Abstract 2051 Poster Session II, Sunday, 5/2 (poster 240)

Antenatal steroids are given to enhance pulmonary maturity. They also exert a wide range of extrapulmonary effects including a reduction in the incidence of intraventricular hemorrhage. Effects of perinatal steroids on the developing brain have not been well documented. We have recently shown that antenatal steroids decrease the blood-brain barrier permeability in ovine fetuses at 80% gestation. Little information is available regarding other effects of steroids on the developing cerebrovasculature. Some studies have examined the effect of steroids on the vascularity of tumurous brain tissue in animal models and shown a decrease in the vessel volume of brain tumors with no decrease observed in normal brain tissue (Nakagawa, et al., J Neurooncol, 6(2):157-68, 1988). We examined the effect postnatal steroids on regional brain blood volume measured with polyethylene glycol (MW 4000) in 5 day old newborn lambs. A placebo and two dexamethasone (DEX) injected groups were studied. DEX was given as a low dose (LD), 0.01 mg/kg/dose, selected to mimic the estimated fetal dose received during antenatal maternal treatment (Stonestreet, et al., Am J Physiol, 1998, in press; Sysyn, et al., Pediatr Res, 43, 197A, 1998); or a high dose (HD), 0.5 mg/kg/dose, chosen to simulate doses used to attenuate the development of bronchopulmonary dysplasia in mechanically ventilated premature infants. Lambs were instrumented on day 2 of life and allowed to recover. On days 3-4 of life, four consecutive intramuscular doses were given every 12 hours for 48 hours. Regional vascular volume measurements were made 12-15 hrs after the final dose. Values are summarized in the Table (Mean, range). The HD group had higher brain blood volume values than that of the placebo group (*ANOVA, F=13.65, p<0.05). There were no differences (F=4.80, p=0.09) in vascular volumes among the LD and control, or the LD and HD (F=6.21, p=0.07) groups. We conclude that high dose postnatal steroids increase regional brain vascular volume. These findings differ from the effects of DEX on tumorous adult brain tissue. Our findings may reflect a steroid mediated change in localized vessel surface area and/or vessel volume.

Table 1 No caption available
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(Supported by NIH-HD34618)