Renal Aldosterone Receptors: Studies with [3H]Aldosterone and the Anti-Mineralocorticoid [3H]Spirolactone (SC-26304)

In vivo, a spirolactone (SC-26304) inhibited the effects of aldosterone on urinary K⁺:Na⁺ ratios and the binding of [³H]aldosterone to renal cytoplasmic and nuclear receptors. Cytoplasmic binding of [³H]aldosterone and [³H]spirolactone (SC-26304) was similar in magnitude and involved the same set of sites. Under three sets of conditions-(i) in the intact rat, (ii) in kidney slices, and (iii) in reconstitution studies (mixing prelabeled cytoplasm with either purified renal nuclei or chromatin), [³H]spirolactone (SC-26304) did not yield specific nuclear complexes in contrast to the reproducible generation of these complexes with [³H]aldosterone. In glycerol density gradients, cytoplasmic [³H]aldosterone receptor complexes sedimented at 8.5 S and 4 S in low concentrations of salt and at 4.5 S in high concentrations of salt. Cytoplasmic [³H]spirolactone (SC-26304) receptor complexes sedimented at 3 S in low concentrations of salt and 4 S in high concentrations of salt. These results are discussed in terms of an allosteric model of the receptor system.