title: Relative binding affinity of steroids for the corticosterone receptor system in rat hippocampus.
abstract: In cytosol of the hippocampus corticosterone displays highest affinity for the sites that remain available for binding in the presence of excess RU 26988, which is shown to be a "pure" glucocorticoid. A rather high affinity (greater than or equal to 25%) was found for 11 beta-hydroxyprogesterone, 21-hydroxyprogesterone, 5 alpha-corticosterone, 19-nor-deoxycorticosterone, 11-deoxycorticosterone and cortisol. A moderate affinity (greater than 5% and less than 25%) was displayed by about 14 steroids among which progesterone, aldosterone, 9 alpha-fluorocortisol and dexamethasone. Corticosterone also shows highest affinity to plasma transcortin and thymus cytosol in the presence of RU 26988. However, the rank-order in affinity by the competing steroids was distinctly different from that observed in the hippocampus; cf. aldosterone and dexamethasone displaced [3H]corticosterone from sites unoccupied by RU 26988 in the hippocampus but not from transcortin or sites in thymus cytosol. In thymus cytosol some potent glucocorticoids have higher affinity for the [3H]dexamethasone labeled sites than dexamethasone. The binding of [3H]dexamethasone in thymus cytosol is completely abolished in the presence of a 100-fold excess of RU 26988. We conclude that our data support the evidence for RU 26988 as a selective ligand for glucocorticoid receptors. RU 26988 leaves binding sites available with highest affinity for corticosterone in hippocampus cytosol that are distinct from transcortin-like sites as found in thymus cytosol or from plasma transcortin.
mesh_terms: D000732:Androstanols / Q000378:metabolism; D000818:Animals; D001667:Binding, Competitive; D003345:Corticosterone / Q000378:metabolism*; D003907:Dexamethasone / Q000378:metabolism; D006624:Hippocampus / Q000378:metabolism*; D008024:Ligands; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D011965:Receptors, Glucocorticoid / Q000378:metabolism*; D011987:Receptors, Steroid / Q000378:metabolism*; D013950:Thymus Gland / Q000378:metabolism
chemical_list: D000732:Androstanols; D008024:Ligands; D011965:Receptors, Glucocorticoid; D011987:Receptors, Steroid; C024357:corticosterone receptor; C038341:RU 26988; D003907:Dexamethasone; D003345:Corticosterone