title: Corticosteroid receptors in liver cytosol of the clawed toad, Xenopus laevis: daily and seasonal variations.
abstract: In postmetamorphic Xenopus laevis liver cytosol the glucocorticoid binding capacity R0 and the dissociation constant Kd were determined. The receptor assay included an incubation period of 24 hr at 0-4 degrees with sodium molybdate to stabilize the receptor. Dexamethasone, triamcinolone acetonide, and corticosterone as tritiated ligands were compared regarding the R0 (67.6, 57.2, and 30.7 fmol/mg protein), the Kd (3.54, 0.56, and 9.03 nM), and the rate of dissociation in young specimens of X. laevis. In adult toads the [3H]dexamethasone receptor binding capacity was threefold higher in females than in males (153.86 +/- 12.19, 54.29 +/- 4.5 fmol/mg protein)--with about the same Kd (3.97 +/- 0.57, 4.08 +/- 0.28 nM). Young toads were kept under an artificial light regime (light from 600 to 1800 hr) and dexamethasone binding was measured every 3 hr. Unlike Kd, R0 showed a significant diurnal variation with maximal values at 600 and 1800 hr, which occurred about 9 hr after a maximal level of corticosterone in serum was reached (900, 2100). Seasonal variations of the [3H]dexamethasone and [3H]corticosterone binding capacity were different in both sexes of adult X. laevis. Maximal values in males were found in June/July and October/November. In females, the R0 was increased in the second half of the year with the maximum in August (275.5 +/- 45.02 fmol/mg protein). No correlation between R0 and the concentrations of corticosterone or aldosterone existed.
authors.affiliation: Department of Zoology, University Karlsruhe, Federal Republic of Germany.
authors.forename: C B
authors.initials: CB
authors.lastname: Lange
authors.forename: W
authors.initials: W
authors.lastname: Hanke
mesh_terms: D000450:Aldosterone / Q000097:blood; D000818:Animals; D002940:Circadian Rhythm; D003345:Corticosterone / Q000097:blood; D003600:Cytosol / Q000032:analysis; D005260:Female; D008099:Liver / Q000032:analysis*; D008297:Male; D010507:Periodicity; D011965:Receptors, Glucocorticoid / Q000032:analysis*; D011987:Receptors, Steroid; D012621:Seasons; D014982:Xenopus laevis / Q000378:metabolism*
chemical_list: D011965:Receptors, Glucocorticoid; D011987:Receptors, Steroid; C024357:corticosterone receptor; C028697:dexamethasone receptor; C039250:triamcinolone acetonide receptor; D000450:Aldosterone; D003345:Corticosterone