A NONISOTOPIC METHOD FOR ESTIMATING 11-BETA HYDROXYSTEROID DEHYDROGENASE-ACTIVITY IN-VIVO

11 beta-hydroxysteroid dehydrogenase (11 beta HSD) has both dehydrogen ase (11 beta DH) and reductase (11 beta R) activities, which catalyse the interconversion of cortisol and cortisone, and prednisolone and pr ednisone. This enzyme confers specificity on the mineralocorticoid rec eptor by local oxidation of cortisol to cortisone. Using radiolabelled cortisol 11 beta HSD activity has been shown to be lower in some case s of essential hypertension. This study investigated a novel approach to estimating 11 beta HSD activity in vivo. Plasma steroid kinetics we re investigated following oral hydrocortisone (a substrate for 11 beta DH) and prednisone (a substrate for 11 beta R) in five normotensive v olunteers after dexamethasone suppression of endogenous steroid produc tion. This approach was evaluated by inducing partial deficiency of 11 beta HSD in the volunteers who took liquorice (to inhibit 11 beta DH) and then carbenoxolone (to inhibit both 11 beta DH and 11 beta R). Th e ratio of cortisol to prednisolone (formed from prednisone) provided a measure of the activity of both 11 beta DH and 11 beta R. At 75 min after the steroid bolus the ratio increased from 1.1 (0.6-1.3) (median , range) under control conditions to 1.2 (0.8-1.7) after liquorice (P= 0.01, n = 5), and 2.0 (1.3-5.9) after carbenoxolone (P=0.02, n= 5). It may therefore be applied to the measurement of 11 beta HSD activity i n vivo in large numbers of hypertensive patients without the use of ra dioisotopes.