Further chemical differentiation of type I and type II adrenocorticosteroid receptors in mouse brain cytosol: evidence for a new class of glucocorticoid receptors

Characterization of mineralocorticoid and glucocorticoid receptors in primate brain

Characteristics of neural corticosteroid receptors were studied in 51 adrenally-intact macaque monkeys using a modification of a corticosteroid receptor assay developed in this laboratory for rodent studies. Using cortisol as a ligand, two receptor subtypes could be distinguished and with similar Kd's to those observed in rodents, as measured with corticosterone. The time course showed maximum binding for mineralocorticoid receptors at 24 h and for glucocorticoid at 4 h. There were regional differences in the number of available binding sites for each receptor type, as well as an inverse correlation between the concentration of cortisol in the blood at the time of death and the number of available binding sites. In general this paper emphasizes the similarities between such receptors in primate and those in other species, similarities that could be detected despite the technical constraints of studying tissue taken from non-adrenalectomized animals.

H-2 gene complex and corticosteroid responsiveness: evidence that the corticosteroid hormone signal transduction pathway in the adult mouse lung is not associated with haplotype-specific responses to corticosteroids

Differential responsiveness to corticosteroids (CORT) has been shown to be related to HLA haplotype. A strong association between the mouse homolog to the human HLA complex, the H-2 complex, and intrauterine responses to CORT have also been demonstrated; haplotype differences alter CORT-induced susceptibility to cleft palate and temporal differences in lung maturation. Since variation in the glucocorticoid receptor (GR) is associated with tissue specific responses to CORT, we hypothesize that haplotype-specific CORT responsiveness may be regulated by H-2 associated modification of GR expression and/or function. Given that H-2 congenic mice are genetically identical except at the H-2 complex on mouse chromosome 17 and the GR structural gene is encoded on chromosome 18, the GR gene is identical in these mice. However, any step in the GR signal transduction pathway may be regulated by gene(s) at or near the H-2 complex and result in haplotype-specific differences in CORT responsiveness. We have investigated differences in qualitative and quantitative characteristics of the adult B10 (H-2b) and B10.A (H-2a) pulmonary GR by Scatchard analysis, immunochemical and biochemical assays. No differences in the GR binding parameters (BMAX and Kd), receptor form and level, or ligand-GR complex binding to glucocorticoid response element (GR-GRE) were detected, leading us to conclude that H-2 associated factors do not regulate the relative intrauterine responses to CORT by modulating the adult GR.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased type II glucocorticoid-receptor numbers and glucocorticoid-sensitive enzyme activities in the brain of the obese Zucker rat

The possibility that the glucocorticoid-dependence of obesity of the obese fa/fa rat reflects on overactivity of glucocorticoids on the brain has been investigated by studies of enzyme activities and glucocorticoid type II (GR) receptors. The activity of 2 glucocorticoid-sensitive enzymes, glycerol-3-phosphate dehydrogenase and glutamine synthetase, were increased in the hippocampus of obese rats. In contrast malate dehydrogenase and pyruvate kinase, glucocorticoid-insensitive enzymes, were normal. Adrenalectomy of obese rats reduced glycerol-3-phosphate dehydrogenase activity to the level of lean rats. Scatchard analysis of [3H]corticosterone binding showed that the number of type II (GR) receptors was increased in the hypothalamus and hippocampus of obese rats but the affinity of these receptors was reduced. The evidence supports the hypothesis of excessive central glucocorticoid activity in the obese rat.

Glucocorticoid receptors and enzyme induction in the spinal cord of rats: effects of acute transection

The spinal cord is a glucocorticoid-responsive tissue, as demonstrated by hormonal effects on enzyme induction and by the presence of type II and type I glucocorticoid receptors in cytoplasmic extracts of this CNS region. Using microdissection techniques, we have found in the present investigation that glucocorticoid type II receptors are the most abundant class detected in gray (ventral and dorsal horns) and white (lateral funiculus) matter and that the distribution of type II sites among these regions was quantitatively similar. Type I sites were also quantified, with a slight prevalence in gray matter as opposed to white matter. Furthermore, stimulation of an inducible enzyme, ornithine decarboxylase (ODC), was found in ventral horn and lateral funiculus but not in dorsal horn after administration of dexamethasone (DEX), a type II receptor ligand. We also found that surgical transection of the spinal cord, while markedly increasing ODC activity per se, did not prevent the stimulatory effect of DEX administration on ODC activity measured in the lumbar enlargement of the spinal cord located below the surgical lesion. Taken together, the results suggest a direct effect of glucocorticoids on ODC activity in the spinal cord of rats, probably mediated by glucocorticoid receptors (type II) found in target cells of the ventral horn and lateral funiculus. The results also indicate that glucocorticoid receptors of the dorsal horn were not involved in ODC induction, and a function for these receptors awaits the results of further experimentation.

Presence of type I and type II/IB receptors for adrenocorticosteroid hormones in the inner ear

Aldosterone-Type I and dexamethasone-Type II/IB receptor complexes were identified in cytosol prepared from both cochlear and vestibular tissue samples. The specific binding capacity of Type I receptors in the cochlear tissues was approximately equal to that in the vestibular tissues. Likewise, the binding capacity of Type II/IB receptors in the cochlea was approximately equal to that in the vestibular endorgans. Based on the total specific binding measured with dexamethasone, the Type II/IB receptors appeared to outnumber the Type I receptors in cochlear and vestibular tissues by a factor of approximately 2.6; however, when adjustments were made for the probable cross-binding of dexamethasone to Type I receptors, these ratios were decreased to approximately 1.6. The existence of protein receptors for adrenocorticosteroid hormones demonstrated in the present study clearly suggests a mechanism whereby such hormones may directly regulate fluid and ionic gradients in the inner ear.

Induction of ketone body enzymes in glial cells

Ketone bodies serve a dual function in developing brain. They are important sources of energy for metabolism and serve as precursors for lipid synthesis. Astrocytes have two to three times higher activity than oligodendroglia for one of the enzymes involved in ketone body metabolism, 3-ketoacid-CoA transferase. Both glial cell types have similar levels of activity for beta-hydroxybutyrate dehydrogenase. Glucocorticoids and dibutytyl cAMP produce a significant stimulation of activity of both enzymes in astrocytes and oligodendroglia. However, the most striking induction in activity of the two enzymes is in the presence of hydrocortisone and sodium butyrate. There is a three- to eightfold stimulation with these effectors in both astrocytes and oligodendroglia. Thus, in brain the expression of ketone body enzyme activities is finely regulated by hormones and by agents that increase cAMP levels.

Treatment of mouse brain cytosol with dextran-coated charcoal and high salt does not reveal a new glucocorticoid binder

Incubation of steroid-free whole mouse brain cytosol from adrenalectomized-ovariectomized mice with saturating concentrations of tritiated dexamethasone was found to label all Type I as well as all Type II adrenocorticosteroid receptors. The quantitative and brain regional distribution of residual dexamethasone binding in cytosols pre-treated with dextran-coated charcoal (DCC) and 300 mM KCl was indistinguishable from that for tritiated aldosterone-Type I receptor complexes under the same conditions. We therefore conclude that the dexamethasone binding sites remaining after DCC and KCl treatment of steroid-free brain cytosol are due to the presence of Type I receptors. The differential sensitivity of Type I and Type II receptors to the DCC/KCl treatment paradigm may be useful in the purification of Type I receptors.

Adrenocorticoid action in the spinal cord: some unique molecular properties of glucocorticoid receptors

1. Glucocorticoid hormones affect several functions of the spinal cord, such as synaptic transmission, biogenic amine content, lipid metabolism, and the activity of some enzymes (ornithine decarboxylase, glycerolphosphate dehydrogenase), indicating that this tissue is a target of adrenal hormones. 2. Corticosterone, the main glucocorticoid of the rat, is detected at all regional levels of the spinal cord, and cold stress increases this steroid, predominantly in the cervical regions. 3. Intracellular glucocorticoid receptors have been found in the spinal cord, with higher concentrations in the cervical and lumbar enlargements. Prima facie, these receptors presented biochemical, stereospecifical, and physicochemical properties similar to those of receptors found in other regions of the nervous system. The prevalent form in the spinal cord is the type II receptor, although type I is also present in small amounts. 4. The type II glucocorticoid receptor of the spinal cord shows an affinity lower (Kd 3.5 nM) than that of the hippocampal type II site (Kd 0.7 nM) when incubated with [3H]dexamethasone. This condition may impair the nuclear translocation of the spinal cord receptor. 5. Another peculiar property of spinal cord type II site is a greater affinity for DNA-cellulose binding than the hippocampal receptor during heat-induced transformation. Also, the spinal cord receptor shows resistance to the action of RNAse A, an enzyme which increases DNA-cellulose binding of the hippocampal receptor, indicating that both receptors may be structurally different. 6. Therefore, it is possible that a different subclass of type II, or "classical glucocorticoid receptor," is present in the spinal cord. This possibility makes the cord a useful system for studying diversity of glucocorticoid receptors of the nervous system, especially the relationship between receptor structure and function.

Differential up- and down-regulation of type I and type II receptors for adrenocorticosteroid hormones in mouse brain

Adult female mice were adrenalectomized and ovariectomized and the concentration of Type I and Type II receptors in whole brain, kidney, and liver cytosol determined at various time thereafter by incubation with [3H]aldosterone (+ RU 26988 to prevent binding to Type II receptors) or [3H]dexamethasone, respectively. Type I receptor binding in brain was found to undergo a dramatic biphasic up-regulation, with levels six times that of intact levels by 24 h post-surgery and a doubling again by 4-8 days post-surgery. By 16 days, however, Type I specific binding had returned to intact levels. Similar, but less dramatic fluctuations were seen in kidney and liver, whereas much smaller fluctuations were seen for Type II receptors in all three tissues. In a follow-up study with Scatchard analyses we observed a similar transient up- and down-regulation in maximal binding for Type I, and to a lesser extent Type II receptors in all three tissues. As expected, the apparent binding affinity for both receptors increased after surgical removal of competing endogenous steroids. Radioimmunoassays revealed that plasma concentrations of corticosterone were reduced to near undetectable levels by 24 h post-surgery. A direct comparison of male and female mice revealed no sex-related differences in Type I receptor binding capacity fluctuations in brain cytosol after adrenalectomy-gonadectomy. Lastly, treatment with exogenous aldosterone or corticosterone was found to prevent adrenalectomy-gonadectomy-induced up-regulation of Type I and, to a lesser extent, Type II receptors in brain. Somewhat surprisingly, the potency of these two adrenocorticosteroids appeared to be very similar for both receptor types.

Corticosterone's dual metabolic actions

Corticosterone possesses two distinctly opposite metabolic actions. The actions are strictly dose-dependent and are linked to type I and type II corticosteroid receptor binding. These conclusions are drawn from continuous infusion studies where corticosterone yields a bitonic dose-response curve for body weight gain and feeding efficiency. Anabolic at low serum levels, corticosterone concentrations above 2 micrograms/dl bring about an opponent catabolic process that intensifies and eventually masks the anabolic action. Relatively pure type I (aldosterone) and type II (RU28362 and dexamethasone) corticosterone receptor agonists produce opposite monotonic functions that respectively mimic the ascending and descending arms of the corticosterone dose-response curve. Stimulation of either receptor increases the proportion of carcass fat to lean body mass by either increasing carcass lipids (type I) or by reducing protein (type II).