Abstract
The influence of adenosine on the antinociceptive effect for nitrous oxide, and morphine was studied by using the tail-flick test in rat. Under spontaneous breathing by 75% nitrous oxide and/or 75% nitrogen, analgesic effects were examined in 6 groups ; 75% nitrous oxide only inhalation group, nitrous oxide with aminophylline group, nitrous oxide with naloxone group, morphine group, morphine with aminophylline group, morphine with naloxone group. We determined that intrathecal adenosine A1 agonist (R-PIA) increased analgesic effect, but intrathecal aminophylline suppressed these analgesic effect. Seventy-five percent nitrous oxide inhalation increased analgesic effect by 75% (%MPE) at 30 minutes, and these analgesic effect could not suppress by using with intrathecal aminophylline or intravenous naloxone. Intrathecal morphine increased analgesic effect by 84% (%MPE) at 15 minutes point, but these analgesic effects were suppressed by using intrathecal aminophylline or intravenous naloxone. These results support that analgesic effects of nitrous oxide did not participated in opioid action or adenosine agonist at spinal cord, and the analgesic effects of morphine participated in opioid action or adenosine agonist at spinal cord.
