In adult mammals, liver and kidney are the two major sites of biosynthesis for 11β-hydroxysteroid dehydrogenase (11β-HSD) 1 and 2 respectively. In the present study, the expression of these two isozymes in the developing ovine fetal liver and kidney was characterized. Livers and kidneys were obtained from fetal sheep at days 85, 100–120 and 140–143 of gestation (term=145 days). Tissue levels of 11β-HSD2 mRNA were assessed by Northern blot analysis. 11β-HSD dehydrogenase and reductase activities in tissue homogenates were determined by a radiometric conversion assay using cortisol and cortisone as physiological substrates respectively. The unidirectional 11β-HSD2 dehydrogenase activity was identified by its distinct co-factor preference (NAD), and by its unique ability to metabolize dexamethasone (Dex). In the liver, 11β-HSD1 dehydrogenase and reductase activities were present by day 85, and their levels did not change between days 85 and 100–120 but increased more than twofold at days 140–143. This was consistent with changes we reported previously in the fetal hepatic 11β-HSD1 mRNA. 11β-HSD1 reductase activity was always higher than the dehydrogenase activity. 11β-HSD2 mRNA and activity were undetectable in the fetal liver at all three ages. By contrast, 11β-HSD2 mRNA was present in the fetal kidney by day 85, and its abundance increased progressively thereafter. There was a parallel increase in the renal 11β-HSD2 activity. Dex was also converted to 11-dehydro-Dex by the fetal kidney. In keeping with the absence of the full-length 11β-HSD1 mRNA, 11β-HSD1 activity was undetectable in the kidney. These results indicate that (1) 11β-HSD1 and 2 genes are differentially expressed and regulated in the fetal liver and kidney during development, (2) since the hepatic 11β-HSD1 reductase activity is always higher than the dehydrogenase activity, the fetal liver may be a potential extra-adrenal source of cortisol, and (3) 11β-HSD2 in the kidney may play a very important role in protecting the fetus from elevated levels of bioactive glucocorticoids.
Journal of Endocrinology (1995) 147, 405–411