Physicochemical characterization of hepatic glucocorticoid receptors from pre- and post-weaned mice.

The physicochemical parameters viz., molecular weight, stokes radius and ionic state of hepatic glucocorticoid receptors from pre-(10-day) and post-(60-day) weaned mice were studied. Gel permeation studies of the crude receptors showed a molecular mass of approximately 290 kDa for the unactivated receptors from both the age groups while the thermally activated receptors showed a molecular mass of approximately 90 kDa. The stokes radii were approximately 5.8 and 3.6 for the unactivated and activated receptors, respectively from both the age groups studied. Elution of the bound glucocorticoid receptors from anion-exchanger did not reveal any charge difference in the two age groups; the unactivated receptors eluted at approximately 250 mM KCl whereas the activated receptors eluted at approximately 100 mM KCl. Salt extraction of thermally activated nuclear bound receptors and immunological studies on the unactivated receptors revealed no age-related variation in the two groups of mice. Our findings confirm that the physicochemical properties of hepatic glucocorticoid receptors remain unchanged at these developmental stages of mice.

Postnatal changes in kidney glucocorticoid receptor of mice.

The specific binding of [3H]dexamethasone to its receptor and the activation of the hormone-receptor complexes from the kidney of mice at various postnatal ages were investigated. The results indicated that the level (fmol/mg protein) of glucocorticoid receptors remained unaltered at 10-, 15- and 30-day, increased significantly at 45-day and thereafter declined to its earlier level in 60-day old mice. Scatchard analysis of binding data confirmed the increased level of receptors at 45-day compared to day 15, without any change in the hormone affinity to its receptor at these two ages. The extent of temperature- and salt-dependent activation of the receptor showed no marked differences in 10- and 60-day old mice, as determined by DNA-cellulose binding assays. However, the nuclear binding of temperature- and salt-activated glucocorticoid-receptor complexes was significantly higher in 10-day old mice. Cross-mixing experiments showed nuclear specificity in higher binding of thermally activated receptor at day 10 of postnatal age. Molybdate, tungstate and N-ethylmaleimide inhibited the temperature- and salt-dependent activation of glucocorticoid-receptor complexes similarly at both the ages studied. DNase I extraction of bound hormone-receptor complexes from nuclei showed higher extractability at day 10 (63%) compared to day 60 (43%). These findings indicated changes in glucocorticoid receptor concentration together with chromatin organization that might play an important role in glucocorticoid-mediated responses during postnatal development of mice.