Autoradiographic study of aldosterone and dexamethasone binding in isolated glomeruli of rabbit kidney

Specific binding of tritiated aldosterone ([3H]A) and dexamethasone ([3H]Dex) has been investigated in glomeruli isolated from rabbit kidney by microdissection, using an autoradiographic method on dry film. At low physiological concentrations of [3H]A (0.2-2 nM), no specific binding was detected. At high concentration (24 nM), a low specific binding was found in cytoplasm (2.5 specific silver grains/100 micrometers2) and nuclei (3.7), which was about 10 times lower than in distal tubule. No difference was found between superficial and juxtamedullary glomeruli. At 2.4 nM [3H]A, no aldosterone binding was present in glomerular arterioles. Nuclear binding of [3H]Dex was low at 3 nM (6.4 specific silver grains/100 micrometers2) and reached 23.6 at 100 nM without significant cytoplasmic binding. Here again, this binding was much lower than in distal structures of the nephron. In the few arterioles obtained, a clear specific nuclear binding was observed. We conclude that the glomerulus is probably not a target structure for aldosterone. The existence of a specific binding of dexamethasone, although lower than in the distal tubule, raises the problem of its physiologic significance.