Dexamethasone enhances surfactant protein gene expression in streptozotocin-induced immature rat lungs

Because surfactant protein (SP) mRNA levels in rat fetuses are increased by maternal dexamethasone (dex) treatment and decreased in streptozotocin-induced diabetic (STZ-DB) pregnancy, we investigated the in vivo effects of dex on SP gene expression in STZ-DB pregnancy. The mRNA levels of SP (SP-A, SP-B, SP-C) were assessed in d 18 and 20 fetuses by Northern blot analysis, and nuclear run-on assays were performed with lung nuclei from d 20 fetuses (term = 22 d). Our findings indicate: 1) dex causes a greater increase in SP-A and SP-B mRNA levels in d 18 (12-16-fold) compared with day 20 (4-6-fold) fetuses (p < 0.05) in normal and STZ-DB pregnancy; 2) a 2-3-fold increase in SP-C mRNA levels was observed in response to dex in d 18 and 20 fetuses; 3) the increase in transcription of SP-A and SP-B in d 20 fetuses after dex is 68 and 60%, respectively, of the increase in their mRNA levels whereas in STZ-DB, the decrease in transcription compared with mRNA levels is 3.67-fold for SP-A and 2.42 fold SP-B; and 4) changes in SP-C transcription in either in vivo model, dex-treated or STZ-DB, correspond well with changes in mRNA levels. Together, these findings indicate that dex can enhance SP expression in STZ-DB immature lungs and support differential regulation of fetal SP genes in the models studied.