Absence of hydrocortisone from cytoplasmic hormone-protein complexes formed in vivo after administration of biologically active doses of [3H]hydrocortisone

Localization of the glucocorticoid receptor in rat liver cells: evidence for plasma membrane bound receptor

1. The cytoplasmic glucocorticoid receptor of rat liver cells is in part recovered in the plasma membrane fraction. 2. After in vivo administration of [3H]dexamethasone, 0.35% of the radioactivity recovered is bound on plasma membranes. 3. Dexamethasone also binds in vitro specifically to plasma membranes. Expressed as fmol/mg protein, binding of dexamethasone to plasma membranes is comparable to binding to the soluble cytoplasmic fraction (cytosol). 4. Using polyclonal antibody to the glucocorticoid receptor and the indirect immunofluorescence technic, an intense decoration of the plasma membranes is observed, denoting a high concentration of glucocorticoid receptor on plasma membranes. 5. The localization of the receptor on plasma membranes could be of potential importance for its interaction with agents (mitogens, growth factors) initially acting on the cell membrane, regulating subsequent cell proliferation and growth at the level of the cell nucleus.

Glucocorticoids and the isolated rat hepatocyte

Following incubation at 37 degrees C with tritiated glucocorticoids isolated hepatocytes prepared from non-adrenalectomized rats show rapid uptake of label. Uptake is non-saturable, and non-linear over the first 60 sec of exposure to steroids. HPLC separation of aqueous extracts of cells and incubation medium shows that polar metabolites of the natural steroid, corticosterone, appear within 10 sec, whereas the synthetic glucocorticoid, dexamethasone, is not altered. Our results suggest that diffusion is the most important process by which glucocorticoids enter liver cells, and that the predominant fate of corticosterone is rapid metabolism.

High plasma steroid levels in the squirrel monkey: deficient receptors or metabolism?

Many New World primates such as the squirrel monkey have extraordinarily high plasma steroid hormone levels as compared to humans and Old World primates. To clarify the mechanism(s) underlying this apparent steroid resistance, glucocorticoid and androgen binding to putative receptors in genital skin fibroblasts from several species was investigated. Differences in either affinity and/or number of binding sites were found but these were small compared to the very large differences in total or free plasma steroid concentrations between Old and New World primate species. In contrast, when the ability of fibroblasts to metabolize testosterone was compared, squirrel monkey cells were devoid of 5 alpha-reductase activity which was readily demonstrated in human cells. Together with other data indicating that squirrel monkeys excrete little if any 5 alpha- or 5 beta-reduced urinary steroid metabolites, these results suggest that inefficient metabolism rather than receptor binding abnormalities may account for the elevated plasma hormone levels in the squirrel monkey.

Immunochemical studies on biosynthesis of rat plasma angiotensinogen and its regulation by cortisol

Glucocorticosteroid hormones increase the level of rat plasma angiotensinogen by increasing its rate of synthesis. Two forms of plasma angiotensinogen have been purified differing with respect to molecular weight and affinity to concanavalin A. Immunochemical studies using antibodies raised against the separated forms of angiotensinogen revealed cross-reactivity with both antigens. Both antibodies were able to quantitatively precipitate the angiotensinogen activity present in rat serum samples. Cortisol increased the total amount of plasma renin substrate without changing the relative amounts of both angiotensinogen forms. mRNA coding for plasma angiotensinogen was determined by in vitro translation of poly(A)-containing RNA and immunochemical analysis of translation products. Angiotensinogen mRNA could be detected in total poly(A)-containing RNA isolated from rat liver, but not in mRNA isolated from brain, although angiotensinogen has been reported to be present in the latter organ. The level of hepatic mRNA coding for plasma angiotensinogen was high in rats treated with cortisol, but not detectable in animals depleted from endogenous glucocorticosteroids by bilateral adrenalectomy.

No correlation between binding of glucocorticosteroids to specific cytoplasmic proteins in vivo and enzyme induction in the rat liver

Time- and dose-dependence of the formation of the different cytoplasmic hormone-protein complexes were studied in the rat liver after administration in vivo of [3H]cortisol or [3H]dexamethasone and compared with the stimulation of RNA polymerase B and induction of tyrosine aminotransferase and tryptophan oxygenase. No correlation could be found between formation in vivo of any of the five cytoplasmic hormone-protein complexes found and stimulation of RNA polymerase B activity or enzyme induction. After administration of [3H]cortisol, different metabolites of cortisol could be demonstrated in the isolated hormone-protein complexes. No time- or dose-dependence of the metabolite patterns could be observed after application of hormone doses that were in the range of the biologically active doses. After administration of [3H]dexamethasone, the same hormone-protein complexes were observed, which contained, however, the injected steroid instead of metabolites. These results seem to indicate that the cytoplasmic binding components present in the rat liver are enzymes involved in the metabolism of the glucocorticosteroids and that dexamethasone binds to these enzymes as a substrate analogue.

Influence of the adrenal gland on uptake, retention, metabolism and binding to cytoplasmic proteins of [3H] cortisol by the rat liver

The effects of adrenalectomy on uptake, retention, metabolism and in vivo binding to cytoplasmic proteins of [3H]cortisol in the rat liver were studied. The same amount of radioactivity was accumulated in the different subcellular fractions of liver of adrenalectomized and normal male rats 30 min after intraperitoneal injection of a biologically active dose of [3H]-cortisol. However, the accumulated radioactivity, with exception of microsomes, was lost more rapidly from all subcellular fractions of normal than of adrenalectomized animals. The pattern of non-conjugated metabolites present in the cytosol also showed differences between adrenalectomized and normal rats. Analysis of the hormone-protein complexes formed in vivo after application of a biologically active dose of [3H]cortisol, revealed that the amount of hormone-protein complexes was lower in cytosol of adrenalectomized animals than in normal rats. Analysis of the individual hormone-protein complexes formed in vivo revealed that DE-1b, DE-2 and DE-3 were less prominent in adrenalectomized than in normal rats, whereas the level of DE-1 was found to be essentially independent from the adrenal state.