EFFECT OF PULSATILE INTRAVENOUS OXYTOCIN ADMINISTRATION TO PREGNANT SHEEP OVER THE LAST 3RD OF GESTATION ON FETAL ACTH AND CORTISOL RESPONSES TO HYPOTENSION

OBJECTIVE: To examine the effect of increasing myometrial contractilit y in the last third of gestation on ovine fetal response to hypotensio n. METHODS: Oxytocin (600 mu U/kg/minute) or saline was infused via th e maternal jugular vein as 5-minute pulses every 20 n minutes, startin g at 97 +/- 1 days of gestational age (mean +/- standard error of the mean) until labor. Fetal hypotension (10 minutes) was induced by intra venous nitroprusside infusion at 133 +/- 1 days' gestation. RESULTS: E wes from both groups went into labor at the same gestational age. Tota l fetal body and adrenal gland weights were higher in controls than in the oxytocin-treated group. Maternal arterial pH and blood gas values were normal throughout the study. At 132-136 days' gestation, fetal a rterial oxygen pressure was lower in the oxytocin group than in contro ls (P <.05). Basal fetal ACTH concentrations did not change between 13 0 and 136 days in both groups. The mean fetal plasma ACTH concentratio n was not different between the control (40.6 +/- 4.1 pg/mL) and oh yt ocin groups (32.6 +/- 4.9 pg/mL). Pre-hypotension fetal plasma ACTH wa s similar in both groups, whereas cortisol was lower in the oxytocin g roup. Hypotension significantly increased fetal plasma ACTH and cortis ol concentrations; however, both ACTH and cortisol responses were smal ler in the oxytocin group (P <.05). CONCLUSIONS: Increased myometrial contractility throughout the last third of gestation modifies the norm al ACTH nd cortisol relation at the critical time of prepartum increas e in adrenocortical activity. In addition, fetal ACTH and cortisol res ponses to hypotension ave diminished in fetuses exposed to such a prol onged increase in myometrial contractility. These observations support the hypothesis that myometrial contractility influences fetal neuroen docrine development.