Exposure of rabbit fetal lung to glucocorticoids in vitro does not enhance transcription of the gene encoding pulmonary surfactant-associated protein-B (SP-B).

We have investigated the ontogeny and hormonal regulation of both synthesis rates and cellular accumulation of the mRNA for surfactant-associated protein B (SP-B) in rabbit fetal lung. The developmental pattern for SP-B mRNA synthesis increased as a function of gestational age and paralleled that for SP-B mRNA levels except on days 22-26 of gestation where relatively higher levels of gene transcription were observed. Time-course studies with explants from 26- and 30-day fetal lung maintained in culture revealed a gradual increase in mRNA levels and a much smaller increase in gene transcription relative to adult values. Within 48 h of exposure of 26-day explants to dexamethasone at 10(-8) M there was a rapid increase in SP-B mRNA levels to 7-fold adult levels. A similar overall although somewhat slower and attenuated pattern was observed with 30-day explants. Dexamethasone at 10(-8) M had no effect on SP-B gene transcription with explants of either gestational age. We conclude that the major effect of dexamethasone treatment in vitro on SP-B mRNA levels appears to be post-transcriptional and there are small but distinct differences in the effects of glucocorticoids on SP-B mRNA levels with explant cultures from early and late stages of fetal lung maturation.