Ontogenesis of glucocorticoid receptors in anterior pituitary gland: transient dissociation among cytroplasmic receptor density, nuclear uptake, and regulation of corticotropic activity.
The present investigation was undertaken to define the developmental pattern of glucocorticoid binding to the anterior pituitary gland and ascertain whether that binding correlated to modulation of corticotropin-releasing factor-induced release of ACTH. Scatchard analysis of data revealed the presence in cytosol (besides classical receptor sites interacting with both [3H]dexamethasone and [3H]corticosterone) of a transcortin-like component binding only the natural steroid. Whereas the number of sites of the former binder was not significantly altered during maturation and remained close to the adult value (276 +/- 12 fmol/mg protein), that of the latter declined dramatically after birth and rose again after postnatal day 10. The apparent Kd, however, remained unchanged. Transfer of te [3H]dexamethasone-receptor complex to nuclei of pituitary cells from neonates 2-6 days of age was found to be 20% that of adults despite the presence of comparable concentrations of receptor sites. Mixing experiments carried out with cytosol and nuclear fractions from different origins pointed to the cytoplasmic compartment as being implicated in this discrepancy. It was not until after postnatal day 10 that nuclear transfer reached mature levels. Although the extent of nuclear uptake and the magnitude of inhibition of ACTH secretion, as judged by means of a perifusion system, correlated well in hypophyses from 10- to 30-day-old neonates and adults, steroid binding and induction of biological response at earlier time points were less closely related. The results indicate the existence during development of a transient dissociation between cytosol and nuclear binding of corticosteroids by the anterior pituitary as well as between the latter process and blockade of ACTH release. These data are discussed in connection with the postnatal period nonresponse to stress. (Endocrinology 108: 591, 1981)