Evidence of Reduced CBG Cleavage in Abdominal Obesity: A Potential Factor in Development of the Metabolic Syndrome.

Corticosteroid-binding globulin (CBG) is involved in the regulation of cortisol delivery. Neutrophil elastase-mediated cleavage of high to low affinity CBG (haCBG to laCBG) induces cortisol release at inflammatory sites. Past studies have shown reduced CBG in obesity, an inflammatory state, particularly in central adiposity/metabolic syndrome. We performed an observational, cross-sectional study of the effects of obesity, age and sex on ha/laCBG in 100 healthy volunteers. Total and haCBG levels were 11% higher in women but did not vary with age or menopausal status. Total CBG levels were lower with increased body weight and waist circumference; laCBG levels were lower with increased body weight, waist circumference, body mass index and body fat; higher haCBG levels were seen with increased body fat. The relation between CBG and adiposity appeared to be driven predominantly by the metabolic syndrome group. The results suggest reduced CBG cleavage in central obesity, possibly contributing to the characteristic inflammatory phenotype of the central obesity and metabolic syndrome. The mechanism of gender differences in CBG levels is unclear.

Corticosteroid-Binding Globulin: A Review of Basic and Clinical Advances.

Corticosteroid-binding globulin (CBG, transcortin) is the primary cortisol binding protein. It is a non-inhibitory serine protease inhibitor, capable of conformational change from a high cortisol-binding affinity form to a low affinity form upon cleavage of its reactive centre loop by various proteases, such as neutrophil elastase. The burgeoning inflammatory role of CBG applies to acute, severe inflammation where depletion is associated with mortality, and to chronic inflammation where defects in cortisol delivery may perpetuate inflammation. Naturally occurring human mutations influence a wide range of CBG properties and point toward a role in hitherto unexplained chronic musculoskeletal pain and fatigue disorders as well as potentially affecting fertility outcomes including offspring gender. In vitro and knock-out animal models of CBG propose a role for CBG in cortisol transport to the brain, providing a foundation for understanding the human observations in those with CBG mutations and sex differences in stress-related mood and behaviour. Finally, CBG measurement has a practical role in the estimation of free cortisol, useful in clinical circumstances where CBG levels or cortisol binding affinity is reduced. Taken together, novel data suggest a role for cortisol in targeted cortisol delivery, with implications in acute and chronic inflammation, as well as roles in metabolism and neurocognitive function, implying that CBG is a multifaceted component in the mechanisms of hypothalamic-pituitary-adrenal axis related homeostasis.

Depletion of high-affinity corticosteroid-binding globulin corresponds to illness severity in sepsis and septic shock; clinical implications.

OBJECTIVE: Corticosteroid-binding globulin (CBG) is cleaved by neutrophil elastase converting the high-affinity (haCBG) conformation of CBG to a low-affinity (laCBG) conformation with a ninefold reduced cortisol-binding affinity. These in vitro data suggest that cortisol release by CBG cleavage results in the targeted delivery of cortisol to areas of inflammation. Our objective was to determine whether CBG cleavage alters circulating levels of haCBG and laCBG in vivo in proportion to sepsis severity. DESIGN: Prospective, observational cohort study in an adult tertiary level Intensive Care Unit in Adelaide, Australia. PATIENTS: Thirty-three patients with sepsis or septic shock grouped by illness severity [sepsis, septic shock survivors, septic shock nonsurvivors and other shock]. MEASUREMENTS: Plasma levels of haCBG and laCBG were assessed using a recently developed in-house assay in patients. Plasma total and free cortisol levels were also measured. RESULTS: Plasma total CBG and haCBG levels fell significantly, in proportion to disease severity (P < 0·0001 for both). There was a nonsignificant increase in free and total cortisol as illness severity worsened (P = 0·19 and P = 0·39, respectively). Illness severity was better correlated with haCBG levels than either free or total cortisol levels. CONCLUSIONS: Increasing illness severity in sepsis and septic shock is associated with markedly reduced circulating haCBG concentrations in vivo. We propose that low levels of haCBG in chronic inflammation may limit the availability of cortisol to inflammatory sites, perpetuating the inflammatory process.

Modern Hydrocortisone Replacement Regimens in Adrenal Insufficiency Patients and the Risk of Adrenal Crisis.

The aim of this study was to examine the incidence of adrenal crises (AC) and the prescription of short-acting glucocorticoids (GC) in different geographic areas. To do this we conducted a descriptive study of AC hospitalisations and prescriptions for two GCs (hydrocortisone (HC) and cortisone acetate (CA)), and fludrocortisone acetate (FA), in different geographic areas of Australia between 1999/2000 and 2011/2012, using government databases.There were 2,584 hospital admissions for AC in Australia between 1999/00 and 2011/12 and the corresponding admission rates increased significantly from 7.4 to 11.1/10(6)/year (p<0.001). AC admission rates increased in 5 out of 6 geographic areas. Prescription rates for the combined GCs (HC/CA) increased at an annual rate of between 0.2-2.0% in all areas. All areas had significant (p<0.01) increases in HC prescription rates (4.5% to 13.7% annually) and CA prescription rates decreased in 5 out of the 6 regions (3.5% annual decrease to a 0.5% annual increase). When the geographic areas were combined, there was a significant correlation between the AC admission rates and HC/CA prescription rates (r=0.30, p<0.01). Admissions for AC and GC prescriptions increased significantly in Australia after 1999 and these varied significantly by geographic area. These results suggest that modern recommendations for lower dose, short-acting GC replacement may be of concern and further investigation is warranted.

Adrenal Insufficiency in Australia: Is it Possible that the Use of Lower Dose, Short-Acting Glucocorticoids has Increased the Risk of Adrenal Crises?

Morbidity from adrenal insufficiency (AI) in Australia is poorly described. The objective of this study was to evaluate AI morbidity patterns in adults between 1999/2000 and 2011/2012 using national databases. A descriptive study of hospitalisations for AI and adrenal crises (AC) in adults and trends in prescriptions for 2 short-acting glucocorticoids (GC) was designed. The setting was the Australian healthcare system. Main outcome measures are the trends in hospitalisation and prescription rates. There were 7,378 hospital admissions for treatment of AI in adults between 1999/00 and 2011/12. Of these, 29.5% were for an AC. Admission rates for AC increased from 9.5 to 12.4 admissions/10(6)/year (p < 0.05). There was a 5.8% decrease in admission rates for AI (excluding AC), from 27.0 to 25.5/10(6)/year (p = ns). Short-acting GC [hydrocortisone (HCT) and cortisone acetate (CA)] prescription rates increased significantly (p < 0.001) from 3,176.1/10(6) to 3,463.8/10(6). Prescription rates for CA decreased by 22.4% (p < 0.001) but HCT prescription rates increased to 77.1% (p < 0.001). The increase in AC admission rates was positively correlated with the rise in both the total GC prescription rate (r = 0.63, p < 0.05) and the HCT prescription rate (r = 0.74, p< 0.01). Over the 13-year study period, there was a 30.8% increase in hospitalisation rates for ACs and a concomitant 77.1% increase in prescribing of HCT. The association between AC events and HCT use and/or reduced effective GC dose is plausibly causal, but confirmatory studies are required before suggesting any change to GC replacement in AI.

Islet cell transplantation in Australia: screening, remote transplantation, and incretin hormone secretion in insulin independent patients.

Islet cell transplantation has emerged as a treatment modality for type 1 diabetes in the last 15 years due to the Edmonton protocol leading to consistent and sustained exogenous insulin independence post-transplantation. In recent years, consortia that involve both local and remote islet cell centers have been established, with local centers responsible for processing and shipping of islet cells, and remote centers only transplanting them. There are, however, few data on patient outcomes at remote centers. A tendency for high fasting glucose despite insulin independence was noted by us and others with an unknown mechanism. This review provides a brief history of islet cell transplantation, and focuses on the South Australian remote center experience: the challenges, screening criteria, and the impact on incretin hormone secretion of insulin independent transplant patients.

Multicenter Australian trial of islet transplantation: improving accessibility and outcomes.

Whilst initial rates of insulin independence following islet transplantation are encouraging, long-term function using the Edmonton Protocol remains a concern. The aim of this single-arm, multicenter study was to evaluate an immunosuppressive protocol of initial antithymocyte globulin (ATG), tacrolimus and mycophenolate mofetil (MMF) followed by switching to sirolimus and MMF. Islets were cultured for 24 h prior to transplantation. The primary end-point was an HbA1c of <7% and cessation of severe hypoglycemia. Seventeen recipients were followed for ≥ 12 months. Nine islet preparations were transported interstate for transplantation. Similar outcomes were achieved at all three centers. Fourteen of the 17 (82%) recipients achieved the primary end-point. Nine (53%) recipients achieved insulin independence for a median of 26 months (range 7-39 months) and 6 (35%) remain insulin independent. All recipients were C-peptide positive for at least 3 months. All subjects with unstimulated C-peptide >0.2 nmol/L had cessation of severe hypoglycemia. Nine of the 17 recipients tolerated switching from tacrolimus to sirolimus with similar graft outcomes. There was a small but significant reduction in renal function in the first 12 months. The combination of islet culture, ATG, tacrolimus and MMF is a viable alternative for islet transplantation.

The Emerging Role of Copeptin.

Direct measurement of the nonapeptide vasopressin has been limited by analyte instability ex vivo and in vivo rapid degradation, low serum concentrations requiring a sensitive assay and inherent secretory pulsatility. Copeptin is a 39 amino acid glycopeptide cleavage product of vasopressin synthesis with high stability, providing a marker of vasopressin secretion. Copeptin measurement has applications in diagnosis of diabetes insipidus and other diseases with altered vasopressin secretion. This review summarises our current understanding of serum copeptin measurement in diabetes insipidus and possible future applications of copeptin assays. As vasopressin is a stress hormone, there is emerging evidence on the use of copeptin for diagnosis and prognostication of disorders such as syndrome of inappropriate anti-diuretic hormone secretion, diabetes mellitus, critical illness, stroke, cardiovascular disease, respiratory disease, renal disease and thermal stress. Copeptin concentration measurement is likely to improve the diagnostic reliability of diabetes insipidus and, as a marker of stress, may have diagnostic or prognostic utility in specific clinical circumstances. Further studies are needed to determine if goal-directed therapy using plasma copeptin concentrations may improve patient outcomes.

Characteristics of plasma NOx levels in severe sepsis: high interindividual variability and correlation with illness severity, but lack of correlation with cortisol levels.

Objectives Nitric oxide (NO) concentrations are elevated in sepsis and their vasodilatory action may contribute to the development of hyperdynamic circulatory failure. Hydrocortisone infusion has been reported to reduce nitric oxide metabolite (NOx) concentrations and facilitate vasopressor withdrawal in septic shock. Our aim was to determine whether NOx concentrations relate to (i) protocol-driven vasopressor initiation and withdrawal and (ii) plasma cortisol concentrations, from endogenous and exogenous sources. Demonstration of a relation between NOx, cortisol and vasopressor requirement may provide an impetus towards the study of hydrocortisone-mediated NOx suppression as a tool in sepsis management. Design A prospective study of 62 patients with severe sepsis admitted to the intensive care unit. Measurements Plasma NOx, total and free cortisol, and corticosteroid-binding globulin (CBG) concentrations were measured and related to protocol-driven vasopressor use for 7 days following admission. Results Patients who developed septic shock (n = 35) had higher plasma NOx, total and free cortisol, and lower CBG concentrations than the nonseptic shock group (n = 27). Cortisol, CBG and NOx concentrations correlated with illness severity. Free cortisol, and to a lesser extent total cortisol, but not NOx concentrations, predicted septic shock. NOx concentrations were higher in nonsurvivors, and the concentrations were characteristically stable within individuals but marked interindividual differences were only partly accounted for by illness severity or renal dysfunction. NOx concentrations did not correlate with cortisol, did not relate to vasopressor requirement and did not fall after standard dose hydrocortisone, given for clinical indications. Conclusions Nitric oxide production increased with sepsis severity but did not correlate with plasma cortisol or vasopressor requirement. NOx levels were not suppressed reproducibly by hydrocortisone. High interindividual variability of NOx levels suggests that absolute NOx levels may not be a suitable target for individualized hydrocortisone therapy.

Screening for subclinical Cushing's syndrome in type 2 diabetes mellitus: low false-positive rates with nocturnal salivary cortisol.

The diagnosis of subclinical Cushing's syndrome (SCS) is important, but its relative rarity amongst patients with common metabolic disorders requires a simple test with a low false-positive rate. Using nocturnal salivary cortisol (NSC), which we first validated in patients with suspected and proven Cushing's syndrome, we screened 106 overweight patients with type 2 diabetes mellitus, a group at high risk of SCS and nontumoral hypothalamic-pituitary-adrenal axis perturbations. Our hypothesis was that a lower false-positive rate with NSC was likely, compared with that reported with the dexamethasone suppression test (DST) (10-20%), currently the foundation of diagnosis of SCS. No participant had clinically apparent Cushing's syndrome. Three participants had an elevated NSC but further testing excluded SCS. In this study, NSC had a lower false-positive rate (3%) than previously reported for the DST. Given the reported excellent performance of NSC in detection of hypercortisolism, the low false-positive rate in SCS suggests NSC may be superior to the DST for SCS screening. The NSC and DST should be compared directly in metabolic disorder patients; although our data suggest the patient group will need to be substantially larger to definitively determine the optimal screening test.

Systematic review: adrenal insufficiency secondary to swallowed topical corticosteroids in eosinophilic oesophagitis.

BACKGROUND: Swallowed topical corticosteroids are prescribed for eosinophilic oesophagitis (EoE), but there is a theoretical risk of adrenal insufficiency from their use. AIMS: To determine if the use of topical corticosteroids to treat EoE is associated with the development of adrenal insufficiency. METHOD: We conducted a systematic review of the published literature from January 1, 1950 to April 1, 2017 using Pubmed, Embase, Web of Science and Cochrane Central. Studies and meeting abstracts were included that described patients with EoE who received swallowed topical corticosteroids and any investigation for adrenal insufficiency. RESULTS: The search revealed 1610 unique publications, and 17 met inclusion criteria. There were 7 randomised controlled trials (RCTs), 6 prospective observational studies, 3 retrospective observational studies, and 1 case report. Cortisol measurements were performed on 596 individuals with EoE who received topical corticosteroids. Adrenal testing was abnormal, as defined by each study, in 94/596 patients (crude rate of 15.8%). Only 2 studies were considered to have a low risk of bias, being randomised controlled trials that estimated adrenal insufficiency in the active treatment and placebo groups, before and after treatment. None of the seven randomised controlled trials demonstrated statistically significantly different rates of adrenal insufficiency between topical corticosteroid and placebo over treatment intervals of 2-12 weeks. CONCLUSION: Topical corticosteroids were associated with adrenal insufficiency in a minority of patients. Most cases came from uncontrolled observational studies, with widely varying definitions of adrenal insufficiency. Longer follow-up and larger controlled studies are needed to quantify the risk of adrenal insufficiency with maintenance topical corticosteroid therapy in EoE.

Septic shock and sepsis: a comparison of total and free plasma cortisol levels.

CONTEXT: Severe systemic infection leads to hypercortisolism. Reduced cortisol binding proteins may accentuate the free cortisol elevations seen in systemic infection. Recently, low total cortisol increments after tetracosactrin have been associated with increased mortality and hemodynamic responsiveness to exogenous hydrocortisone in septic shock (SS), a phenomenon termed by some investigators as relative adrenal insufficiency (RAI). HYPOTHESIS: Free plasma cortisol may correspond more closely to illness severity than total cortisol, comparing SS and sepsis (S). DESIGN: This was a prospective study. SETTING: This study took place in a tertiary teaching hospital. PATIENTS: Patients had SS (n = 45) or S (n = 19) or were healthy controls (HCs; n = 10). AIM: The aim of the study was to compare total with free cortisol, measured directly and estimated by Coolens' method, corticosteroid-binding globulin (CBG), and albumin in patients with SS (with and without RAI) and S during acute illness, recovery, and convalescence. RESULTS: Comparing SS, S, and HC subjects, free cortisol levels reflected illness severity more closely than total cortisol (basal free cortisol, SS, 186 vs. S, 29 vs. HC, 13 nmol/liter, P < 0.001 compared with basal total cortisol, SS, 880 vs. S, 417 vs. HC, 352 nmol/liter, P < 0.001). Stimulated free cortisol increments varied greatly with illness category (SS, 192 vs. S, 115 vs. HC, 59 nmol/liter, P = 0.004), whereas total cortisol increments did not (SS, 474 vs. S, 576 vs. HC, 524 nmol/liter, P = 0.013). The lack of increase in total cortisol with illness severity is due to lower CBG and albumin. One third of patients with SS (15 of 45) but no S patients met a recently described criterion for RAI (total cortisol increment after tetracosactrin < or = 248 nmol/liter). RAI patients had higher basal total cortisol (1157 vs. 756 nmol/liter; P = 0.028) and basal free cortisol (287 vs. 140 nmol/liter; P = 0.017) than non-RAI patients. Mean cortisol increments in RAI were lower (total, 99 vs. 648 nmol/liter, P < 0.001; free, 59 vs. 252 nmol/liter, P < 0.001). These differences were not due to altered CBG or albumin levels. Free cortisol levels normalized more promptly than total cortisol in convalescence. Calculated free cortisol by Coolens' method compared closely with measured free cortisol. CONCLUSIONS: Free cortisol is likely to be a better guide to cortisolemia in systemic infection because it corresponds more closely to illness severity. The attenuated cortisol increment after tetracosactrin in RAI is not due to low cortisol-binding proteins. Free cortisol levels can be determined reliably using total cortisol and CBG levels.

A novel genetic locus for low renin hypertension: familial hyperaldosteronism type II maps to chromosome 7 (7p22).

Familial hyperaldosteronism type II (FH-II) is caused by adrenocortical hyperplasia or aldosteronoma or both and is frequently transmitted in an autosomal dominant fashion. Unlike FH type I (FH-I), which results from fusion of the CYP11B1 and CYP11B2 genes, hyperaldosteronism in FH-II is not glucocorticoid remediable. A large family with FH-II was used for a genome wide search and its members were evaluated by measuring the aldosterone:renin ratio. In those with an increased ratio, FH-II was confirmed by fludrocortisone suppression testing. After excluding most of the genome, genetic linkage was identified with a maximum two point lod score of 3.26 at theta=0, between FH-II in this family and the polymorphic markers D7S511, D7S517, and GATA24F03 on chromosome 7, a region that corresponds to cytogenetic band 7p22. This is the first identified locus for FH-II; its molecular elucidation may provide further insight into the aetiology of primary aldosteronism.

In vivo and in vitro characterization of antalarmin, a nonpeptide corticotropin-releasing hormone (CRH) receptor antagonist: suppression of pituitary ACTH release and peripheral inflammation.

Corticotropin-releasing hormone (CRH) secreted from the hypothalamus is the major regulator of pituitary ACTH release and consequent glucocorticoid secretion. CRH secreted in the periphery also acts as a proinflammatory modulator. CRH receptors (CRH-R1, R2alpha, R2beta) exhibit a specific tissue distribution. Antalarmin, a novel pyrrolopyrimidine compound, displaced 12SI-oCRH binding in rat pituitary, frontal cortex and cerebellum, but not heart, consistent with antagonism at the CRHR1 receptor. In vivo antalarmnin (20 mg/kg body wt.) significantly inhibited CRH-stimulated ACTH release and carageenin-induced subcutaneous inflammation in rats. Antalarmin, or its analogs, hold therapeutic promise in disorders with putative CRH hypersecretion, such as melancholic depression and inflammatory disorders.

Chronic effects of a nonpeptide corticotropin-releasing hormone type I receptor antagonist on pituitary-adrenal function, body weight, and metabolic regulation.

CRH, the principal regulator of the hypothalamic-pituitary-adrenal axis and modulator of autonomic nervous system activity, also participates in the regulation of appetite and energy expenditure. Antalarmin, a pyrrolopyrimidine compound, antagonizes CRH type 1 receptor-mediated effects of CRH, including pituitary ACTH release, stress behaviors, and acute inflammation. We administered antalarmin chronically to evaluate its effects on hypothalamic-pituitary-adrenal axis function and metabolic status. Adult male rats were treated twice daily with 20 mg/kg of i.p. antalarmin or placebo over 11 days. The animals were weighed; plasma ACTH, corticosterone, leptin, and blood glucose levels were determined; and morphometric analyses were performed to determine adrenal size and structure, including sizing, histochemistry, immunohistochemistry, and electron microscopy. Leptin messenger RNA expression in peripheral fat was analyzed by Northern blot. Antalarmin decreased plasma ACTH (mean +/- SD, 2.62 +/- 0.063 pg/ml) and corticosterone concentrations (10.21 +/- 1.80 microg/dl) compared with those in vehicle-treated rats [respectively, 5.3 +/- 2.0 (P < 0.05) and 57.02 +/- 8.86 (P < 0.01)]. Antalarmin had no significant effect on body weight, plasma leptin, or blood glucose concentrations or fat cell leptin messenger RNA levels. The width of the adrenal cortex of animals treated with antalarmin was reduced by 31% compared with that in controls without atrophy of the gland. On the ultrastructural level, adrenocortical cells were in a hypofunctional state characterized by reduced vascularization, increased content of lipid droplets, and tubulovesicular mitochondria with fewer inner membranes. The apoptotic rate was increased in the outer zona fasciculata of animals treated with the antagonist (26.6 +/- 3.58%) compared with that in placebo-treated controls (6.8 +/- 0.91%). We conclude that chronic administration of antalarmin does not affect body weight, carbohydrate metabolism, or leptin expression, whereas it reduces adrenocortical function mildly, without anatomical, clinical, or biochemical evidence of causing adrenal atrophy. These results are promising for future uses of such an antagonist in the clinic.

Human CYP11B2 (aldosterone synthase) maps to chromosome 8q24.3.

Aldosterone synthase (AS) is encoded by the CYP11B2 gene, a candidate for familial hypertension. CYP11B2 was previously mapped to chromosome 8q but its precise localization is necessary for genetic studies of hypertension. The present study reports the genetic mapping of the human CYP11B2 gene by radiation hybrid (RH) analysis, the isolation of a bacterial artificial chromosome (BAC) containing this gene and its physical mapping by fluorescent in situ hybridization (FISH). The CYP11B2 locus is on the most distal segment of the long arm of chromosome 8, proximal to the microsatellite polymorphic marker D8S1704. This location, which was confirmed by FISH, is approximately 60cM telomeric to the currently listed human gene locus (chromosome 8q21-22) and corresponds to cytogenetic band 8q24.3. The BACs containing the gene and a high-resolution map of the CYP11B2 locus are useful for genetic studies of hypertension and other endocrine disorders.

Adrenocorticotropin hyperresponse to the corticotropin-releasing hormone-mediated stimulus of naloxone in patients with myotonic dystrophy.

We previously showed that CRH-mediated stimuli, including exogenous CRH, cause ACTH hypersecretion in many myotonic dystrophy (DM) patients. We confirmed this by giving naloxone, a stimulator of endogenous CRH release, to a large number of DM patients and controls. DM patients, first degree relatives, and normal controls received i.v. naloxone at 1400 h, and blood was taken for ACTH (RIA) and cortisol (high pressure liquid chromatography) measurements from 15 min before to 120 min after naloxone treatment. DM patients had basal ACTH levels approximately twice those of controls, and their ACTH responses were 4 times those of controls. In contrast, DM basal cortisol levels were not significantly different from those of relatives and were slightly higher than those of normal subjects. Cortisol responses were similar in the three groups, probably due to attenuation at high levels of adrenocortical stimulation, although some patients with inappropriately low cortisol responses for their level of ACTH stimulation warrant further investigation. Nineteen of the 36 patients whose ACTH responses were greater than 3 SD above the normal mean were classed as hyperresponders. Seven patients, who were tested more than once, had reproducible responses relative to those of the normal subjects. We conclude that ACTH hypersecretion after CRH-mediated stimuli, including naloxone, is an inherent, but variable, feature of DM, caused by expression of the genetic mutation at the anterior pituitary. The mechanism is probably a defect in the intracellular pathway initiated by CRH-receptor interaction as a result of abnormal levels of a cAMP-dependent kinase, DMPK, the product of the gene undergoing mutation in DM.

The effect of desipramine on basal and naloxone-stimulated cortisol secretion in humans: interaction of two drugs acting on noradrenergic control of adrenocorticotropin secretion.

Desipramine (DMI), a tricyclic antidepressant and norepinephrine (NE) reuptake blocker, is reported to induce ACTH and cortisol release acutely in humans, probably by facilitating central NE neurotransmission. Tricyclic antidepressant therapy, including DMI, normalizes the ACTH and cortisol hypersecretion that often accompanies depression. The mechanism of hypothalamic-pituitary-adrenal (HPA) axis inhibition by DMI in humans is unknown. In rats, DMI reduces the activity of the locus ceruleus, a major source of NE innervation of the hypothalamic paraventricular nucleus, the site of CRH neurons. Naloxone induces ACTH and cortisol release in humans through a noradrenergic-mediated mechanism and a probable consequent stimulation of hypothalamic CRH release. To study the interaction of these drugs on NE neurotransmission and, hence, HPA axis activity in humans, we administered DMI alone and with naloxone in a randomized, double blind, placebo-controlled protocol in eight healthy male volunteers. DMI (75 mg, orally) was given 180 min before naloxone (125 micrograms/kg BW, i.v.). Plasma ACTH and cortisol were measured at frequent intervals from 60 min before to 120 min after naloxone treatment. Plasma cortisol levels were 77% higher 180 min after DMI compared to those after placebo treatment (287 +/- 17 vs. 162 +/- 14 nmol/L; P = 0.000005). DMI reduced the naloxone-induced rise in cortisol (P = 0.02), but there was no change in the integrated cortisol response. The increase in basal plasma ACTH levels after DMI treatment did not reach statistical significance. DMI significantly increased systolic blood pressure and heart rate consistent with an effect on the noradrenergic control of the cardiovascular system. In summary, DMI increased basal cortisol levels consistent with facilitation of NE neurotransmission and, hence, hypothalamic CRH release. However, DMI had no enhancing effect on naloxone-induced cortisol release. This contrasts with the synergy observed when non-antidepressant agents that increase NE neurotransmission are given with naloxone to humans. DMI increases glucocorticoid feedback sensitivity in the rat HPA axis after several weeks through up-regulation of central corticosteroid receptors. However, this slowly developing effect is unlikely to occur during these acute studies. The effect of DMI on naloxone-induced cortisol release is consistent with an inhibitory effect on central noradrenergic control of ACTH release, perhaps at the locus ceruleus. This is the first human study to suggest an inhibitory effect of DMI on central noradrenergic control of ACTH release.