Background: Antenatal treatment with corticosteroids before preterm delivery is effective in reducing the incidence of respiratory distress syndrome (RDS). We hypothesize that some of the corticosteroid effects on lung function and/or lungwater might be mediated through changes in the lung hyaluronan (HA) content.

Methods: Rabbit dams with timed pregnancies were injected one day before delivery with 0.75 mg betamethasone in saline or saline only(controls). Pups were delivered at 27 days of gestation by cesarian section, and killed immedeately. The trachea was tied and lungs removed en bloc. Wet/dry lung weight ratio (W/D) and HA concentration were determined using freeze-drying and Pharmacia's HA kit.

Results: Control pups (n=23) had a mean (± SEM) HA concentration of 494.2 ± 25.4 μg/g dry lung weight, and a W/D of 9.1± 0.1. Pups of dams antenatally treated with betamethasone (p=29) showed a significantly lower (p=0.006) HA concentration of 382.4 ± 17.3μg/g dry lung weight than controls, and an almost equal W/D ratio of 9.3 + 0.6.

Conclusion: Preterm rabbit pups of dams given 1 antenatal dose of corticosteroids have lower lung HA than control pups, while W/D is equal in both groups.