Mineralocorticosteroid receptors in the foetal compartment

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Mineralocorticosteroid receptors have been found in the foetal kidney of the guinea pig (at 25–40 days of gestation) in experiments carried out both in vivo and in vitro. More than 50% of the total d-aldosterone receptors were found in the nucleus. 20% of the total nuclear radio-activity was extracted by the 0.1 M Tris-HCl solution and 50% by the 1 M NaCl -0.01 M Tris solution, suggesting that at this period of the foetal evolution the aldosterone receptors are localized principally in the chromatin fraction. The formation of these [ 3H]-aldosteronc-macro-molecule complexes is very rapid, maximum values being found at 4 min of incubation at 37°C. The nuclear receptors, but not those of the cytosol fraction, are temperature-dependent, d-Aldosterone and deoxycorticosterone compete with the [ 3H]-aldosterone complex. On the other hand, d-aldosterone has no effect on the [ 3H]-aldosterone-macromolecule complex if reincubation is carried out with the nuclear extracts (at 4°C) after extraction. Also, the 0.1 M Tris and 0.01 M Tris-1 M NaCl nuclear extracts do not form [ 3H]-aldosterone complexes after incubation (separately or combined) at 4°C or 37°C, suggesting that the configuration necessary for the formation of the [ 3H]-aldosterone complexes is altered by the extraction procedure. Incubation of the purified nucleus produces more [ 3H]-aldosterone-macromolecule complexes (per mg of protein) than incubation with the total cell or with the crude nuclear fraction. These data suggest that unbound aldosterone can cross the nuclear membrane and form the aldosterone complexes without the participation of a cytosol intermediate.