Effects of antenatal steroids on ischemic brain injury in near-term ovine fetuses

Abstract

Background: Hypoxia/ischemia in utero can result in brain damage to the fetus and newborn. Antenatal steroids are a routine part of the management of women who develop premature labor. Pretreatment of young postnatal rats with dexamethasone before hypoxic/ischemic insults has been reported to attenuate brain injury. However, the effects of antenatal steroids on ischemic brain injury in fetuses have not been investigated. Objective: We examined the effects of maternally administered antenatal corticosteroids on ischemic brain injury in near-term ovine fetuses. Methods: Chronically instrumented fetuses at 122 days of gestation were studied 12 h after the last of four 4 mg dexamethasone, or placebo injections were given over 48 h to the ewes. Groups were dexamethasone/ischemic, placebo/ischemic and sham-treated control. Fetuses were exposed to 30 min of carotid occlusion (ischemia) or no occlusion (control) and 72 h of reperfusion. Whole brain coronal sections stained with Luxol fast blue-hematoxylin-eosin were scored for white matter and cerebral cortical lesions. Both areas received pathological scores of 0 to 5 reflecting the degree of injury (0=0%, 1=1–10%, 2=11–50%, 3=51–90%, 4=91–99% and 5=100%). Bilateral carotid blood flow also was measured before, during and after brain ischemia in the dexamethasone/ischemic and placebo/ischemic groups. Results: White matter (WM) and cerebral cortical scores did not differ between the dexamethasone/ischemic and placebo/ischemic (WM: 3.0±1.9 and 2.9±1.7; cortex: 3.1±1.7 and 2.6±1.8, mean±S.D.) groups. White matter and cerebral cortical scores were higher in the dexamethasone/ischemic (WM: 3.0±1.9, P<0.02; cortex: 3.1±1.7, P<0.005) and placebo/ischemic (WM: 2.9±1.7, P<0.006; cortex: 2.6±1.8, P<0.007) than control (WM: 0.2±0.4; cortex: 0.2±0.4) group. Carotid blood flow was relatively higher ( P<0.05) after 24, 48 and 72 h of reperfusion in the dexamethasone/ischemic than placebo/ischemic group. Conclusions: We conclude that maternal pretreatment with antenatal dexamethasone did not attenuate ischemic brain injury in the fetus, and that carotid blood flow was higher during reperfusion in fetuses of dexamethasone than placebo-treated ewes, most likely secondary to decreases in arterial oxygen tension.