Antenatal betamethasone administration decreases the lung hyaluronan concentration in preterm rabbit pups

Maternal treatment with corticosteroids before preterm delivery is effectiv e in reducing the: incidence of respiratory distress syndrome and neonatal mortality. We hypothesized that corticosteroids might lower the lung hyalur onan concentration. Twenty-five rabbit dams (term = 31 d) with timed pregna ncies were injected s.c. with 0.75 mg of betamethasone or saline (controls) 1 d before delivery. In addition, two darns delivered at 25 d of gestation were injected with 0.75 mg of betamethasone on two consecutive days before delivery. A total of 238 live pups were delivered by preterm cesarean sect ion at 25, 27, 28, or 29 d of gestation and killed immediately. Their lung hyaluronan concentrations were measured with a radiometric assay, and wet/d ry lung weight ratios were determined. Lungs of rabbit pups exposed antenat ally to betamethasone and delivered at 25 or 27 d of gestation, but not at 78 or 79 d, displayed signiticantly (p = 0.001 and p = 0.008, respectively) lower hyaluronan concentrations than control pups, accompanied by less int ense subepithelial staining for hyaluronan in alveolar walls. There was no significant difference in wet/dry lung weight ratio between pups exposed to one dose of betamethasone and controls. Antenatal corticosteroid exposure lowers the lung hyaluronan concentration in preterm rabbit pups delivered a t 25 or 27 d of gestation, but not in those delivered at 28 or 79 d.