Effect of ondansetron on hypnotic and analgesic actions of isoflurane

OBJECTIVE To investigate the effect of ondansetron on hypnotic and analgesic effects of isoflurane and to explore their relationships with 5-HT3 receptors.METHODS ① Hypnosis experiment: Mice were ip given normal saline(NS) or ondansetron 1,2,4 mg·kg-1.15 min later,mice were also ip isoflurane 1.0 ml·kg-1 to get hypnotized and sleeping time was observed.② Hypnotic ED50 determination: Mice were ip given NS or ondansetron 2 mg·kg-1,15 min later,hypnotic ED50 of isoflurane was measured by sequential method.③ Writhing test: mice were divided into 8 groups,normal control,ondansetron 1,2,4 mg·kg-1,NS+isoflurane,ondansetron 1,2,4 mg·kg-1+isoflurane.Isoflurane 1.0 ml·kg-1 was sc given.The writhing times were observed.④ Hot-plate test: Mice were grouped as writhing test.Isoflurane 0.4 ml·kg-1 was ip given.The pain threshold in hot-plate pain test(HPPT) was observed.RESULTS Compared with normal control group,ondansetron had no significant effect on sleeping time in mice treated with isoflurane.There was no significant difference between ondansetron alone group and ondansetron+isoflurane group on ED50.Ondansetron 4 mg·kg-1 and isoflurane 1.0 ml·kg-1 could reduce writhing times(P0.01).Compared with isoflurane group,the writhing times of ondansetron+isoflurane groups were slightly reduced,but were not significantly different.In hot-plate test,ondansetron did not affect the HPPT in conscious mice or those treated with isoflurane.CONCLUSION Ondansetron doesn′t affect the hypnotic or analgesic effects of isoflurane.Hypnotic and analgesic effects of isoflurane have no obvious relationship with 5-HT3 receptor.