Magnesium Sulfate and Fetal Plasma Concentrations of Epinephrine, Norepinephrine, and Vasopressin in Response to Acute Hypoxemia in Goats

Abstract

We measured fetal plasma concentrations of epinephrine, norepinephrine, and vasopressin during acute hypoxemia in goats and tested whether hypermagnesemia altered these endocrine responses. Five chronically catheterized goat fetuses at 124-129 days' gestation were used. After 4 hours of infusion (magnesium or vehicle as controls), 30 minutes of hypoxemia was induced by infusing nitrogen gas through a maternal tracheal catheter. Fetal plasma concentrations of epinephrine, norepinephrine, and vasopressin were measured before and during hypoxemia. Both magnesium sulfate and vehicle infusions were performed in each animal. Repeated-measures analysis of variance (ANOVA) and two-way ANOVA with post hoc test were used to determine statistical significance. During hypoxemia, fetal PO(2) decreased significantly from 30 to 14 mmHg with no significant changes in fetal pH or PCO(2) in both groups. Fetal heart rate was reduced significantly by hypoxemia, but to a lesser extent in the magnesium group (change in decrease in fetal heart rate: 41 beats per minute [bpm] in controls versus 26 bpm with magnesium). Mean blood pressure did not change significantly during hypoxemia in both groups. Fetal plasma concentrations of epinephrine, norepinephrine, and vasopressin significantly increased from the prehypoxemic values both with magnesium and in controls. There were no significant differences in these hormone concentrations between magnesium and the controls. Magnesium sulfate had no effect on fetal plasma concentrations of vasopressin, epinephrine, and norepinephrine during acute hypoxemia.