Corticosterone and 11-dehydrocorticosterone stimulate Na,K-ATPase gene expression in vascular smooth muscle cells.

BACKGROUND

In mineralocorticoid target tissues such as kidney and colon, the enzyme 11 beta-hydroxysteroid dehydrogenase (11 beta OHSD) catalizes the reversible conversion of corticosterone (CS) to inactive 11-dehydrocorticosterone (DHCS) in rats, and cortisol to inactive cortisone in humans. This enzyme is also expressed in vascular smooth muscle cells (VSMC).

METHODS

In cultured VSMC from rat thoracic aortae, we examined the effects of CS and DHCS on Na,K-ATPase alpha 1- and beta 1-mRNA accumulation by Northern blot analysis, on alpha 1- and beta 1-subunit protein accumulation by Western blot analysis, and on Na,K-ATPase activity by the coupled assay method.

RESULTS

In VSMC, CS and DHCS (10(-6) M) increased alpha 1-mRNA level 2.6- and 2.5-fold at 48 hours and beta 1-mRNA level 9.2- and 9.1-fold at 12 hours, respectively. The RNA transcription inhibitor (actinomycin D) abolished both CS- and DHCS-mediated alpha 1- and beta 1-mRNA induction. The glucocorticoid receptor antagonist (RU38486) and the mineralocorticoid receptor antagonists (ZK91587) inhibited both CS- and DHCS-mediated alpha 1- and beta 1-mRNA induction. The 11 beta OHSD inhibitor (carbenoxolone) inhibited DHCS-mediated alpha 1- and beta 1-mRNA induction, whereas it caused no effect on CS-mediated alpha 1- or beta 1-mRNA induction. The addition of CS or DHCS to VSMC significantly increased alpha 1- and beta 1-subunit protein levels and Na,K-ATPase activity. When adrenalectomized rats were treated with CS or DHCS for 12 hours, aorta alpha 1- and beta 1-mRNA levels increased 3.0- and 8.7-fold or 3.4- and 8.4-fold, respectively.

CONCLUSIONS

In VSMC, both CS and DHCS stimulate Na,K-ATPase alpha 1- and beta 1-mRNA accumulation, alpha 1- and beta 1-subunit protein accumulation, and Na,K-ATPase activity. The CS-mediated alpha 1- and beta 1-mRNA induction occurs independently of 11 beta OHSD, whereas the DHCS-mediated alpha 1- and beta 1-mRNA induction occurs through 11 beta OHSD-dependent mechanisms, possibly via conversion of inactive DHCS into active CS.