ONTOGENY AND EFFECTS OF EXOGENOUS SURFACTANT TREATMENT ON SP-A, SP-B, AND SP-C MESSENGER-RNA EXPRESSION IN RABBIT LUNGS

The aims of the present study were to first characterize the ontogeny of mRNAs encoding the principal surfactant proteins SP-A, SP-B, and SP-C in rabbit lung tissues, followed by an evaluation of the effect of exogenous surfactant administration on endogenous expression of mRNA levels. Lung tissues were collected from New Zealand White rabbits on days 19, 21, 24, 26, 28, 30 of gestation, 1 day and 10 days after birth, and as adults. SP-A, SP-B, and SP-C mRNAs were first detected on gestational days 26, 24, and 19, respectively. The specific levels of these mRNAs generally increased to gestational day 28 and decreased transiently on 1 day of life. Adult values remained lower than those noted at 30 days gestation. For the second study, 29-day-gestation preterm rabbits were given either one or two treatment doses of natural surfactant or an organic solvent extract of natural surfactant, and mRNA levels were measured 10 or 24 h later. No effect of surfactant treatments, type of surfactant, or dosage (1 or 2 treatments) was noted on SP-A, SP-B, or SP-C mRNA expression. These data indicate that the mRNA expression for the three major surfactant proteins was highest late in gestation in developing rabbits and that exogenous surfactant treatment was not associated with significant changes in SP-A, SP-B, or SP-C mRNA levels.