Binding of 3H-dexamethasone and 3H-corticosterone to rat liver cytosol during postnatal period.

The binding of 3H-dexamethasone (3H-Dx) and 3H-corticosterone (3H-B) to specific binding proteins of rat liver cytosol was compared during pre- and postnatal period. The binding of 3H-Dx was almost twice as high as that of 3H-B during the whole postnatal period. The Scatchard analysis showed a number of binding sites for 3H-Dx to be 4.44 X 10(-13) mol mg-1 (Kd 5.9 X 10(-9) mol 1(-1)) and for 3H-B to be 2.7 X 10(-13) mol mg-1 (Kd 1.6 X 10(-8) mol 1(-1)). A negative relationship between the binding of 3H-Dx to the rat liver cytosol receptors and the level of plasma corticosterone was found and it was concluded that thenumber of free receptors is, to the certain extent, dependent on thelevel of endogenous corticosteron. In spite of that, however, it seems that, in addition to corticosterone, the undetectability of receptors during a short period after birth may be due to some other factors.