Efficacy of five methods for the bound-free separation of gluco- and mineralocorticoids from type I, II and III receptors found in hepes- and tris-buffered mouse brain cytosol

Chronic intermittent stress does not differentially alter brain corticosteroid receptor densities in rats prenatally exposed to ethanol

Prenatal ethanol exposure produces hypothalamic-pituitary-adrenal (HPA) hyperresponsiveness to stressors. The present study tested the hypothesis that decreased corticosteroid receptor densities at HPA feedback sites may play a role in deficient feedback inhibition and the resultant HPA hyperresponsiveness that is observed following prenatal ethanol exposure. Brains of adult Sprague-Dawley rats from prenatal ethanol (E), pair-fed (PF) and ad libitum-fed control (C) treatment groups were examined for both mineralocorticoid receptor (MR; Type I) and glucocorticoid receptor (GR; Type II) densities using a cytosolic binding assay. Experiment 1 compared the effects of chronic intermittent stress (Stress Regimen I) and corticosterone (CORT) pellet implants on hippocampal corticosteroid receptor densities in control rats. Experiment 2 determined whether exposure to Stress Regimen I would differentially downregulate and whether adrenalectomy (ADX) would differentially upregulate hippocampal corticosteroid receptors in E compared with PF and C animals. Experiment 3 examined the effects of a modified chronic intermittent stress regimen (Stress Regimen II) on corticosteroid receptor densities at several HPA feedback sites (hippocampus, prefrontal cortex, hypothalamus, and anterior pituitary) in E compared with PF and C animals. CORT pellet implants significantly downregulated hippocampal GR and MR densities in control males and females. Exposure to Stress Regimen I produced downregulation of hippocampal GRs and MRs in males comparable with that produced with CORT pellet implants, and significant downregulation of hippocampal GRs in females across all prenatal treatment groups. This stress regimen also elevated basal plasma CORT levels without concurrent changes in plasma CBG levels, and increased relative adrenal weights in both males and females. In addition, upregulation of hippocampal GRs occurred at 7 days compared with 24 h following ADX in females that had previously been exposed to this stress regimen. Following exposure to Stress Regimen II, both the downregulation of hippocampal corticosteroid receptors and the increase in basal CORT levels in males and females appear to have been abolished by the changes in housing condition during the period of chronic stress. Importantly, prenatal ethanol exposure did not differentially alter GR or MR densities at any feedback site under non-stressed conditions. Exposure to Stress Regimen II, revealed subtle effects of prenatal treatments on hippocampal GRs however it is unlikely that these changes in corticosteroid receptor densities mediated the feedback inhibition deficits observed in E animals. Together, these data demonstrate that: (1) a relatively mild intermittent stress regimen can increase basal CORT levels and downregulate hippocampal corticosteroid receptor densities (2) a seemingly small change in housing conditions during stress appears to eliminate both receptor downregulation and increase in basal CORT levels and (3) decreased corticosteroid receptor densities at HPA feedback sites in the brain do not appear to underlie the HPA hyperresponsiveness observed in E animals.

Differential effects of pregnancy on mineralocorticoid and glucocorticoid receptor availability and immunoreactivity in cortisol feedback sites

The suppression of plasma adrenocorticotropic hormone by very low levels of cortisol is reduced in pregnant adrenalectomized ewes, suggesting that pregnancy reduces the efficacy of the high-affinity corticosteroid receptor. This study was designed to determine the effects of pregnancy on the availability, immunoreactivity, and affinity of both corticosteroid receptors: the high-affinity mineralocorticoid receptor (MR) and the lower-affinity glucocorticoid receptor (GR). Availability was measured in the hypothalamus, pituitary, hippocampus and kidney using a saturation point radioligand binding assay. GR availability was significantly decreased in hippocampal cytosols obtained from pregnant ewes, but did not significantly change in other tissues. This finding is consistent with increased GR activation due to elevated circulating concentrations of cortisol. MR availability significantly increased from undetectable levels in hippocampal cytosols obtained from nonpregnant ewes to 2.8 +/- 1.6 fmol/mg protein in pregnant ewes, suggesting a reduced MR activation in the hippocampus during pregnancy. MR availability tended to be greater in other tissues during pregnancy, but these differences were not significant. The amount of immunoreactive MR (iMR) and GR (iGR) protein was estimated by quantifying Western blots. iGR significantly increased in the pituitary, but did not significantly change in other tissues. In contrast, iMR was significantly increased during pregnancy in all tissues assayed, suggesting that an increased cytosolic MR protein amount contributes to the observed increase in MR availability. Since studies suggest that progesterone is a potent anticorticosteroid, we tested for evidence of endogenous inhibition of binding to MR and/or GR during pregnancy by determining MR and GR affinity in pituitary cytosols obtained from nonpregnant and pregnant ewes. Although there was a tendency towards a decreased affinity of the MR in pregnant ewes, there was no significant change in the K(D) of the pituitary MR or GR during pregnancy. We hypothesize that an alteration in activation and/or autoregulation of the MR during pregnancy, particularly in the hippocampus, may contribute to the observed changes in receptor availability and immunoreactivity and increase basal plasma cortisol levels during pregnancy.

Early handling can attenuate adverse effects of fetal ethanol exposure

The effects of early handling on physiological and hormonal responses of rats exposed to ethanol prenatally were studied. Male and female Sprague-Dawley rats from prenatal ethanol (E), pair-fed (PF), and ad lib-fed control (C) prenatal treatment groups were either handled (H) or nonhandled (NH) during the preweaning period and tested in adulthood. Early handling eliminated the deficit in preweaning weight gain observed in E compared to PF and C offspring. In adulthood, early handling eliminated the increased hypothermia observed in E and PF compared to C males following an ethanol challenge (2.0 g/kg, IP). In addition, H males displayed marginally less hypothermia overall than NH males. In contrast, handling accelerated the return to preinjection temperature in PF and C females but had no effect on E females. There were no significant differences among E, PF, and C rats in corticosterone (CORT) responses to ethanol challenge (1.5 g/kg, IP), but both males (marginally) and females in the H condition displayed higher CORT levels overall than NH rats. Early handling also eliminated the increased peak CORT response to restraint stress in E compared to C females, but did not affect the more prolonged elevation of CORT in E compared to PF and C females. There were no differences among E, PF, and C females in hippocampal type I and type II glucocorticoid receptor density or affinity. However, binding affinity of type II receptors was slightly but significantly increased in H compared to NH females. Together, these data indicate that early handling may modulate or attenuate some, but not all, of the adverse effects of fetal ethanol exposure on offspring growth and physiological responsiveness.

Stress response, adrenal steroid receptor levels and corticosteroid-binding globulin levels--a comparison between Sprague-Dawley, Fischer 344 and Lewis rats

Histocompatible Fischer 344 (F344) and Lewis (LEW) rats provide a comparative model for investigating the interactions between the nervous, endocrine and immune systems. The outbred Sprague-Dawley (SD) is the maternal strain for the inbred F344 and LEW strains. In this study we report large differences in the diurnal and stress corticosterone (CORT) profiles of these three genetically related strains: (1) F344 rats had significantly higher diurnal and stress CORT levels than SD and LEW rats; (2) in the morning, stress CORT levels of SD and F344 rats returned towards basal 1 h after cessation of the stressor, whereas stress CORT levels of LEW rats had not returned to basal by this time; and (3) in the evening, SD and F344 rats showed the expected evening rise in basal CORT levels, whereas LEW rats failed to show this rise. In light of the large differences in CORT levels, we expected to observe strain differences in absolute levels of Type I (mineralocorticoid) and Type II (glucocorticoid) adrenal steroid receptors in neural as well as immune tissue. However, we found no significant strain differences in levels of Type I receptors in the hippocampus, hypothalamus, pituitary, thymus, spleen and peripheral blood mononuclear cells. Similarly, we saw no significant strain differences in levels of Type II receptors in most of the tissues surveyed, with the notable exception that LEW rats showed higher Type II binding in the thymus, and SD rats showed small, but significantly higher Type II binding in the hippocampus. We also studied strain differences in levels of corticosteroid-binding globulin (CBG). F344 rats expressed significantly higher CBG levels than SD and LEW rats, in plasma, spleen and thymus. Future studies will investigate whether the substantial differences between strains in levels of CORT and CBG, in the context of few strain differences in post-adrenalectomy adrenal steroid receptor levels in neural and immune tissue, translate into differences in receptor occupancy/activation under resting conditions, or following stress.

Effects of prenatal ethanol exposure on glucocorticoid receptors in rat hippocampus

Animals exposed to ethanol in utero are typically hyperresponsive to stressors in adulthood as indicated by increased adrenocortical activation and/or deficits in response inhibition or recovery following stress. In the present study we reasoned that a deficit in feedback control of pituitary-adrenal activity might underlie this hyperresponsiveness in fetal ethanol-exposed (FEE) animals. Further, we hypothesized that a long-term decrease in hippocampal glucocorticoid receptor concentration, induced by prenatal ethanol exposure, might mediate such a deficit in pituitary-adrenal feedback regulation. Male and female Sprague-Dawley rats from prenatal ethanol (E), pair-fed (PF), and control (C) treatment groups were tested in adulthood for determination of cytosolic hippocampal glucocorticoid receptor binding. No significant differences in specific binding (Bmax) or binding affinity (Kd) of either type I or type II glucocorticoid receptors were found among animals from E, PF, and C conditions. There were, however, significant sex differences in receptor concentration and binding affinity; females showed significantly greater maximal binding and significantly lower binding affinity than males. These data do not support the hypothesis that prenatal ethanol exposure induces a long-term decrease in hippocampal glucocorticoid receptors in animals tested under basal nonstressed conditions. However, these data do not preclude the possibility that receptor binding capacity may be differentially affected in E, PF, and C animals during stress.

Ontogeny of dexamethasone binding and sodium potassium ATPase activity in experimental murine polycystic kidney disease

The induction of polycystic kidney disease (PKD) by glucocorticoids in newborn mice behaves as a "threshold" trait, with prevalence of PKD varying in different inbred strains after exposure to an inducing steroid. C3H mice (low threshold for PKD) demonstrated greater specific dexamethasone binding than DBA mice (high threshold) on the second day of life. Treatment with methylprednisolone acetate (MPA), a cyst-inducing steroid, down regulated dexamethasone binding earlier than in DBA mice. C3H mice demonstrated greater whole kidney homogenate Na-K ATPase activity than DBA mice within 24h of MPA injection. Specific renal glucocorticoid binding may be a regulator of threshold for murine glucocorticoid induced PKD. Our findings support in vitro evidence that glucocorticoid induced Na-K ATPase activity during critical periods of nephron development is an important regulatory point of this model.

Corticosterone regulation of type I and type II adrenal steroid receptors in brain, pituitary, and immune tissue

Type I and Type II adrenal steroid receptor levels were compared in the brain, pituitary and immune system of adrenalectomized rats in the presence or absence of several replacement doses of corticosterone. Six days of adrenalectomy produced an up-regulation of Type II adrenal steroid receptors in the brain and spleen. The lowest replacement dose of corticosterone (equivalent to resting levels of this hormone) blocked this Type II receptor up-regulation, while higher replacement doses of corticosterone were associated with widespread Type I and Type II adrenal steroid receptor down-regulation. However, the dose of corticosterone required for receptor down-regulation varied between tissues. Specifically, hippocampal receptors were most sensitive to corticosterone, whereas pituitary receptors were the least sensitive. All tissues examined, except the pituitary, exhibited a down-regulation of Type II receptors with a high corticosterone replacement dose which approximated acute stress levels of this hormone. In summary, physiologically relevant concentrations of corticosterone were capable of down-regulating Type I and Type II adrenal steroid receptors in multiple brain areas and peripheral immune tissues, including peripheral blood mononuclear cells. In contrast, adrenal steroid receptor levels in the pituitary were relatively insensitive to regulation by corticosterone.

Pharmacological characterization of type II glucocorticoid binding sites in AtT20 pituitary cell culture

Recent evidence indicates that at least two functional glucocorticoid receptors (Type I and Type II) are present in many tissues. It has also become increasingly recognized that, as in other systems, stimulus-response relationships for steroid hormones are often nonlinear. Thus, precise pharmacological parameters are required to establish a functional relationship(s) between binding site and response characteristics. We therefore pharmacologically characterized a glucocorticoid binding site present in AtT20 mouse pituitary cells, a cell line extensively used in studying Type II glucocorticoid receptor function. By several different criteria, glucocorticoids were shown to bind to a single class of binding sites, which, in comparison to available literature, correspond to classical Type II glucocorticoid receptors. No evidence for Type I adrenal steroid binding sites was observed, under the experimental conditions used. Unambiguous Kb values for both glucocorticoid agonists and antagonists were therefore calculated. These parameters should prove of use in elucidating the relationships between glucocorticoid receptor activation and different responses in both AtT20 cells and other glucocorticoid responsive tissues.

Characterization of Glucocorticoid Type II Receptors in Neuronal and Glial Cultures from Rat Brain

Abstract The purpose of this study was to characterize and compare the properties of glucocorticoid Type II receptors in neuronal and astrocyte glial cultures prepared from rat brain. Type II receptors in cytosol prepared from cultured cells were labeled with [(3) H]dexamethasone (DEX) at 0 degrees C. The binding was saturable and specific, with a complete displacement by unlabeled DEX or RU 28362 (a pure glucocorticoid). Scatchard analysis of [(3) H]DEX binding suggested a single class of receptors with a slightly lower dissociation constant (K(d)) in neuronal (1.13 nM) versus astrocyte glial (1.64 nM) cytosol. The number of binding sites (B(max)) in astrocyte glial cultures was four times that in neuronal cultures on a per milligram protein basis (120.3 versus 29.3 fmol/mg protein). The presence of Type II receptors in cultured neurons and astrocyte glia was further confirmed by immunofluorescent staining with a monoclonal antibody against this receptor (BuGR-2). The steroid specificity of Type II receptors was studied by examining the displacement of [(3) H]DEX binding to cytosol with unlabeled steroids. For both types of cultures, the potency series for competition was RU 28362> DEX> corticosterone> > aldosterone. Switching cultured cells from serum-supplemented to serum-free medium reduced [(3) H]DEX binding at low concentrations (0.5 to 5 nM) of the ligand in both types of culture, thus resulting in a decrease in the apparent affinity. This treatment did not, however, have any significant effect on the total number of binding sites. In summary, these results demonstrate that both neuronal and astrocyte glial cells in culture contain specific glucocorticoid Type II receptors, which resemble those seen in the brain and peripheral tissues.

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.

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.

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.

A novel effect of molybdate on the binding of [3H]aldosterone to gel-filtered type I receptors in brain cytosol

Recently we reported that adding molybdate to crude steroid-free cytosol at 0 degree C results in a dose-dependent reduction in the binding of [3H]aldosterone ([3H]ALDO) to Type I adrenocorticosteroid receptors. In the experiments outlined here, we found that addition of molybdate to steroid-free brain cytosol produces a 30-50% increase in the subsequently measured maximal specific binding capacity (BMAX) of [3H]ALDO-Type I receptors if the cytosol is subjected to Sephadex G-25 gel filtration prior to steroid addition. These manipulations were found to have no effect on the equilibrium dissociation constant (Kd) of the receptors. In contrast, when gel filtration of steroid-free cytosol was performed in the absence of molybdate, there was a 2-fold increase in the Kd and over a 50% reduction in the subsequently measured BMAX of [3H]ALDO-Type I receptors. When molybdate was added to this steroid-free cytosol immediately following gel filtration, there was no reduction (or increase) in Type I receptor [3H]ALDO binding capacity compared with non-gel-filtered controls. The addition of as little as 2 mM molybdate to crude steroid-free cytosol was found to stabilize the binding capacity of Type I receptors during exposure to 22 degrees C incubations; however, when gel-filtered steroid-free cytosol was exposed to these conditions at least 10 mM molybdate was required to stabilize Type I receptor binding capacity. Adding the sulfhydryl reducing reagent, dithiothreitol, to the various steroid-free cytosols had little effect on [3H]ALDO-Type I receptor binding.(ABSTRACT TRUNCATED AT 250 WORDS)

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

There are at least two classes of intracellular receptors for adrenocorticosteroid hormones in brain. Type I receptors have a high affinity for the naturally occurring gluco- and mineralocorticoids, corticosterone (CORT) and aldosterone (ALDO), respectively, and a very low affinity for synthetic glucocorticoids such as dexamethasone (DEX). type II receptors have a high affinity for the synthetic glucocorticoids, a lower affinity for CORT and a very low affinity for ALDO. In recent studies with mouse brain cytosol we have found a number of other biochemical differences between these two receptor types. In the present study, brain cytosol from adrenalectomized mice was prepared in HEPES buffer and subjected to various potentially inactivating treatments prior to assessment of Type I and Type II receptor specific binding capacity by incubation for 24 h at 0 degrees C with [3H]ALDO +/- [1H]RU 26988 (to prevent or permit the cross-binding of [3H]ALDO to Type II receptors) or [3H]DEX +/- [1H]Prorenone (to prevent or permit the cross-binding of [3H]DEX to Type I receptors), respectively. These studies revealed that 10-20% of the high-affinity (Kd = 3 nM) [3H]DEX specific binding capacity remained even after extensive, high concentration and repeated pretreatments with dextran-coated charcoal (DDC. to remove endogenous sulfhydryl-reducing reagents and other biochemicals). These procedures had little effect on Type I receptors. Further analyses revealed that DCC-resistant [3H]DEX binders were not Type I receptors since they were not saturated by [1H]Prorenone. These binders were also not inactivated by aging steroid-free cytosol at 0 degree C or by treating it with buffers containing 0.3 M KCl. Since these

Effects of polyhydric and monohydric compounds on the stability of type I receptors for adrenal steroids in brain cytosol

We have shown previously that unoccupied type I receptors for adrenal steroids in brain cytosol lose their capacity to bind [3H]aldosterone ([3H]ALDO) in a time- and temperature-dependent manner. Based on reports that sugars and polyvalent alcohols are capable of stabilizing a variety of globular proteins, we attempted in the present study to stabilize type I receptors by including polyhydric compounds in our brain cytosol preparations. However, contrary to expectations, adjusting cytosol to a 10% (g/dl) concentration of ethylene glycol, glycerol, erythritol, xylitol, ribitol, or sorbitol failed to stabilize these receptors at 0 degree C and in fact produced a slight reduction in [3H]ALDO binding capacity. The magnitude of this reduction was greater when cytosol was incubated for 2 h at 22 degrees C prior to incubation with [3H]ALDO. In contrast to these results, when brain cytosol was adjusted to a 10% (g/dl) concentration of the monohydric compound, ethanol, a significant increase in [3H]ALDO binding to type I receptors was found. Under identical conditions, methanol and propanol failed to have a significant effect on the binding capacity of these receptors. When cytosol was aged for 2 h at 22 degrees C, all three of these monohydric compounds produced a marked loss in the [3H]ALDO binding capacity of type I receptors. An investigation of various doses of ethanol at 0 degree C on the subsequent binding of [3H]ALDO yielded an inverse U-shaped curve with 10% ethanol producing the highest level of specific binding, as reflected by an increase in maximal binding in Scatchard plots, and 40% ethanol producing a complete loss in type I receptor binding capacity.(ABSTRACT TRUNCATED AT 250 WORDS)

Activated type II receptors in brain cannot rebind glucocorticoids: relationship to progesterone's antiglucocorticoid actions

Exchange assays have often been used to quantitate steroid receptors when endogenous ligands are present; however, there are no reports of their successful application to activated glucocorticoid-Type II receptor complexes. In addition to investigating the reasons for this failure, the present study also examined the effects of progesterone on glucocorticoid dissociation from, and reassociation with unactivated and activated Type II receptors. Molybdate-stabilized brain cytosol from adrenal-ovariectomized mice was incubated with [3H]dexamethasone ( +/- [1H]DEX) for 40 h at 0 degree C. Afterwards free steroid was removed on Sephadex G-25 columns in the presence (unactivated receptors) or absence (activated receptors) of molybdate. Activation, as measured by DNA-cellulose binding, was achieved by incubating molybdate-free cytosol at 22 degrees C for 20 min followed by G-25 filtration in the presence of molybdate. The rates of dissociation and reassociation were then measured by incubating cytosol with [1H]triamcinolone acetonide (TA) or [3H]TA ( +/- [1H]TA) at 12 degrees C. An exchange assay was also employed in which cytosol was incubated first with [1H]DEX for 40 h at 0 degree C followed by bound-free steroid separations and 12 degrees C incubations with [3H]TA ( +/- [1H]TA). Both approaches revealed that even though activation reduced the rate of DEX dissociation from Type II receptors by 40%, it eliminated the ability of the newly unoccupied receptors to rebind glucocorticoid. Adding [1H]progesterone to occupied receptor preparations increased dissociation rate constants by nearly 3-fold, for both unactivated and activated Type II receptors. Since [1H]TA failed to prevent this effect, progesterone appears to act at an allosteric site(s) which cannot be occupied by glucocorticoids. Exchange assays revealed that progesterone-facilitated dissociation increased the rate of glucocorticoid rebinding to unactivated, but not activated Type II receptors. These results suggest that spontaneous and progesterone-facilitated termination of glucocorticoid genomic actions could be mediated by steroid dissociation since unoccupied activated Type II receptors do not rebind agonist steroid.

Transformation of the [3H]aldosterone-type I receptor complex to a DNA-binding species

For most steroid receptor complexes, the transformation to a DNA-binding species can be achieved readily in vitro by incubation at elevated temperatures and/or salt concentrations. Although the aldosterone-Type I receptor complex forms a clear exception to this generalization, a marked increase in its transformation can be achieved by incubation with the chaotropic anion, thiocyanate. Time and concentration-response analyses with brain cytosol revealed that over 40% of the complexes were retained in DNA-cellulose assays after a 15 min pre-incubation at 0 degree C with 100 mM thiocyanate. As expected, molybdate prevented this transformation; however, in contrast to results with heat- and/or salt-induced transformation of other steroid receptors, the molybdate effect was only partially removed by gel filtering the cytosol prior to thiocyanate addition. Thiocyanate-induced transformation should prove useful in the biochemical characterization and purification of non-transformed and transformed aldosterone-Type I receptor complexes.

Functions and dysfunctions of receptors for adrenal corticoids in the central nervous system

Glucocorticoids (GC) have several known effects on the function of the nervous system, and GC receptors have been identified in regions responding to hormonal action. In the spinal cord, GC receptors have been characterized in vitro, which share several biochemical properties in common with receptors in better studied areas such as the hippocampus. Moreover, enzymes which are induced by GC in the hippocampus, such as glycerolphosphate dehydrogenase and ornithine decarboxylase, are also under specific GC control in the spinal cord. Yet GC receptors in the latter tissue divert from those in hippocampus during some in vivo as well as in vitro studies. In vivo, uptake of [3H]corticosterone by purified cell nuclei was 5-8-fold higher in the hippocampus as compared to the cord. In vitro, a higher percentage of GC receptors previously transformed by heating, showed affinity towards DNA-cellulose in the spinal cord than in the hippocampus. The enzyme RNAse A effectively increased receptor binding to DNA-cellulose in hippocampus, whereas the cord was insensitive to its action. These results suggest that there is a "receptor dysfunction" in the spinal cord, the significance of which is poorly understood in terms of the accepted model of steroid hormone action.

Chemical differentiation of type I and type II receptors for adrenal steroids in brain cytosol

Studies outlined here compare the properties of mineralocorticoid (Type I) and glucocorticoid (Type II) receptors in cytosol from adrenalectomized mouse brain. Pretreating cytosol with dextran-coated charcoal (DCC) produced a 4.7-fold increase in the subsequent macromolecular binding of the mineralocorticoid, [3H]aldosterone (20 nM ALDO, in the presence of a 50-fold molar excess of the highly specific synthetic glucocorticoid, RU 26988), whereas it produced a 55% decrease in the binding of the glucocorticoid, [3H]triamcinolone acetonide (20 nM TA). Scatchard analyses revealed that DCC pretreatment had no effect on the affinity or maximal binding of Type I receptors for [3H]ALDO (in the presence of a 0-, 50- or 500-fold excess of RU 26988), whereas it produced a 3- to 6-fold increase in the Kd, and an 8-43% decrease in the maximal binding, of Type II receptors for [3H]TA and [3H]dexamethasone. Optimal stability of unoccupied Type I receptors at 0 degree C was found to be achieved in buffers containing glycerol, but lacking molybdate. Although the addition of molybdate was found to reduce the loss in Type I receptor binding observed after incubating unlabelled cytosol at 12 or 22 degrees C, this stabilization was accompanied by a concentration-dependent reduction in the binding of [3H]ALDO at 0 degree C. Scatchard analyses showed that this reduction was due to a shift in the maximal binding, and not the affinity, of the Type I receptors for [3H]ALDO. The presence or absence of dithiothreitol in cytosol appeared to have little effect on the stability of Type I receptors. In contrast to our finding for Type I receptors, it was possible to stabilize the binding capacity of unoccupied Type II receptors, even after 2-4 h at 12 or 22 degrees C, if the glycerol containing buffers were supplemented with both molybdate and dithiothreitol. In summary, these results indicate distinct chemical differences between Type I and Type II receptors for adrenal steroids.