The maximal glucocorticoid responsiveness and the adaptation degree are reduced in old rat liver as demonstrated by cortisol stimulation of RNA polymerases. Nevertheless the concentration of unoccupied 3H-dexamethasone binding sites in molybdate-stabilized cytosol of adrenalectomized old animals is significantly increased in comparison with young adult rats. The KD constants showed an increasing tendency, but not a significant one. In the molybdate-free cytosol the results are similar. First studies of the binding kinetics in the molybdate-free system showed a sigmoidal saturation curve in the cytosol of young adult rats, but usual hyperbolic saturation kinetics in the cytosol of old animals. The Hill coefficient was 1.0 ± 0.1 for old and 1.9 ± 0.3 for young animals. The binding of activated 3H-dexamethasone receptor complexes to liver nuclei showed no significant age-dependent differences in binding kinetics, acceptor site concentration or affinity. Attention must be paid to altered glucocorticoid receptor binding in the cytosol and in nuclei as a potential cause of changes in hormone-induced gene expression at the pretranscriptional level.

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