Journal of Applied Physiology, Vol 68, Issue 3 1134-1141, Copyright © 1990 by American Physiological Society
Antenatal betamethasone dose effects in preterm rabbits studied at 27 days gestation
E. D. Rider, A. H. Jobe, M. Ikegami, T. Yamada and S. Seidner
Department of Pediatrics, Harbor-UCLA Medical Center, Torrance 90509.
Pregnant rabbits received bethamethasone (0.05, 0.2, 0.4, or 0.5
mg.kg-1.day-1) or vehicle control for 2 days before delivery of fetuses at
27 days gestation to evaluate dose-related effects on surfactant pool sizes
with and without ventilation, pressure-volume measurements, lung protein
leaks, and precursor incorporation into lung saturated phosphatidylcholine
(PC). Alveolar wash-saturated PC pool sizes in betamethasone-exposed
fetuses were less than in controls (P less than 0.01). At higher doses,
total lung saturated PC also decreased (P less than 0.01). Maximal lung
volumes on pressure-volume loops were larger than controls only at the 0.4
mg.kg-1.day-1 dose (P less than 0.05). The larger maximal volumes, despite
decreased saturated PC pools, indicated increased responsiveness of the
steroid-treated lungs to the smaller saturated PC pool sizes.
Vascular-to-alveolar iodinated albumin leak decreased with steroid
treatment independently of dose (P less than 0.01). No consistent pattern
of increased precursor incorporation into saturated PC by lung slices was
seen. Our results indicate that, in preterm rabbits exposed to a range of
maternal corticosteroid doses, the beneficial lung maturational effect of
structural alterations with increased responses to endogenous saturated PC
pools was maximal even at the lowest dose.
