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1 Brown University School of Medicine, Department of Pediatrics, Women and Infants' Hospital of Rhode Island, Providence, Rhode Island 02905; and 2 Department of Surgery, State University of New York at Stony Brook, Stony Brook, New York 11794-8191
We
showed that antenatal corticosteroids reduced blood-brain barrier
permeability in fetuses at 60 and 80%, but not 90% of gestation, and
decreased brain water content in fetuses. Our objective was to examine
the effects of postnatal corticosteroids on regional blood-brain
barrier permeability and brain water content in newborn lambs.
Three dexamethasone treatment groups were studied in 3- to
5-day-old lambs. A 0.01 mg/kg dose was selected to estimate the amount
of dexamethasone that might have reached fetuses via antenatal
treatment of ewes in our previous studies. The other doses (0.25 and
0.5 mg/kg) were chosen to approximate those used clinically to treat
infants with bronchopulmonary dysplasia. Lambs were randomly assigned
to receive four intramuscular injections of dexamethasone or placebo
given 12 h apart on days 3 and 4 of age.
Blood-brain barrier function was measured with the blood-to-brain transfer constant (Ki) to 
-aminoisobutyric
acid, brain plasma volume was measured with polyethylene glycol for the
calculation of Ki, and brain water was measured
by wet-to-dry tissue weights. Postnatal treatment with corticosteroids
did not reduce barrier permeability in newborn lambs. Brain blood
volume was higher in the 0.25 and 0.5 mg/kg dose dexamethasone groups
than in the placebo group. Brain water content did not differ among the
groups. We conclude that postnatal treatment with corticosteroids did
not reduce regional blood-brain barrier permeability or brain water content but increased the brain plasma volume in newborn lambs. These
findings are consistent with our previous work indicating that barrier
permeability is responsive to corticosteroids at 60 and 80% of
gestation and brain water regulation at 60% of gestation, but not in
near-term fetuses or newborn lambs.
-aminoisobutyric acid; plasma cortisol; postnatal sheep
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