Effect of Pulsatile Oxytocin Administration to the Pregnant Ewe in the Last Third of Gestation on Fetal ACTH and Cortisol Response to Acute Hypoxemia

Abstract

Objective: The aim of this study was to examine the effect of increased myometrial contractility throughout the last third of pregnancy on the ovine fetal response of short-term hypoxemia.

Methods: Oxytocin (600 μU/kg/minute, n = 5) or saline (n = 7) was infused for 5 minutes every 20 minutes into the maternal jugular vein starting at 95-99 days of gestation and continuing throughout the last third of gestation. Fetuses were subjected to a hypoxemic challenge (1 hour) at 131 days of gestation while fetal plasma ACTH and cortisol levels and nuchal muscle electromyogram activity were monitored.

Results: The fetal plasma ACTH concentration before and during the hypoxemic challenge was similar in the control and oxytocin groups. The fetal plasma cortisol concentration in the oxytocin group was significantly lower before and during the hypoxemia than in the controls. During hypoxemia, fetal nuchal muscle activity was significantly reduced only in the control group.

Conclusion: Increased myometrial contracture frequency throughout the last third of pregnancy alters both the neuroendocrine and behavioral responses of fetal sheep to short-term hypoxemia.