BOLD-MRI demonstrates acute placental and fetal organ hypoperfusion with fetal brain sparing in response to phenylephrine but not ephedrine

Introduction: We previously reported blood oxygen level dependent MRI (BOLD-MRI) for monitoring placental and fetal hemodynamic changes in mice following maternal hypercapnia. Here we use BOLD-MRI to compare the placental and fetal hemodynamic effects of different maternal vasopressors in mice. Methods: Pregnant ICR mice (n = 16; E17.5) anesthetized with pentobarbital (80 mg/kg i.p.) were placed supine in a 4.7-T Bruker Biospec MRI. Following baseline images, equipotential doses of ephedrine (10 mg/kg) or phenylephrine (10mcg/kg) were administered intravenously. Changes in placental and fetal signal were analyzed from T2*-weighted gradient echo MR images (TR/TE = 147/10 ms). Different regions of interest (placenta, fetal heart, fetal liver and fetal brain) were identified. Percentage change of BOLD-MRI signal intensity (SI) were presented as time curves. Results: Ephedrine and phenylephrine elicited markedly different effects. Phenylephrine caused an approximate 50% reduction in placental, fetal heart and fetal liver BOLD-MRI-SI, but fetal brain BOLD-MRI-SI was unchanged (statistically different from placenta and other fetal organs; p < 0.001), and the fetal brain/liver BOLD-MRI-SI ratio was markedly increased versus baseline (p < 0.001). Following ephedrine, placental BOLD-MRI-SI increased 30% and fetal heart BOLD-MRI-SI was reduced 26%; other fetal organs were unchanged. Blood gases were unchanged. Discussion: Phenylephrine induced BOLD-MRI-SI changes suggestive of placental and fetal hypoperfusion with brain sparing. Ephedrine induced BOLD-MRI-SI changes suggestive of increased cardiac output; we speculate that reduced fetal heart BOLD-MRI-SI may be due to increased fetal myocardial oxygen extraction or metabolic acidosis. The result demonstrates the potential of BOLD-MRI as a non-invasive hemodynamic tool for assessing pharmacodynamics effects in the placental and fetus.