19-hydroxyandrostenedione does not modulate [3H]aldosterone binding to human mononuclear leucocytes and rat renal cytosol.

Abstract To verify the aldosterone amplifying action of 19-hydroxyandrostenedione (19-OH-AD), we investigated [ 3 H]aldosterone and [ 3 H]19-OH-AD binding to type I (mineralocorticoid) receptor in the renal cytosol of adrenalectomized and ovariectomized rat, and human mononuclear leucocytes (MNL). In the [ 3 H]aldosterone binding study, the cytosol was incubated with [ 3 H]aldosterone and 200-fold RU28362 (11β,17β-dihydroxy-6-methyl-,17α-(1-propynyl)-androsta-1,4,6,-trien-3-one), a pure glucocorticoid, with or without 19-OH-AD. Scatchard plots of [ 3 H]aldosterone binding to cytosol with 0.2 or 20 nM 19-OH-AD or without 19-OH-AD were linear. Dissociation constants ( K d ) and maximum bindings (B max ) without 19-OH-AD, and with 0.2 and 20 nM 19-OH-AD were: 0.71 ± 0.03 nM and 23.0 ± 3.4 fmol/mg protein (mean ± SD, n = 3), 0.72 ± 0.05 nM and 23.1 ± 2.3 fmol/mg protein ( n = 3), and 0.77 ± 0.04 nM and 22.9 ± 4.8 fmol/mg protein ( n = 3), respectively. 19-OH-AD did not significantly change the K d and B max of [ 3 H]aldosterone binding. A high concentration of 19-OH-AD slightly displaced 0.2 or 5 nM [ 3 H]aldosterone bound to cytosol. In human MNL, Scatchard plots of [ 3 H]aldosterone binding with both 0.2 and 20 nM 19-OH-AD and without 19-OH-AD were linear. K d and B max were, respectively, 1.00 nM and 780 sites/cell in the absence of 19-OH-AD, and 1.07 nM and 774 sites/cell in the presence of 0.2 nM 19-OH-AD. Without 19-OH-AD they were, respectively, 0.95 nM and 551 sites/cell, and 1.10 nM and 560 sites/cell with 20 nM 19-OH-AD. A high concentration of 19-OH-AD slighly displaced 0.2 or 5 nM of [ 3 H]aldosterone bound to MNL. In both tissues, there was no obvious specific binding of [ 3 H]19-OH-AD within the range of 1–60 nM. The above results suggest that the amplifying effect of 19-OH-AD on aldosterone mineralocorticoid action may not occur at the binding site of aldosterone to type I receptor, and that 19-OH-AF itself may not have any direct or indirect mineralocorticoid actions on the steroid receptor-mediated process in the rat kidney and human MNL.