Antenatal steroids decrease blood-brain barrier permeability in the ovine fetus

Antenatal corticosteroid therapy reduces the incidence of intraventricular hemorrhage in premature infants. Enhanced microvascular integrity might pro vide protection against intraventricular hemorrhage. In the adult, there is evidence to suggest that the blood-brain barrier may be under hormonal con trol. We hypothesized that antenatal corticosteroids decrease blood-brain b arrier permeability in the preterm ovine fetus. Chronically instrumented 12 0-day-gestation fetuses were studied 12 h after the last of four 6-mg dexam ethasone (n = 5) or placebo (n = 6) injections had been given over 48 h to the ewes. Blood-brain barrier function was quantified with the blood-to-bra in transfer constant (K-i) for a-aminoisobutyric acid (AIB). K-i was signif icantly lower across brain regions in the fetuses of ewes that received ant enatal dexamethasone compared with placebo (ANOVA; interaction, F = 2.54, P < 0.004). In fetuses of dexamethasone- and placebo-treated ewes, K-i (mu l . g brain wt(-1) . min(-1), mean +/- SD) was, respectively, 2.43 +/- 0.27 vs. 3.41 +/- 0.74 in the cortex, 4.46 +/- 0.49 vs. 5.29 +/- 0.85 in the cer ebellum, and 3.70 +/- 0.49 vs. 5.11 +/- 0.70 in the medulla. We conclude th at antenatal treatment with corticosteroids reduces blood-brain permeabilit y in the ovine fetus.