High Dose Of Dex Research Articles

Induction of CYP3A activity by dexamethasone may not be strong, even at high doses: insights from a case of tacrolimus co-administration

BackgroundDexamethasone (DEX) induces CYP3A activity in a concentration-dependent manner. However, no study has examined changes in the blood concentration of CYP3A substrate drugs when DEX is administered at high doses. Herein, we present a case in which tacrolimus (TAC), a typical CYP3A substrate drug, was co-administered with a chemotherapy regimen that included high-dose DEX.Case presentationA 71-year-old woman underwent liver transplantation for hepatocellular carcinoma 18 years prior to her inclusion in this case study. She was receiving TAC orally at 2 mg/day and had a stable trough blood concentration of approximately 4 ng/mL and a trough blood concentration/dose (C/D) ratio of approximately 2. The patient was diagnosed with post-transplant lymphoproliferative disease (histological type: Burkitt's lymphoma) after admission. Thereafter, the patient received cyclophosphamide-prednisolone (CP), followed by two courses of R-HyperCVAD (rituximab, cyclophosphamide, doxorubicin, vincristine, and DEX) and R-MA (rituximab, methotrexate, and cytarabine) replacement therapy. DEX (33 mg/day) was administered intravenously on days 1–4 and days 11–14 of R-HyperCVAD treatment, and aprepitant (APR) was administered on days 1–5 in both courses. The TAC C/D ratio decreased to approximately 1 on day 11 during both courses, and then increased. Furthermore, a decreasing trend in the TAC C/D ratio was observed after R-MA therapy. The decrease in the TAC C/D ratio was attributed to APR administration rather than to DEX.ConclusionThe induction of CYP3A activity by a high dose of DEX may not be strong. The pharmacokinetic information on DEX and in vitro enzyme activity induction studies also suggested that CYP3A activity induction is not prominent under high-dose DEX treatment.

Tailored Therapeutic Doses of Dexmedetomidine in Evolving Neuroinflammation after Traumatic Brain Injury.

Understanding the secondary damage mechanisms of traumatic brain injury (TBI) is essential for developing new therapeutic approaches. Neuroinflammation has a pivotal role in secondary brain injury after TBI. Activation of NLRP3 inflammasome complexes results in the secretion of proinflammatory mediators and, in addition, later in the response, microglial activation and migration of the peripheral immune cells into the injured brain are observed. Therefore, these components involved in the inflammatory process are becoming a new treatment target in TBI. Dexmedetomidine (Dex) is an effective drug, widely used over the past few years in neurocritical care units and during surgical operations for sedation and analgesia, and has anti-inflammatory effects, which are shown in in vivo studies. The aim of this original research is to discuss the anti-inflammatory effects of different Dex doses over time in TBI. Brain injury was performed by using a weight-drop model. Half an hour after the trauma, intraperitoneal saline was injected into the control groups and 40 and 200μg/kg of Dex were given to the drug groups. Neurological evaluations were performed with the modified Neurological Severity Score before being killed. Then, the mice were killed on the first or the third day after TBI and histopathologic (hematoxylin-eosin) and immunofluorescent (Iba1, NLRP3, interleukin-1β, and CD3) findings of the brain tissues were examined. Nonparametric data were analyzed by using the Kruskal-Wallis test for multiple comparisons, and the Mann-Whitney U-test was done for comparing two groups. The results are presented as mean ± standard error of mean. The results showed that low doses of Dex suppress NLRP3 and interleukin-1β in both terms. Additionally, high doses of Dex cause a remarkable decrease in the migration and motility of microglial cells and T cells in the late phase following TBI. Interestingly, the immune cells were influenced by only high-dose Dex in the late phase of TBI and it also improves neurologic outcome in the same period. In the mice head trauma model, different doses of Dex attenuate neuroinflammation by suppressing distinct components of the neuroinflammatory process in a different timecourse that contributes to neurologic recovery. These results suggest that Dex may be an appropriate choice for sedation and analgesia in patients with TBI.

Dexamethasone-Induced Liver Enlargement Is Related to PXR/YAP Activation and Lipid Accumulation but Not Hepatocyte Proliferation.

Dexamethasone (Dex), a widely prescribed anti-inflammatory drug, was reported to induce liver enlargement (hepatomegaly) in clinical practice and in animal models. However, the underlying mechanisms are not elucidated. Dex is a known activator of pregnane X receptor (PXR). Yes-associated protein (YAP) has been implicated in chemically induced liver enlargement. Here, the roles of PXR and YAP pathways were investigated in Dex-induced hepatomegaly. Upregulation of PXR downstream proteins, including cytochrome P450 (CYP) 3A11, 2B10, and organic anion transporter polypeptide 2 (OATP2), indicated PXR signaling was activated after high dose of Dex (50 mg/kg, i.p.), and Dex at 100 μM activated PXR in the dual-luciferase reporter gene assay. Dex also increased the expression of total YAP, nuclear YAP, and YAP downstream proteins, including connective tissue growth factor and cysteine-rich angiogenic inducer 61, indicating activation of the YAP pathway. Furthermore, nuclear translocation of YAP was promoted by activation of PXR. However, hepatocyte proliferation was inhibited with significant decrease in the expression of proliferation-related proteins cyclin D1 and proliferating cell nuclear antigen as well as other regulatory factors, such as forkhead box protein M1, c-MYC, and epidermal growth factor receptor. The inhibitory effect of Dex on hepatocyte proliferation was likely due to its anti-inflammation effect of suppression of inflammation factors. β-catenin staining revealed enlarged hepatocytes, which were mostly attributable to the accumulation of lipids, such as triglycerides. In summary, high-dose Dex increased liver size accompanied by enlarged hepatocytes, and this was due to the activation of PXR/YAP and their effects on lipid accumulation but not hepatocyte proliferation. These findings provide new insights for understanding the mechanism of Dex-induced hepatomegaly. SIGNIFICANCE STATEMENT: This study identified the roles of pregnane X receptor (PXR) and yes-associated protein (YAP) pathways in dexamethasone (Dex)-induced hepatomegaly. Dex induced PXR/YAP activation, enlarged hepatocytes, and promoted liver enlargement with lipid accumulation, such as triglycerides. However, hepatocyte proliferation was inhibited by the anti-inflammatory effect of Dex. These findings provide new insights for understanding the mechanism of Dex-induced hepatomegaly.

Low-dose dexamethasone affects osteoblast viability by inducing autophagy via intracellular ROS.

Glucocorticoids (GCs) are closely associated with the progression of GC-induced osteoporosis (GIOP) by inhibiting osteoblast viability. However, endogenous GCs are important for bone development. In addition, previous studies have demonstrated that GCs could induce autophagy, a cytoprotective process that is protective against various stressors. In the present study, the aim is to explore whether osteoblasts exhibited dose-dependent viability in the presence of GCs due to autophagy. hFOB 1.19 osteoblasts were treated with various doses of dexamethasone (DEX; 10−8-10−4 M) for 0, 24, 48 and 72 h. The results revealed a biphasic effect of DEX on the viability of hFOB 1.19 cells; a high dose of DEX (≥10−6 M) accelerated cell apoptosis, while a low dose of DEX (10−8 M) increased cell viability. Furthermore, significantly increased autophagy was observed in the low dose DEX treatment group, as indicated by the expression of the autophagy-associated proteins beclin 1 and microtubule-associated protein light chain 3, and the detection of autophagosomes. Another finding was that DEX upregulated intracellular reactive oxygen species (ROS), which was decreased by the autophagy agonist rapamycin. The increase in autophagy and cell viability associated with low-dose DEX (10−8 M) was suppressed by the ROS scavenger catalase and the autophagy inhibitor 3-methyladenine. In conclusion, the results revealed that GCs affected osteoblast viability in a dose-dependent manner. A low dose of GCs increased osteoblast viability by inducing autophagy via intracellular ROS. The results indicate that autophagy may be a novel mechanism by which osteoblasts survive GC exposure and provide a potential therapeutic target for treating GIOP.

The expression changes of norepinephrine, acetylcholine, muscarinic receptors-2, adenosine receptors-1 on sinus bradycardia model caused by dexmedetomidine in rabbits

Objective To investigate the effects of dexmedetomidine(Dex) on norepinephrine(NE), acetylcholine(Ach), muscarinic receptors 2(M2), adenosine receptors 1(A1) of rabbits, and to clarify the mechanism of dex-induced bradyarrhythmias. Methods Twenty four healthy male rabbits were randomly divided into 3 groups(n=8), including control(group C), low dose of Dex (group D1), and high dose of Dex(group D2). Rabbits were administered normal saline in group C. Rats in group D1 were administered Dex at loading dose of 10 μg/kg for 10 min, and then at 5 μg·kg-1·h-1 for 50 min. Rats in group D2 were administered with Dex at loading dose of 60 μg/kg for 10 min and then at 30 μg·kg-1·h-1 for 50 min. After rabbits were anesthesia by sodium pentobarbital, basic operations were quickly were completed in order to measure MAP and ECG. HR, MAP were obtained before(T0), 15 min after (T1), 30 min after(T2), 60 min after(T3) intravenous pumping of Dex. After observation of Dex pump injection, hearts were quickly removed and divided accurately the sinus node. The experiment indicators were detected by the Real-time quantitative PCR, Immunohistochemical, ELISA. Results There was no significant difference in HR and MAP at T0 among the three groups(P>0.05). Compared with group C,HR, MAP were decreased at T1, T2, T3 in group D1, D2(P 0.05). Relative gene expression of A1 in group D2 significantly increased than group C[(13±5) vs (5±3)], D1[(13±5) vs (6±4)](P 0.05). Ach in group D2 were significantly increased than group C, D1(P<0.05). Conclusions Dex decreases NE of sympathetic transmitter and Ach vagus nerve neurotransmitter of only increases significantly in the high-dose group. High dose of Dex directly increasing vagus nerve activities. M2, A1 in the high-dose group showed a trend of rise significantly. Key words: Dexmedetomidine; Sinus bradycardia; Sinuatrial node; Norepinephrine; Acetylcholine; Muscarinic receptors-2; Adenosine receptors-1; Rabbits

Effects of dexmedetomidine on baroreflex sensitivity of rabbits

Objective To investigate the effects of dexmedetomidine(Dex) on baroreflex sensitivit(BRS) of rabbits, and evaluate the effects of Dex on the tension of vagus nerve. Methods Twenty four healthy male rabbits were randomly divided into 3 groups(n=8), including group C(control), group D1(low dose of Dex), and group D2(high dose of Dex). Rabbits were administered with Dex normal saline in group C, they were administered with Dex at loading dose of 10 μg/kg, and then pumped with Dex at 5 μg·kg-1·h-1 in group D1, they were administered with Dex at loading dose of 60 μg/kg and then at 30 μg · kg-1·h-1 in group D2. The values of BRS was measured before(T0), 30 min after(T1) and 60 min after(T2) intravenous pumping of Dex. Results The values of BRS at T1, T2 in group D1 and D2 incareased compared with T0(P<0.05), The values of BRS at T2 in group D1 decreased significantly compared with T1(P< 0.05). The values of BRS in group D1 and D2 were significantly increased than group C at T1, T2(P<0.05). The values of BRS in group D2 were significantly increased than group D1 at T1, T2(P<0.05). Conclusions Dex can increase BRS of rabbits, with increasing of Dex concentration of BRS increased effect are more significant and persistent, also which reflects the Dex can increase the vagus nerve tension in dose-dependent manner. Key words: Rabbits; Dexmedetomidine; Baroreflex sensitivity; Vagus nerve tension

Abstract A56: Regulation of breast tumor kinase (Brk) expression in triple-negative breast cancer integrates cellular (HIF-2alpha) and hormonal (cortisol) stress signaling

Abstract Triple-negative breast cancers (TNBC) have a worse prognosis relative to other breast cancer subtypes, underscoring the urgent need for identification of driver molecules or pathways for targeted therapies. Breast tumor kinase (Brk) is a soluble tyrosine kinase that is aberrantly elevated and active in 86% of breast cancers. Our lab has shown Brk to be a potent driver of basal-type mammary tumors. Mechanisms through which Brk overexpression is acquired in breast cancer cells are largely unknown. We recently reported that Brk is a direct target gene of hypoxia-inducible factor 1 alpha (HIF-1alpha) and HIF-2alpha, activated in response to cellular stresses such as hypoxia, low glucose, or nutrient starvation. It is becoming increasingly evident that the stress sensing hormone, cortisol, via activation of the glucocorticoid receptor (GR), leads to cell survival and chemoresistance in tumors of epithelial origin, such as breast cancer. In fact, GR expression in TNBC predicts poor outcome. Herein, we sought to investigate crosstalk between cell stress pathways and GR signaling that may influence expression of Brk in TNBC. An explant model of primary human TNBC demonstrated robust induction of Brk mRNA and protein with the GR ligand, dexamethasone (dex). Brk mRNA and protein were also induced in response to dex in TNBC cell line models. MDA-MB-231 cells with HIF-1a/2a knockdown (DKD), failed to induce Brk expression following dex treatment, suggesting that GR regulation of Brk requires HIF-1a/2a. Chromatin immunoprecipitation (ChIP) assays showed HIF and GR co-recruitment to the Brk promoter in response to either hypoxia or dex, indicating that Brk is a direct GR/HIF target gene. HIF-2a mRNA and protein were also directly regulated by GR in response to dex treatment. Notably, expression of Proline, glutamate and leucine rich protein 1 (PELP1), an important steroid receptor coactivator, was significantly induced by hypoxic cell stress, while DKD cells (lacking HIFs) exhibited markedly reduced PELP1 protein levels relative to control cells. Co-immunoprecipitation (co-IP) assays showed that PELP1 and GR interact basally and in response to dex treatment in multiple TNBC cell lines. Moreover, PELP1 was recruited to the Brk promoter with HIF2a and GR following dex treatment. Inhibition of PELP1 with the peptidomemtic, D2, blocked dex induction of Brk mRNA. Physiologic cell stress resulted in phosphorylation of GR at serine 134 (S134) and this event was required for the GR and PELP1 interaction. Enhanced phosphorylation at this site via H2O2 treatment increased GR recruitment to the Brk promoter, while blockade of this site via the p38 MAPK inhibitor SB203580 diminished GR recruitment to the Brk promoter and blocked Brk induction. Notably, mutant GR in which S134 was mutated to an alanine (S134A) was not recruited to the Brk promoter basally or in response to dex treatment, highlighting the importance of this phosphorylation event in the GR regulation of Brk expression. Our data show that GR initiates a feed-forward signaling loop leading to upregulation of Brk in TNBC and reveal molecular linkage between cell stress and stress hormone signaling in driving aggressive phenotypes in breast cancer. Collectively, our studies suggest that GR, HIF, PELP1 cross talk may promote aggressive tumor behavior, in part via upregulation of Brk. Breast cancer patients are routinely given high doses of dex to alleviate the inflammatory side effects of chemotherapy. This treatment may inadvertently promote chemoresistance and tumor progression via robust induction of Brk expression. Targeting the GR/HIF/PELP1 complex may provide a means of blocking Brk-dependent tumor progression and metastasis in patients with TNBC. Citation Format: Tarah M. Regan Anderson, Shihong Ma, Ganesh V. Raj, Carol A. Lange. Regulation of breast tumor kinase (Brk) expression in triple-negative breast cancer integrates cellular (HIF-2alpha) and hormonal (cortisol) stress signaling. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research; Oct 17-20, 2015; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(2_Suppl):Abstract nr A56.

The Glucocorticoid Dexamethasone Inhibits U937 Cell Adhesion and Neutrophil Release via RhoA/ROCK1-Dependent and Independent Pathways

Aims: The aim of the present study was to investigate the role of the Ras homolog family member A (RhoA)/Rho-associated coiled-coil-containing protein kinase 1 (ROCK1) signaling pathway in the inhibition of inflammatory responses by the glucocorticoid dexamethasone (Dex). Methods: The inhibitory effects of Dex and Rho-kinase inhibitor fasudil (Fas) on phorbol ester-induced release of O₂^- and MPO from neutrophils and on U937 mononuclear cell adhesion were examined along with the expression and activity levels of RhoA and ROCK1. Results: High doses of Dex rapidly inhibited the release of O₂^- and myeloperoxidase (MPO) from neutrophils and the adhesion of U937 cells, while Fas was only found to inhibit U937 cell adhesion. Additionally, Dex suppressed ROCK1 activity. However, Dex had no effects on ROCK1 or RhoA expression levels or on RhoA activity. Neither the glucocorticoid receptor antagonist mifepristone (RU-486) nor the protein synthesis inhibitor cycloheximide (CHX) was able to suppress the effects of Dex (p>0.05). Conclusions: The present findings indicate that Dex suppressed neutrophil release through ROCK1-independent mechanisms and inhibited the adhesion of U937 mononuclear cells through ROCK1-dependent non-genomic mechanisms that did not involve RhoA.

Low Doses of Dexamethasone Can Produce a Hypocorticosteroid State in the Brain

The synthetic glucocorticoid dexamethasone (dex) blocks stress-induced hypothalamic-pituitary-adrenal (HPA) activation primarily at the level of the anterior pituitary because multidrug resistance P-glycoprotein hampers its penetration in the brain. Here, we tested the hypothesis that central components of the HPA axis would escape dex suppression under conditions of potent peripheral glucocorticoid action. We subchronically treated rats with low or high doses of dex. The animals were subjected on the last day of treatment for 30 min to a restraint stressor after which central and peripheral markers of HPA axis activity were measured. Basal and stress-induced corticosterone secretion, body weight gain, adrenal and thymus weight, as well as proopiomelanocortin mRNA in the anterior pituitary were reduced in a dose-dependent manner by dex administered either 5 d sc or 3 wk orally. In the brain, the highest dose dex suppressed CRH mRNA and CRH heteronuclear RNA in the paraventricular nucleus (PVN). However, in the peripherally active low-dose range of dex CRH mRNA and heteronuclear RNA showed resistance to suppression, and CRH mRNA expression in the PVN was in fact enhanced under the long-term treatment condition. In the PVN, c-fos mRNA was suppressed by the highest dose of dex, but this effect showed a degree of resistance after long-term oral treatment. c-fos mRNA responses in the anterior pituitary followed those in PVN and reflect central drive of the HPA axis even if corticosterone responses are strongly reduced. The results support the concept that low doses of dex can create a hypocorticoid state in the brain.

Glucocorticoid receptors, in vitro steroid sensitivity, and cytokine secretion in idiopathic nephrotic syndrome

Glucocorticoids (GC) represent the mainstay of treatment of idiopathic nephrotic syndrome (INS) and might be involved in the pathogenesis of the disease. We evaluated basal secretion of cortisol, number and affinity of glucocorticoid receptors, dexamethasone (Dex)-mediated inhibition of concanavalin-A (Con-A)-stimulated peripheral blood mononuclear cell (PBMC) proliferation, and cytokine secretion in patients with INS. Blood and saliva were obtained from 20 INS patients in relapse and 11 control patients. Cortisol concentrations were measured by radioimmunoassay. PBMC were isolated for binding and in vitro GC sensitivity assays. Cytokines were measured in supernatants of PBMC culture by enzyme-linked immunosorbent assay (ELISA). Salivary cortisol concentrations were similar in INS patients and control patients. Density and affinity of GC receptors were similar in steroid-sensitive (SS) patients and control, whereas in steroid-resistant (SR) patients they were variable. Lymphocyte proliferation after Con-A stimulation was inhibited by Dex in a dose-dependent manner in control and SS patients. Control and all clinically SS patients were steroid-sensitive by in vitro test, but control patients significantly presented more suppression of PBMC proliferation compared with SS patients. Basal- and Con-A-stimulated interleukin (IL)-6, IL-10, interferon (IFN)-gamma, and tumor necrosis factor (TNF)-alpha levels were similar in control and INS patients, and all cytokines but IL-10 were significantly inhibited by Dex 10-6 mol/L. In SR patients, cytokine secretion remained elevated after treatment with high doses of Dex. Abnormalities of number and affinity of the GC receptor and altered secretion of cytokines may be involved in tissue sensitivity to GC in INS patients.

The effects of dexmedetomidine and halothane on Fos expression in the spinal dorsal horn using a rat postoperative pain model

We investigated the effect of an intrathecal injection of a selective α2 adrenergic receptor agonist, dexmedetomidine (Dex), and halothane anesthesia on Fos expression in the lumbar spinal dorsal horn after skin incision of the planter surface of the hind paw, a postoperative pain model using rats. Fos immunoreactivity was induced particularly in the superficial layers of the spinal cord 2 h after surgery. Halothane anesthesia (0.5–1.5%) partially reversed Fos induction, but not in a dose-dependent manner. Preoperative spinal Dex (0.1–10 μg) dose-dependently reduced Fos immunoreactivity, while a relatively high dose of Dex (10 μg) was necessary to produce a profound effect. When used with halothane anesthesia, relatively low doses of Dex (1–3 μg) completely suppressed Fos induction in the superficial spinal layers. These findings indicate that preoperative Dex treatment may provide anesthesia that does not induce stress on spinal neurons.

Effects of dexamethasone on proliferation of and fibronectin synthesis by human primary prostatic stromal cells in vitro.

Glucocorticoids are anti inflammatory stress hormones and have been suggested to be involved in a large number of pathological processes. To test the effects of glucocorticoids on stromal prostatic cell growth and proliferation in vitro, the influence of a synthetic glucocorticoid (dexamethasone, dex) on recently established human primary cells from prostatic stroma (hPCPs) was analysed. The localization and distribution of the glucocorticoid receptor (GR) was investigated by immunohistochemistry. In addition, expression of the active isoform of the receptor (alpha-GR) was examined by reverse transcription PCR, and the effect of different doses of dex on proliferation of the stromal cells evaluated using 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) and amido black assays. alpha-GR mRNA was expressed by the hPCPs, and the GR protein was detected in the cytoplasm and nucleus of these cells. Incubating the cells with dex resulted in an enhanced cell proliferation that was mainly restricted to the fibroblasts. Moreover, fibronectin (FN) gene expression and secretion of the protein was increased by high doses of dex (> or = 10(-8) M), whereas low doses of dex (10(-10)M) showed no effect. Human prostatic stromal cells show sensitivity to dex in vitro, resulting in an increase in cell proliferation and FN synthesis. The authors assume that locally accumulating glucocorticoids can also influence the regulation of cell growth and extracellular matrix synthesis in the human prostate in vivo and may play a role in the pathologically altered prostate.

High dose of dexamethasone upregulates TCR/CD3-induced calcium response independent of TCR zeta chain expression in human T lymphocytes.

Glucocorticoids are very potent anti-inflammatory and immunosuppressive agents that modulate cellular immune responses, although, the molecular mechanisms that impart their complex effects have not been completely defined. We have previously demonstrated that dexamethasone (Dex), a synthetic glucocorticoid, biphasically modulates the expression of TCR (T cell receptor) zeta chain in human T cells. At 10 nM, it induced the expression of TCR zeta chain whereas at 100 nM, it inhibited its expression. In parallel to the upregulation of TCR zeta chain, the TCR/CD3-mediated [Ca(2+)](i) response was enhanced in 10 nM Dex-treated cells. However, at 100 nM, Dex treatment enhanced TCR/CD3-mediated [Ca(2+)](i) response without the induction of TCR zeta chain expression. Because the classical transcriptional model of glucocorticoid action cannot account for the effects of high dose of Dex, here we studied alternative mechanisms of action. We show that, increased and more sustained TCR/CD3-mediated [Ca(2+)](i) response was also observed in 100 nM Dex-treated cells in the presence of actinomycin D or cycloheximide suggesting that cellular transcription and/or de novo protein synthesis are not required for the induction. The TCR/CD3-mediated hyper [Ca(2+)](i) response in 100 nM Dex-treated cells was readily reversible by short-term culture in steroid-free medium. RU-486, a competitive antagonist of Dex, inhibited the increase in [Ca(2+)](i) response suggesting that the effect of Dex is mediated through the glucocorticoid receptor. Although the lipid-raft association of the TCR zeta chain was not significantly increased, high-dose of Dex increased the amount of ubiquitinated form of the TCR zeta chain in the cell membrane along with increased levels of actin. Fluorescence microscopy showed that high-dose of Dex alters the distribution of the TCR zeta chain and form more distinct clusters upon TCR/CD3 stimulation. These results suggest that high dose of Dex perturbs the membrane distribution of TCR zeta chain leading to more functional signaling clusters that result in increased TCR/CD3-mediated [Ca(2+)](i) response independent of TCR zeta chain expression.

A very high dose dexamethasone suppression test for differential diagnosis of Cushing's syndrome.

The high-dose dexamethasone (dex) suppression test of cortisol secretion (8 x 2 mg dex over two days or 8 mg overnight) is a mainstay in the differential diagnosis of Cushing's syndrome (CS). In some patients with pituitary Cushing's disease (CD), however, plasma cortisol is not suppressed to < 50% of control by 8 mg of dex. We therefore hypothesized that a higher dose of dex might produce more effective suppression of cortisol secretion in CD. We routinely tested the diagnostic efficacy of a very high dose of dex (32 mg, i.e. 4 x 8 mg in 24 hours) in comparison with the 8 mg overnight dex test in a population of patients with CD, in which an unusually high percentage was refractory to 8 mg dex. End points were the suppression of plasma cortisol, plasma ACTH and urinary free cortisol (UFC) to < 50% of control. Corticotrophin releasing hormone (human CRH) tests were also performed. Eleven out of 26 (11/26) patients with CD (42%), among them six with pituitary macro-adenomas, failed to show suppression of plasma cortisol after 8 mg dex. Five out of 19 patients (26%) with CD failed to suppress after 32 mg dex. Only 3/19 (16%) failed to suppress UFC after 32 mg dex. In nonpituitary CS (n = 11), only one patient with macro-nodular adrenal hyperplasia showed significant suppression of plasma cortisol, but not UFC, after 32 mg dex. ACTH suppression after 8 or 32 mg dex was often less pronounced than that of cortisol and was of no diagnostic value. Cortisol stimulation by > or = 23% after hCRH injection differentiated 100% of patients with CD from other forms of CS. In this series, the hCRH test was the most reliable test for the differential diagnosis of Cushing's syndrome. The 32 mg dexamethasone test with measurement of urinary free cortisol was clearly superior to the 8 mg test and to other aspects of the very high dose dexamethasone test. It can be recommended for 'non-suppressible' patients with ACTH-dependent Cushing's syndrome and can be performed on outpatients.

Treatment of Rats with Dexamethasone or Thyroxine Reverses Zinc Deficiency-Induced Intestinal Damage ,

Structural and functional damage to the intestine and the potential beneficial effects of dexamethasone (Dex) and thyroxine (T4) were examined in zinc-deficient rats. Rats were assigned to zinc deficient (ZD), control (C) or pair-fed (PF ) groups and fed for 40 d a zinc deficient (1 mg/kg) diet (ZD rats) or a similar diet supplemented with 50 mg Zn/kg (C and PF rats). Some rats of the ZD group were treated for the last 10 d with low (250 mg/kg) or high (5 mg/kg) doses of Dex or with T4 (100 mg/kg). Serum corticosterone of T4-treated ZD rats did not differ from untreated ZD rats. Serum T4 of T4-treated ZD rats did not differ from C rats. ZD rats developed ulcerations, inflammation and edema in the small intestine, particularly in the jejunum. PF rats did not show mucosal changes relative to C rats. ZD rats showed significantly lower crypt cell production rate (CCPR) and labeling index (LI) in the three intestinal regions, and lower cell migration rate and higher turnover time in the duodenum relative to C rats. Sucrase and maltase activities of ZD rats were significantly lower than C rats in the three mucosal regions. Treatment with the low dose of Dex resulted in fewer ulcerations compared with ZD rats. In rats administered the high dose of Dex or T4, all morphological alterations disappeared; the CCPR, LI, cell migration rate, cell turnover time and disaccharidase activities did not differ from C rats. In conclusion, Dex and T4 exert beneficial effects on zinc deficiency-induced intestinal alterations in rats.