Intrauterine exposure to halothane increases murine postnatal autotolerance to halothane and reduces brain weight

The effect of halothane on prenatal development was assessed using the appearance of postnatal tolerance to the anesthetic and its effect on brain weight. Eighteen 3-month-old mice were repeatedly tested in a rotating cage for loss of righting reflex during exposure to increasing concentrations of halothane on 15 occasions to determine whether or not tolerance to halothane developed. Of these, nine mice were born to dams exposed for 30 min to 2% halothane on days 14 and 17 of gestation. The other nine mice (controls) were born to dams exposed to 100% oxygen for 30 min at the same stage of pregnancy. There was no significant difference in tolerance to halothane between the groups during the first nine days of repeated exposure to halothane. By the 13th and 15th days, however, mice exposed to halothane in utero became more tolerant to 1% halothane than did controls (P less than 0.025). In addition, the mean total brain weight of six 7-week-old mice exposed to 2% halothane in utero for 30 min on days 14 and 17 of gestation was found to be significantly less than the mean total brain weight of six control mice not exposed to halothane in utero (20.83 +/- 0.27 g and 23.07 +/- 0.51 g, respectively, P less than 0.0025). This difference occurred mainly in the brain stem rather than in the forebrain and cerebellum.