| Abstract: | Rat hypothalamic blocks incubated in vitro were used to study the characteristics of binding of 3H]dexamethasone and other steroids to cytosolic binding sites. Cytosols prepared following incubation of the tissue with 3H]dexamethasone for 2 h contained specifically bound steroid in amounts that depended upon the concentration of potassium (but not sodium) ions in the extracting buffer. There was an increase in bound 3H]dexamethasone extracted as the potassium ion concentration increased up to 0.1 M, but not beyond. Dexamethasone, when added to hypothalami in vitro caused a biphasic inhibition of bioactive corticotrophin-releasing factor (CRF) release, and the extent of the second phase of inhibition was dose-related. 11-Epicortisol, when added in a 100-fold molar excess over dexamethasone was able to prevent the second phase of inhibition caused by the latter steroid, as in the binding studies it was able to cause a 50% reduction in the binding of 3H]dexamethasone. In the functional studies it was shown that 11-epicortisol was able to "rescue" the tissue from dexamethasone-mediated delayed inhibition of CRF secretion if added to the blocks 30 min (but not later) after the agonistic steroid. |
