Further studies on the cytoplasmic 3H-dexamethasone receptor in the liver from adult and fetal rats.

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Abstract
The binding characteristics of cytoplasmic receptor to DEX [dexamethasone] in livers of adult and fetal rats were further examined to lend insight into the mechanism of age-related changes in responsiveness to glucocorticoids. Cytoplasmic DEX-receptor complexes in both adult and fetal livers were mainly precipitated with 35% saturation of (NH4)2SO4 and eluted immediately after a void volume from a Sephadex G-100 column. When the 35% (NH4)SO4 fraction was applied to DEAE chromatography, 2 peaks of the radioactivity bound to protein, eluted with 50 mM and 100 mM KCl, were observed in the adult liver. Only 1 peak which was eluted with 50 mM KCl was noticed in the fetal liver. Stability of the DEX-receptor complex during incubation at 0 or 23.degree. C was not significantly different in these 2 tissues. At least 2 DEX-binding components which exhibited RBPB [RF using electrophoretic marker bromophenol blue] 0.28 and RBPB 0.43 in polyacrylamide gel electrophoresis were demonstrated in the cytoplasm from the adult liver, while 1 clear peak with RBPB 0.25 was observed in the fetal liver. The binding in the adult cytosol to DEX was efficiently inhibited by addition of corticosterone and cortisol and the similar inhibition by these 2 steroids was observed in the latter tissue, deoxycorticosterone and progesterone also competed with DEX binding moderately. Two forms of DEX-receptor complex 1 binds only to nuclei and the other binds to DNA and nuclei were observed in the fetal liver cytosol as well as in the adult. The binding capacity of these 2 forms of receptor was almost comparable in cytosols of 2 tissues examined. The nuclear binding of 3H-DEX in the isolated liver cells was also different in fetal and adult animals.