Only pretreatment with naloxone did not change VMR thresholds significantly(p>0.05). The visceral antinociceptive effect of propofol which had appeared was reversed at different degree by intrathecal pretreatment with naloxone or/and yohimbine . furthermore, the reverse effect of intrathecal injecting naloxone and yohimbine simultaneously was markedly greater than pretreatment with naloxone or yohimbine alone. 2, In the morphologic results,there was a significant increase in the number of FILN in several laminae and overall section of L6-S1after rats were given noxious colorectal distension stimuli.A great reduction was observed when propofol lOOmg/kg was administered intraperitoneally. Naloxone or/and yohimbine pretreatment intrathecally partially reversed the effect of propofol. The reverse effect of intrathecal injecting naloxone and yohimbine simultaneously was in a synergistic manner.[ Conclusions ] (1) Propofol has antinociceptive effect on visceral nociception induced by CRD. (2) The visceral antinociceptive mechanism of propofol may be in relation to opioid receptor at spinal level. (3) The visceral antinociceptive mechanism of propofol may be in relation to a 2-ardenoceptor at spinal level. (4) Spinal opioid receptor and a 2-ardenoceptor participate synergistically in the visceral antinociceptive mechanism of propofol.