The rat testis and liver or human liver microsomes were used for 11β-HSD1 assay. 11β-HSD1 activity was performed in the microsome according to a previously described method  . In brief, the assay tubes contained 25 nM substrate 11DHC (for rat) or cortisone (for human), spiked with 30,000 cpm their respective 3 H-11keto-steroid, mM NADPH and 5 mM glucose-6-phosphaare in the PBS buffer. 2 µg microsomes were added to each tube to initiate the reaction and the reaction mixture was incubated for up to 2 hrs, during which the reaction is within the linear range. The rest procedure was similar to 11β-HSD1 assay in intact cells.
The two 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD) isozymes catalyze the interconversion of cortisol and cortisone. Type 1 11 beta-HSD (11 beta-HSD1) has bidirectional activity, while type 2 11 beta-HSD (11 beta-HSD2) mainly converts cortisol into cortisone. Of these two hormones only cortisol has affinity to mineralocorticoid receptors (MRs) and thus induces mineralocorticoid effects. A normal activity of 11 beta-HSD2 is crucial for prevention of mineralocorticoid activity of cortisol. Absent or decreased 11 beta-HSD2 activity results in cortisol-mediated hypermineralocorticoid hypertension. In several hypertensive syndromes a decreased 11 beta-HSD2 activity has been described as the pathogenetic mechanism of the increased blood pressure. In the apparent mineral corticoid excess (AME) syndrome type 1, absence of 11 beta-HSD2 activity is caused by mutations in the gene coding for 11 beta-HSD2. In licorice-induced hypertension glycyrrhetinic acid, the active substituent of licorice, inhibits 11 beta-HSD2 resulting in an acquired hypermineralocorticoid state. 11 beta-HSD2 activity is not decreased in glucocorticoid hypertension (Cushing's syndrome). In essential hypertension some evidence for decreased systemic and skin activity of 11 beta-HSD1 and/or 11 beta-HSD2 has been found, while renal activity of both isozymes appears to be normal. 11 beta-HSD2 activity is also present in cardiovascular myocytes of humans and dogs, and inhibition of 11 beta-HSD potentiates the vascular response to catecholamines. Although MRs in the central nervous system have been incriminated in the pathogenesis of mineralocorticoid hypertension, a pathophysiological role for 11 beta-HSD2 has not yet been described. Finally, in the placenta 11 beta-HSD2 reduces fetal exposure to maternal glucocorticoids and a decreased activity of this isozyme may result in low birth weight and increased risk of high blood pressure at adult age.