Interactions in vivo and in vitro of corticoids and progesterone with cell nuclei and soluble macromolecules from rat brain regions and pituitary.

Adrenalectomized-ovariectomized (ADX-OVX) rats were given tail vein infusions of [3H]corticosterone, dexamethasone, cortisol, deoxycorticosterone or progesterone in doses around 10 nmoles/kg body weight. After a 30-60 min uptake period, cell nuclei were isolated from 9 brain regions and pituitary. Patterns of cell nuclear retention of [3H]corticosterone and [3H]dexamethasone differed: the former steroid was highest in hippocampus and septum and low in pituitary; the latter steroid was highest in pituitary and more uniformly distributed in the brain. The other 3H steroids showed very little cell nuclear labeling in vivo. In contrast, in vitro cytosol binding in hippocampus for [3H]progesterone, cortisol, deoxycorticosterone, and dexamethasone was 40-60% of that observed for [3H]corticosterone. The specificity of cell nuclear binding in slices of hippocampus in vitro was similar to that observed for cytosol binding. Reasons for the selectivity of in vivo cell nuclear labeling remain to be discovered but the selectivity does not appear to be an intrinsic feature of the receptors themselves. The pattern of in vivo labeling by [3H]corticosterone and [3H]dexamethasone differs from the in vivo distribution of [3H]estradiol in ADX-OVX rats using the same dissection procedure and this demonstrates the regional differentiation within brain of steroid hormone uptake and 'receptor' processes.