Pulsatile oxytocin administered to ewes at 120 to 140 days gestational age increases the rate of maturation of the fetal electrocorticogram and nuchal activity.

Abstract

Spontaneous, long lasting epochs of myometrial contractility, contractures, occur throughout the majority of pregnancy in sheep. Contractures are temporally related to a switch in fetal electroencephalogram (ECoG) patterns from low to high voltage. In late gestation, fetal ECoG increases in voltage. We have previously suggested that contractures may influence fetal ECoG maturation. In the present study, we hypothesized that a sustained increase in the frequency of myometrial contractures in pregnant sheep at 120-140 days gestation would accelerate maturation of the fetal ECoG. Five pregnant ewes were pulsed with oxytocin 600 microU.kg-1.min-1 intravenously for five minutes in every 30 minutes from 127.8 +/- 1.5 days gestational age for a minimum of six days. Six control ewes received pulses of saline. Fetuses of all eleven ewes were instrumented with bilateral electrodes to record fetal ECoG and nuchal muscle activity. Fetal high voltage (HV) ECoG increased in amplitude in both groups but the rate of increase was faster in the fetuses of ewes receiving oxytocin. There were no differences between the two groups in the duration of HV ECoG. The percentage increase in the amount of time the fetal nuchal muscles were active compared with the baseline day before infusion was only significant in the oxytocin infused group on the first day of oxytocin infusion. These findings support the hypothesis that myometrial activity during pregnancy has the capacity to influence fetal neural development.