Effects of narcotic drugs on fetal behavioral activity: acute methadone exposure.

The effects of acute methadone exposure on fetal behavioral activity were investigated in 10 unanesthetized fetal lamb preparations. Fetal behavioral activity was interpreted indirectly from the electrocorticogram (ECoG), electromyogram, electrooculogram, blood pressure, heart rate (FHR), and breathing movements (FBMs) of the fetus. Methadone infusion to the mother (5 micrograms/kg/min) resulted in a suppression of all synchronized ECoG activity, and an increase in FBM, FHR, eye movements, nuchal tone, and body movements. Similar effects were observed when 10% of the dose was given directly to the fetus. These results demonstrate that methadone acts directly om the fetus to suppress both quiet sleep and rapid eye movement sleep and results in a "hyperactive" state that has previously been shown to be associated with a 20% increase in fetal oxygen consumption.