EFFECT OF PULSATILE OXYTOCIN ADMINISTRATION TO THE PREGNANT EWE IN THE LAST 3RD OF GESTATION ON FETAL ACTH AND CORTISOL RESPONSE TO ACUTE HYPOXEMIA

OBJECTIVE: The aim of this study was to examine the effect of increase d myometrial contractility throughout the last third of pregnancy on t he ovine fetal response to short-term hypoxemia. METHODS: Oxytocin (60 0 mu U/kg/minute, n = 5) or saline (n = 7) was infused for 5 minutes e very 20 minutes into the maternal jugular vein starting at 95-99 days of gestation and continuing throughout the last third of gestation. Fe tuses were subjected to a hypoxemic challenge (1 hour) at 131 days of gestation while fetal plasma ACTH and cortisol levels and nuchal muscl e electromyogram activity were monitored. RESULTS: The fetal plasma AC TH concentration before and during the hypoxemic challenge was similar in the control and oxytocin groups. The fetal plasma cortisol concent ration in the oxytocin group was significantly lower before and during the hypoxemia than in the controls. During hypoxemia, fetal nuchal mu scle activity was significantly reduced only in the control group. CON CLUSION: Increased myometrial contracture frequency throughout the las t third of pregnancy alters both the neuroendocrine and behavioral res ponses of fetal sheep to short-term hyperemia.