Physiological Concentrations Of Corticosterone Research Articles

11βHSD2 Efficacy in Preventing Transcriptional Activation of the Mineralocorticoid Receptor by Corticosterone.

Affinity of the mineralocorticoid receptor (MR) is similar for aldosterone and the glucocorticoids (GC) cortisol and corticosterone, which circulate at concentrations far exceeding those of aldosterone. 11β-hydroxysteroid dehydrogenase type 2 (11βHSD2) inactivation of GC within the immediate vicinity of the MR is credited with prereceptor specificity for aldosterone in cells coexpressing MR and 11βHSD2. 11βHSD2 efficacy is also critical to other recently described 11βHSD2 substrates. The aim of this work was to address doubts that low levels of expression of 11βHSD2 in aldosterone target tissues suffice to prevent the initiation of gene transcription by the MR activated by physiological concentrations of corticosterone. Cell models stably expressing an MR/Gaussia luciferase reporter and various levels of constitutive or induced 11βHSD2 at concentrations lower than those in rat kidney homogenates and microsomes were produced. Aldosterone and corticosterone were equipotent transactivators of the MR reporter gene in cells without 11βHSD2. Rate of conversion of tritiated corticosterone to 11-dehydrocorticosterone increased and corticosterone-induced nuclear translocation of MR decreased, as 11βHSD2 expression increased. The 50% maximal MR activation for the reporter gene stimulation by corticosterone rose with increasing 11βHSD2 expression, shifting the steroid dose-response curve for corticosterone-induced MR transactivation to the right. Several stable cell lines expressing an easily and reproducibly measured MR reporter system and consistent incremental amounts of 11βHSD2 protein were produced and used to document that 11βHSD2 within low physiological levels inactivates relevant concentrations of GC and decreases MR transactivation by GC in a dose-dependent fashion, laying to rest doubts of the efficacy of this enzyme.

Autogenous transplants of adrenal fragments in an animal model.

Autograft transplantation was performed on 3 groups of Sprague Dawley rats. In the first group, physiological corticosterone concentrations were determined. These animals were not operated. In the second group, both adrenal glands were removed. Corticosterone concentrations were determined after bilateral adrenalectomy. The third group was divided into two parts. In the first subgroup, bilateral adrenalectomy was performed simultaneosly with adrenal transplant into the omentum. In the second subgroup, right adrenalectomy was performed simultaneosly with and adrenal transplant into the omentum followed a month later by left adrenalectomy. During the experiment, corticosterone concentrations were measured at 4 time points. The statistical difference between corticosterone concentrations in rats after two timed adrenalectomies and rats after bilateral adrenalectomy was statistically different, but these results were far from physiological concentrations.

Thymus-derived glucocorticoids are insufficient for normal thymus homeostasis in the adult mouse

BackgroundIt is unclear if thymus-derived glucocorticoids reach sufficient local concentrations to support normal thymus homeostasis, or if adrenal-derived glucocorticoids from the circulation are required. Modern approaches to this issue (transgenic mice that under or over express glucocorticoid receptor in the thymus) have yielded irreconcilably contradictory results, suggesting fundamental problems with one or more the transgenic mouse strains used. In the present study, a more direct approach was used, in which mice were adrenalectomized with or without restoration of circulating corticosterone using timed release pellets. Reversal of the increased number of thymocytes caused by adrenalectomy following restoration of physiological corticosterone concentrations would indicate that corticosterone is the major adrenal product involved in thymic homeostasis.ResultsA clear relationship was observed between systemic corticosterone concentration, thymus cell number, and percentage of apoptotic thymocytes. Physiological concentrations of corticosterone in adrenalectomized mice restored thymus cell number to normal values and revealed differential sensitivity of thymocyte subpopulations to physiological and stress-inducible corticosterone concentrations.ConclusionThis indicates that thymus-derived glucocorticoids are not sufficient to maintain normal levels of death by neglect in the thymus, but that apoptosis and possibly other mechanisms induced by physiological, non stress-induced levels of adrenal-derived corticosterone are responsible for keeping the total number of thymocytes within the normal range.

Myocardial IL-6 regulation by neurohormones—an in vitro superfusion study

Background: Interleukin-6 (IL-6) is expressed in the myocardium and has been implicated in cell proliferation, negative inotropic effects and myocardial hypertrophy. To determine whether myocardial IL-6 is modified by neurohumoral and immunoregulatory stimuli, we studied the effects of lipopolysaccharide (LPS), corticosterone (CS), isoproterenol and angiotensin II on myocardial IL-6 secretion in superfused myocardium. Methods: Slices of rat left ventricular myocardium were superfused in 80 μl chambers for up to 5 h. LPS (1, 50, and 100 μg/ml), CS (10 −7, 10 −6, and 10 −5 M, DSMO as vehicle), isoproterenol (10 −6, 10 −7, and 10 −8 M) and angiotensin II (10 −5, 10 −7, and 10 −9 M) were added to the culture medium at hour 2. IL-6 was measured in the perfusate by ELISA. Results: Physiological corticosterone concentrations (10 −7 M) resulted in an increase in IL-6 concentration (142%) while high doses of steroid decreased IL-6 significantly (CS 10 −6 M: 88±14%, p<.05 ; CS 10 −5: 91±9%, p<.05 ) after 5 h. Left ventricular IL-6 secretion was significantly stimulated by LPS 50 μg/ml (3262±1684% vs. CTRL: 116±34%, p<.01). Isoproterenol treatment increased in IL-6 secretion compared to controls with and without CS, while angiotensin II reduced IL-6 concentration only in combination with CS. Conclusion: Myocardial IL-6 secretion is modulated by physiological concentrations of corticosterone or angiotensin II and can be induced by LPS or isoproterenol, indicating a tight regulation of this cytokine. Suppression of cytokine expression within the heart might be a potential therapeutic goal in the treatment of various cardiovascular diseases.

Steroid modulation of GABA A receptors in an amphibian brain

Steroids can modulate γ-aminobutyric acid (GABA A) receptor function in rat brains, but the physiological relevance of this mechanism is still unclear. To determine whether this phenomenon is widespread among vertebrates, we investigated steroid modulation of GABA A receptors in amphibian brain tissue. Equilibrium binding parameters for t-butylbicyclophosphorothionate ([ 35S]TBPS) and [ 3H]flunitrazepam were similar in Tricha glanulosa and mammalian brains, as was the allosteric regulation of [ 35S]TBPS and [ 3H]flunitrazepam binding in GABA. The rank order and absolute potencies of steroids to inhibit [ 35S]TBPS binding and enhance [ 3H]flunitrazepam binding were also similar in Taricha and rat brains. As in mammalian studies, physiological concentrations of corticosterone had no effect on ligand binding of GABA-stimulated Cl − uptake. In autoradiogrphic studies, 3α-hydroxy-5α-pregnan-20-one inhibited [ 35S]TBPS binding sites in all brain regions examined, whereas corticosterone had no effect on [ 35S]TBPS binding. These studies suggest that the steroid recognition sites on GABA A receptors bave been highly conserved through vertebrate evolution and thus portend physiologically important functions. However, the pharmacological profiles for the GABA A receptor and high-affinity coritcosteroid receptor are apparently different, suggesting there are multiple types of steroid recognition sites on neuronal membranes.

Corticosterone Enhances the Zinc and Interleukin-6-Mediated Induction of Metallothionein in Cultured Rat Hepatocytes

The regulation of metallothionein induction in cultured rat hepatocytes was investigated with Zn, hormones, cytokines and either the synthetic glucocorticoid, dexamethasone, or the endogenous rat glucocorticoid, corticosterone. A concentration-dependent increase was seen with Zn (two- to fivefold increase in 24 h, Zn 10-50 mumol/L). Dexamethasone at 1 mumol/L increased metallothionein synthesis by fourfold that of the controls. Maximal metallothionein concentrations of 17-fold the control value were seen with 50 mumol/L Zn and 1 mumol/L dexamethasone. Interleukin-6 (1 x 10(5) U/L) alone did not induce metallothionein but increased it 35-65% with Zn+dexamethasone. Like dexamethasone, corticosterone had a dose dependent effect on metallothionein and synergy with Zn and Zn+interleukin-6. Dexamethasone was approximately 100 times more potent than corticosterone at 10-100 mumol/L. Physiological concentrations of corticosterone (1 mumol/L) when added alone, with Zn (10 mumol/L), and with Zn+interleukin-6 resulted in inductions of 2.2, 5.0 and 7.4-fold above the control cultures. Glucagon (1 mumol/L) had no independent effect but increased metallothionein by 31% and 33% with Zn(10 mumol/L)+dexamethasone (1 mumol/L) and Zn-dexamethasone+interleukin-6, respectively. There was no accumulation of metallothionein with interleukin-1 beta, tumor necrosis factor alpha or interferon gamma (1 x 10(5) U/L) alone, but interleukin-1 beta and tumor necrosis factor alpha enhanced the response obtained with Zn+dexamethasone with and without interleukin-6. Insulin (100 U/L) alone, caused metallothionein accumulation and further enhanced the response seen with Zn+dexamethasone+interleukin-6+glucagon. No additional enhancement was seen with interleukin 1 beta+tumor necrosis factor alpha+interferon. The results demonstrate that concentrations of corticosterone in rats with experimental inflammation facilitate metallothionein induction with Zn and interleukin-6.(ABSTRACT TRUNCATED AT 250 WORDS)

Corticosterone exacerbates kainate-induced alterations in hippocampal tau immunoreactivity and spectrin proteolysis in vivo.

Aberrant elevations in intracellular calcium levels, promoted by the excitatory amino acid glutamate, may be a final common mediator of the neuronal damage that occurs in hypoxic-ischemic and seizure disorders. Glutamate and altered neuronal calcium homeostasis have also been proposed to play roles in more chronic neurodegenerative disorders, including Alzheimer's disease. Any extrinsic factors that may augment calcium levels during such disorders may significantly exacerbate the resulting damage. Glucocorticoids (GCs), the adrenal steroid hormones released during stress, may represent one such extrinsic factor. GCs can exacerbate hippocampal damage induced by excitotoxic seizures and hypoxia-ischemia, and we have observed recently that GCs elevate intracellular calcium levels in hippocampal neurons. We now report that the excitotoxin kainic acid (KA) can elicit antigenic changes in the microtubule-associated protein tau similar to those seen in the neurofibrillary tangles of Alzheimer's disease. KA induced a transient increase in the immunoreactivity of hippocampal CA3 neurons towards antibodies that recognize aberrant forms of tau (5E2 and Alz-50). The tau immunoreactivity appeared within 3 h of KA injection, preceded extensive neuronal damage, and subsequently disappeared as neurons degenerated. KA also caused spectrin breakdown, indicating the involvement of calcium-dependent proteases. Physiological concentrations of corticosterone (the species-typical GC of rats) enhanced the neuronal damage induced by KA and, critically, enhanced the intensity of tau immunoreactivity and spectrin breakdown. Moreover, the GC enhancement of spectrin proteolysis was prevented by energy supplementation, supporting the hypothesis that GC disruption of calcium homeostasis in the hippocampus is energetic in nature. Taken together, these findings demonstrate that neurofibrillary tangle-like alterations in tau, and spectrin breakdown, can be induced by excitatory amino acids and exacerbated by GCs in vivo.

Hypocalcemic Effect of Physiological Concentrations of Corticosterone in Adrenalectomized-Parathyroidectomized Rats*

We have confirmed the serum calcium-raising effect of adrenalectomy in young male rats 5-6 h after parathyroidectomy that was first observed by others many years ago. (The phenomenon has also been reported in cats, dogs, and mice.) In addition, we have shown that adrenalectomy raises the serum ionized calcium as well as total calcium and that the effect occurs in young female as well as in young male rats. Furthermore, we have found that the serum calcium-raising effect of adrenalectomy occurs if the adrenalectomy is performed several days before parathyroidectomy or 6 h after parathyroidectomy, as well as at the same time as the parathyroidectomy. When the rats were adrenalectomized 7-9 days before parathyroidectomy and given small daily life-maintaining doses of corticosterone or cortisone acetate, this glucocorticoid treatment did not reverse the adrenalectomy effect. This led us to think at first that the effect of adrenalectomy must be due to the loss of an unknown adrenal factor rather than to loss of glucocorticoid. Additional experiments, however, in which corticosterone or hydrocortisone was administered by continuous release pellets, demonstrated conclusively that a small continuous supply of corticosterone (within the physiological range as determined by immunoassay of plasma) was sufficient to reverse the adrenalectomy effect. The results with hydrocortisone were similar at even lower doses than of corticosterone. Somewhat higher doses of corticosterone or hydrocortisone reduced the serum calcium even below the parathyroidectomy level. In a preliminary investigation of the specificity of the glucocorticoid effect we found that aldosterone, dehydroepiandrosterone, or estradiol had no effect on serum calcium under similar conditions. We conclude that the fall in serum calcium after parathyroidectomy in rats is due in part to the hypocalcemic effect of endogenous corticosterone. Thus, the loss of corticosterone after adrenalectomy explains the serum calcium-raising effect of adrenalectomy in parathyroidectomized rats. These results also suggest that glucocorticoids at physiological levels have a significant effect on calcium metabolism in general.

Glucocorticoids decrease in conversion of thyroxine into 3, 5, 3'-tri-iodothyronine by isolated rat renal tubules.

1. The effect of glucocorticoids on the deiodination of thyroxine (T4) to 3,5,3'-tri-iodothyronine (T3) was studied in rat renal tubules prepared by collagenase digestion. 2. In short-term (6h) experiments, cortisol and dexamethasone inhibited the conversion of T4 into T3 at concentrations of 2 X 10-4 mol/l and 2 X 10-5 mol/l respectively. The inhibition by cortisol and dexamethasone was time dependent and was prevented by actinomycin D and progesterone, suggesting that the inhibition is mediated by an effect on nuclear transcription dependent on binding to glucocorticoid receptors. 3. In long-term (16 h) experiments, cortisol and dexamethasone inhibited T4 to T3 conversion by the tubules at concentrations of 1 X 10-12 mol/l and above. In addition, physiological concentrations of corticosterone (1 X 10-8 mol/l) were able to decrease T3 generation from T4. 4. Our data provide strong evidence that physiological concentrations of glucocorticoids are able to affect T3 production from T4 directly and suggest that they may be important regulators of T4 deiodination.U