Tissue specific effects of thyroid hormone on 11 beta-hydroxysteroid dehydrogenase gene expression

11 beta-Hydroxysteroid dehydrogenase (11 beta-HSD) by converting active glucocorticoid to an inactive metabolite confers specificity upon the mineralocorticoid receptor (MR) and regulates ligand access to the glucocorticoid receptor (GR). Factors which influence 11 beta-HSD activity seem likely to be of considerable importance in the modulation of both mineralocorticoid and glucocorticoid hormone action. The administration of tri-iodothyronine (T3) to rats has previously been shown to reduce 11 beta-HSD activity in liver but not in kidney. We have studied the effect of T3 on 11 beta-HSD gene expression in vivo in rat liver, kidney, distal colon and pituitary. In addition the effects of T3 on 11 beta-HSD gene expression in vitro in the rat pituitary GH3 cell line have been studied. T3 administration to normal adult rats (40 micrograms/day, s.c. for 1, 3 and 7 days) resulted in a marked decline in liver and pituitary 11 beta-HSD mRNA levels and activity following 3 and 7 days of treatment. These reduced levels were maintained for 3 days following withdrawal of T3 treatment, but returned to control levels after 7 days. In contrast 11 beta-HSD mRNA and activity in kidney and distal colon were unaffected by T3 treatment at each time point studied. In vitro, levels of 11 beta-HSD mRNA and activity in GH3 cells were unchanged following 8, 24 and 72 h treatment with T3 (10(-8) to 10(-6) M). T3 bio-activity was confirmed by a marked dose-dependent decline in the expression of the T3 and glucocorticoid responsive gene, prolactin. T3 inhibits 11 beta-HSD gene expression in both liver and pituitary at a pre-translational level. This effect is absent in the predominantly mineralocorticoid target tissues, kidney and distal colon, i.e. it is tissue specific and as such is consistent with the existence of multiple differentially regulated isoforms of 11 beta-HSD. The time course of the T3 effect in liver and pituitary in vivo and the lack of any effect in vitro suggests that this action is indirect, and not as a result of interaction between the T3 receptor and the putative thyroid hormone response element on the rat 11 beta-HSD gene.