Diabetes impairs hypothalamo-pituitary-adrenal (HPA) responses to hypoglycemia, and insulin treatment normalizes HPA but not epinephrine responses

Captopril inhibits the overproduction of proopiomelanocortin and adrenocorticotropic hormone in the pituitary gland of male diabetic mice in close relationship with an increase in glucocorticoid receptor expression

Prior investigation shows that diabetic patients present hypothalamus-pituitary-adrenal (HPA) axis hyperactivity related to impaired negative feedback. This study investigates the effect of Captopril on the overproduction of adrenocorticotropic hormone (ACTH) and its precursor proopiomelanocortin (POMC) in the pituitary gland of male diabetic mice. Diabetes was induced by intravenous injection of alloxan into fasted Swiss-webster mice, and the animals were treated with Captopril for 14 consecutive days, starting 7 days post-diabetes induction. Plasma corticosterone levels were evaluated by ELISA, while pituitary gland expressions of angiotensin-II type 1 receptor (AT1), angiotensin-II type 2 receptor (AT2), ACTH, Bax, Bcl-2, KI-67, POMC, and glucocorticoid receptor (GR) were evaluated using immunohistochemistry or Western blot. Diabetic mice showed pituitary gland overexpression of AT1, without altering AT2 levels, which were sensitive to Captopril treatment. Furthermore, diabetic mice presented hypercortisolism, along with an increase in the number of corticotroph cells, POMC and ACTH expression, and number of proliferative cells, and a decrease of GR expression in the pituitary gland. In addition, treatment with Captopril reduced systemic corticosterone levels, corticotroph and proliferative cell numbers, and Bcl-2, POMC, and ACTH expression in the pituitary gland of diabetic mice, besides increasing the expression of Bax and GR. In conclusion, these findings show that Captopril is a promising therapy for treating complications associated with HPA axis hyperactivity in diabetic patients, in a mechanism probably related to the downregulation of POMC production in the pituitary gland and subsequent reduction of systemic corticosterone levels.

Role of the Adrenal Medulla in Hypoglycaemia-Associated Autonomic Failure-A Diabetic Perspective

Hypoglycaemia-associated autonomic failure (HAAF) is characterised by an impairment in adrenal medullary and neurogenic symptom responses following episodes of recurrent hypoglycaemia. Here, we review the status quo of research related to the regulatory mechanisms of the adrenal medulla in its response to single and recurrent hypoglycaemia in both diabetic and non-diabetic subjects with particular focus given to catecholamine synthesis, enzymatic activity, and the impact of adrenal medullary peptides. Short-term post-transcriptional modifications, particularly phosphorylation at specific residues of tyrosine hydroxylase (TH), play a key role in the regulation of catecholamine synthesis. While the effects of recurrent hypoglycaemia on catecholamine synthetic enzymes remain inconsistent, long-term changes in TH protein expression suggest species-specific responses. Adrenomedullary peptides such as neuropeptide Y (NPY), galanin, and proenkephalin exhibit altered gene and protein expression in response to hypoglycaemia, suggesting a potential role in the modulation of catecholamine secretion. Of note is NPY, since its antagonism has been shown to prevent reductions in TH protein expression. This review highlights the need for further investigation into the molecular mechanisms involved in the adrenal medullary response to hypoglycaemia. Despite advancements in our understanding of HAAF in non-diabetic rodents, a reliable diabetic rodent model of HAAF remains a challenge.

Dysregulated Hypothalamic–Pituitary–Adrenal Axis Is Associated With Increased Inflammation and Worse Outcomes After Ischemic Stroke in Diabetic Mice

Diabetic patients have larger infarcts, worse neurological deficits, and higher mortality rate after an ischemic stroke. Evidence shows that in diabetes, the hypothalamic–pituitary–adrenal (HPA) axis was dysregulated and levels of cortisol increased. Based on the role of the HPA axis in immunity, we hypothesized that diabetes-dysregulated stress response exacerbates stroke outcomes via regulation of inflammation. To test this hypothesis, we assessed the regulation of the HPA axis in diabetic mice before and after stroke and determined its relevance in the regulation of post-stroke injury and inflammation. Diabetes was induced in C57BL/6 mice by feeding a high-fat diet and intraperitoneal injection of streptozotocin (STZ), and then the mice were subjected to 30 min of middle cerebral artery occlusion (MCAO). Infarct volume and neurological scores were measured in the ischemic mice. The inflammatory cytokine and chemokine levels were also determined in the ischemic brain. To assess the effect of diabetes on the stroke-modulated HPA axis, we measured the expression of components in the HPA axis including corticotropin-releasing hormone (CRH) in the hypothalamus, proopiomelanocortin (POMC) in the pituitary, and plasma adrenocorticotropic hormone (ACTH) and corticosterone. Diabetic mice had larger infarcts and worse neurological scores after stroke. The exacerbated stroke outcomes in diabetic mice were accompanied by the upregulated expression of inflammatory factors (including IL-1β, TNF-α, IL-6, CCR2, and MCP-1) in the ischemic brain. We also confirmed increased levels of hypothalamic CRH, pituitary POMC, and plasma corticosterone in diabetic mice before and after stroke, suggesting the hyper-activated HPA axis in diabetic conditions. Finally, we confirmed that post-stroke treatment of metyrapone (an inhibitor of glucocorticoid synthesis) reduced IL-6 expression and the infarct size in the ischemic brain of diabetic mice. These results elucidate the mechanisms in which the HPA axis in diabetes exacerbates ischemic stroke. Maintaining an optimal level of the stress response by regulating the HPA axis may be an effective approach to improving stroke outcomes in patients with diabetes.

ZT-01: A novel somatostatin receptor 2 antagonist for restoring the glucagon response to hypoglycaemia in type 1 diabetes

AIM

To evaluate the pharmacokinetics and efficacy of a novel somatostatin receptor 2 antagonist, ZT-01, to stimulate glucagon release in rats with type 1 diabetes (T1D).

METHODS

The pharmacokinetics of ZT-01 and PRL-2903 were assessed following intraperitoneal or subcutaneous dosing at 10 mg/kg. We compared the efficacy of ZT-01 with PRL-2903 to prevent hypoglycaemia during an insulin bolus challenge and under hypoglycaemic clamp conditions.

RESULTS

Within 1 hour after intraperitoneal administration, ZT-01 achieved more than 10-fold higher plasma Cmax compared with PRL-2903. Twenty-four hour exposure was 4.7× and 11.3× higher with ZT-01 by the intraperitoneal and subcutaneous routes, respectively. The median time to reach hypoglycaemia of more than 3.0 mmol/L was 60, 70, and 125 minutes following vehicle, PRL-2903, or ZT-01 administration, respectively. Furthermore, rats receiving ZT-01 had significantly higher glucose nadirs following insulin administration compared with PRL-2903- and vehicle-treated rats. During the hypoglycaemic clamp, ZT-01 increased peak glucagon responses by ~4-fold over PRL-2903.

CONCLUSIONS

We conclude that ZT-01 may be effective in restoring glucagon responses and preventing the onset of hypoglycaemia in patients with T1D.

Glucocorticoid Receptor Signaling in Diabetes

Stress and depression increase the risk of Type 2 Diabetes (T2D) development. Evidence demonstrates that the Glucocorticoid (GC) negative feedback is impaired (GC resistance) in T2D patients resulting in Hypothalamic-Pituitary-Adrenal (HPA) axis hyperactivity and hypercortisolism. High GCs, in turn, activate multiple aspects of glucose homeostasis in peripheral tissues leading to hyperglycemia. Elucidation of the underlying molecular mechanisms revealed that Glucocorticoid Receptor (GR) mediates the GC-induced dysregulation of glucose production, uptake and insulin signaling in GC-sensitive peripheral tissues, such as liver, skeletal muscle, adipose tissue, and pancreas. In contrast to increased GR peripheral sensitivity, an impaired GR signaling in Peripheral Blood Mononuclear Cells (PBMCs) of T2D patients, associated with hyperglycemia, hyperlipidemia, and increased inflammation, has been shown. Given that GR changes in immune cells parallel those in brain, the above data implicate that a reduced brain GR function may be the biological link among stress, HPA hyperactivity, hypercortisolism and hyperglycemia. GR polymorphisms have also been associated with metabolic disturbances in T2D while dysregulation of micro-RNAs—known to target GR mRNA—has been described. Collectively, GR has a crucial role in T2D, acting in a cell-type and context-specific manner, leading to either GC sensitivity or GC resistance. Selective modulation of GR signaling in T2D therapy warrants further investigation.

Brain-Body Control of Glucose Homeostasis-Insights From Model Organisms

Tight regulation of blood glucose is essential for long term health. Blood glucose levels are defended by the correct function of, and communication between, internal organs including the gastrointestinal tract, pancreas, liver, and brain. Critically, the brain is sensitive to acute changes in blood glucose level and can modulate peripheral processes to defend against these deviations. In this mini-review we highlight select key findings showcasing the utility, strengths, and limitations of model organisms to study brain-body interactions that sense and control blood glucose levels. First, we discuss the large platform of genetic tools available to investigators studying mice and how this field may yet reveal new modes of communication between peripheral organs and the brain. Second, we discuss how rats, by virtue of their size, have unique advantages for the study of CNS control of glucose homeostasis and note that they may more closely model some aspects of human (patho)physiology. Third, we discuss the nascent field of studying the CNS control of blood glucose in the zebrafish which permits ease of genetic modification, large-scale measurements of neural activity and live imaging in addition to high-throughput screening. Finally, we briefly discuss glucose homeostasis in drosophila, which have a distinct physiology and glucoregulatory systems to vertebrates.

Hypothalamic insulin signalling as a nexus regulating mood and metabolism

Insulin has long been known as a metabolic hormone critical in the treatment of diabetes for its peripheral effects on blood glucose. However, in the last 50 years, insulin has entered the realm of neuroendocrinology and many studies have described its function on insulin receptors in the brain in relation to both metabolic and mood disorders. Indeed, rodent models of impaired insulin signalling show signs of dysregulated energy and glucose homeostasis, as well as anxiety-like and depressive behaviours. Importantly, many metabolic diseases such as obesity and diabetes increase the risk of developing mood disorders; however, the brain mechanisms underlying the connection between metabolism and mood remain unresolved. We present the current literature on the importance of the insulin receptor with respect to regulating glucose and energy homeostasis and mood-related behaviours. Specifically, we hypothesise that the insulin receptor in the hypothalamus, classically known as the homeostatic centre of the brain, plays a causal role in linking metabolic and behavioural effects of insulin signalling. In this review, we discuss insulin signalling in the hypothalamus as a critical point of neural integration controlling metabolism and mood.

Experimental Models of Impaired Hypoglycaemia-Associated Counter-Regulation

Impaired awareness of hypoglycaemia (IAH) affects around a quarter of patients with diabetes who receive insulin treatment. This condition is characterised by a progressive reduction in symptomatic and behavioural responses to hypoglycaemia, increasing risk of deeper drops in blood glucose, unconsciousness, and collapse. Thus, patients with IAH experience severe hypoglycaemic episodes more frequently, resulting in significant morbidity and mortality. IAH is thought to develop as a consequence of whole-body adaptations to repeated insulin-induced hypoglycaemia (RH), with widespread deficits in the hypoglycaemia counter-regulatory response (CRR). Despite this important insight, the precise pathophysiology by which RH leads to an attenuated CRR is unknown. Studies into the underlying mechanisms of IAH have employed a variety of protocols in humans and experimental species. The use of animal models has many investigational benefits, including the unprecedented increase in the availability of transgenic strains. However, modelling impaired hypoglycaemia-associated counter-regulation remains challenging and appropriate interpretation of findings across species and protocols even more so. Here, we review the experimental modelling of IAH and impaired hypoglycaemia-associated counter-regulation, with a focus on understanding species-specific variation in glucose homeostasis. This review will aid investigators in interpreting outputs from different studies in IAH and aid progress in the field.

Sex-dependent effects of ambient PM2.5 pollution on insulin sensitivity and hepatic lipid metabolism in mice

Background & aims

Emerging evidence supports ambient fine particulate matter (PM_2.5) exposure is associated with insulin resistance (IR) and hepatic lipid accumulation. In this study, we aimed to evaluate the sex-dependent vulnerability in response to PM_2.5 exposure and investigate the underlying mechanism by which PM_2.5 modulates hepatic lipid metabolism.

Methods

Both male and female C57BL/6 mice were randomly assigned to ambient PM_2.5 or filtered air for 24 weeks via a whole body exposure system. High-coverage quantitative lipidomics approaches and liquid chromatography-mass spectrometry techniques were performed to measure hepatic metabolites and hormones in plasma. Metabolic studies, histological analyses, as well as gene expression levels and molecular signal transduction analysis were applied to examine the effects and mechanisms by which PM_2.5 exposure-induced metabolic disorder.

Results

Female mice were more susceptible than their male counterparts to ambient PM_2.5 exposure-induced IR and hepatic lipid accumulation. The hepatic lipid profile was changed in response to ambient PM_2.5 exposure. Levels of hepatic triacylglycerols (TAGs), free fatty acids (FFAs) and cholesterol were only increased in female mice from PM group compared to control group. Plasmalogens were dysregulated in the liver from PM_2.5-exposed mice as well. In addition, exposure to PM_2.5 led to enhanced hepatic ApoB and microsomal triglyceride transport protein expression in female mice. Finally, PM_2.5 exposure inhibited hypothalamus-pituitary-adrenal (HPA) axis and decreased glucocorticoids levels, which may contribute to the vulnerability in PM_2.5-induced metabolic dysfunction.

Conclusions

Ambient PM_2.5 exposure inhibited HPA axis and demonstrated sex-associated differences in its effects on IR and disorder of hepatic lipid metabolism. These findings provide new mechanistic evidence of hormone regulation in air pollution-mediated metabolic abnormalities of lipids and more personalized care should be considered in terms of sex-specific risk factors.

Insulin Resistance as a Shared Pathogenic Mechanism Between Depression and Type 2 Diabetes

Neuropsychiatric disorders and type 2 diabetes (T2D) are major public health concerns proposed to be intimately connected. T2D is associated with increased risk of dementia, neuropsychiatric and mood disorders. Evidences of the involvement of insulin signaling on brain mechanisms related to depression indicate that insulin resistance, a hallmark of type 2 diabetes, could develop in the brains of depressive patients. In this article, we briefly review possible molecular mechanisms associating defective brain insulin signaling with reward system, neurogenesis, synaptic plasticity and hypothalamic-pituitary-adrenal (HPA) stress axis in depression. We further discuss the involvement of tumor necrosis factor α (TNFα) promoting defective insulin signaling and depressive-like behavior in rodent models. Finally, due to the high resistant rate of anti-depressants, novel insights into the link between insulin resistance and depression may advance the development of alternative treatments for this disease.

Cerebrovascular dysfunction with stress and depression

Maintenance of adequate tissue perfusion through a dense network of cerebral microvessels is critical for the perseveration of normal brain function. Regulation of the cerebral blood flow has to ensure adequate delivery of nutrients and oxygen with moment-to-moment adjustments to avoid both hypo- and hyper-perfusion of the brain tissue. Even mild impairments of cerebral blood flow regulation can have significant implications on brain function. Evidence suggests that chronic stress and depression elicits multifaceted functional impairments to the cerebral microcirculation, which plays a critical role in brain health and the pathogenesis of stress-related cognitive impairment and cerebrovascular events. Identifying the functional and structural changes to the brain that are induced by stress is crucial for achieving a realistic understanding of how related illnesses, which are highly disabling and with a large economic cost, can be managed or reversed. This overview discusses the stress-induced alterations in neurovascular coupling with specific attention to cerebrovascular regulation (endothelial dependent and independent vasomotor function, microvessel density). The pathophysiological consequences of cerebral microvascular dysfunction with stress and depression are explored.

Diabetes mellitus prevalence in patients with takotsubo syndrome: the case of the brain-heart disconnect

BACKGROUND

Hyperactive autonomic nervous system (ANS) is among the postulated pathophysiologic mechanisms of takotsubo syndrome (TTS). Diabetes mellitus (DM) with its associated ANS peripheral neuropathy could exert a "protective" influence for the emergence of TTS.

METHODS

A patient-based meta-analysis of the data obtained from all patients presented individually was carried out, focusing on age, gender, and history of hypertension (HTN) and DM.

RESULTS

The prevalences of HTN and DM for all 2,342 patients, aged 61.1 ± 17.3, 85.1% female, were 37.4% and 9.5%, for patients ≥ 60 years old were 45.8% and 11.7%, and for patients ≥65 years old were 48.2% and 12.3%, correspondingly. The prevalence of DM in patients with TTS is less than half of the world's and USA's elderly populations.

CONCLUSIONS

Prevalence of DM in patients with TTS is lower than in the general population, suggesting that DM, may have a "protective" effect for the emergence of TTS.

Metabolomics reveals new metabolic perturbations in children with type 1 diabetes

OBJECTIVE

Using an untargeted metabolomics approach we investigated the metabolome of children with type 1 diabetes (T1D) in comparison with healthy peers and explored the contribution of HbA1c and clinical features to the observed difference.

RESEARCH DESIGN AND METHODS

We enrolled children with T1D aged 6-15 years, attending the pediatric diabetes clinic of University of Padova (Italy). Healthy controls were enrolled on voluntary basis and matched for age, sex, pubertal status, body mass index (BMI). We performed a liquid chromatography and mass spectrometry analysis (LC-MS) on fasting urinary samples of the 2 groups.

RESULTS

A total of 56 patients with T1D aged (11.4 ± 2.2) years, and 30 healthy controls (10.7 ± 2.8) years were enrolled. We identified 59 urinary metabolites having a higher level in children with T1D, mainly represented by gluco- and mineralcorticoids, phenylalanine and tryptophan catabolites (kynurenine), small peptides, glycerophospholipids, fatty acids, and gut bacterial products. We did not find any association between HbA1c, pubertal status, disease duration, and metabolome profile within the case group.

CONCLUSIONS

T1D profoundly disrupts the metabolome of pediatric patients. The excess of cortisol and aldosterone may contribute to the development of macrovascular complications in adulthood, while the increase of tryptophan derivates may have a role in neuronal damage associated to hyperglycemia. Determinants of such findings, other than HbA1c, should be explored.

Prediabetes in youth - mechanisms and biomarkers

Obesity has been estimated to decrease life expectancy by as little as 0.8 to as much as 7 years being the second leading cause of preventable death in the United States after smoking. Along with the increase in the prevalence of obesity, there has been a dramatic rise of the prevalence of prediabetes and type 2 diabetes among adolescents. Despite that, very little is known about the pathogenesis of these conditions in pediatrics and about how we could detect prediabetes in an early stage in order to prevent full blown diabetes. In this review we summarize the current knowledge on the pathophysiology of prediabetes and type 2 diabetes in adolescents and describe how biomarkers of beta-cell function might help identifying those individuals who are prone to progress from normal glucose tolerance towards prediabetes and overt type 2 diabetes. To better understand and fight this disease, we will need to explore and develop novel therapeutic strategies and individuate more sensitive and specific biomarkers that can allow an earlier detection of the disease.

Stressing diabetes? The hidden links between insulinotropic peptides and the HPA axis

Diabetes mellitus exerts metabolic stress on cells and it provokes a chronic increase in the long-term activity of the hypothalamus-pituitary-adrenocortical (HPA) axis, perhaps thereby contributing to insulin resistance. GLP-1 receptor (GLP-1R) agonists are pleiotropic hormones that not only affect glycaemic and metabolic control, but they also produce many other effects including activation of the HPA axis. In fact, several of the most relevant effects of GLP-1 might involve, at least in part, the modulation of the HPA axis. Thus, the anorectic activity of GLP-1 could be mediated by increasing CRF at the hypothalamic level, while its lipolytic effects could imply a local increase in glucocorticoids and glucocorticoid receptor (GC-R) expression in adipose tissue. Indeed, the potent activation of the HPA axis by GLP-1R agonists occurs within the range of therapeutic doses and with a short latency. Interestingly, the interactions of GLP-1 with the HPA axis may underlie most of the effects of GLP-1 on food intake control, glycaemic metabolism, adipose tissue biology and the responses to stress. Moreover, such activity has been observed in animal models (mice and rats), as well as in normal humans and in type I or type II diabetic patients. Accordingly, better understanding of how GLP-1R agonists modulate the activity of the HPA axis in diabetic subjects, especially obese individuals, will be crucial to design new and more efficient therapies for these patients.

Enhanced nitric oxide generation from nitric oxide synthases as the cause of increased peroxynitrite formation during acute restraint stress: Effects on carotid responsiveness to angiotensinergic stimuli in type-1 diabetic rats

Diabetes mellitus is associated with reactive oxygen and nitrogen species accumulation. Behavioral stress increases nitric oxide production, which may trigger a massive impact on vascular cells and accelerate cardiovascular complications under oxidative stress conditions such as Diabetes. For this study, type-1 Diabetes mellitus was induced in Wistar rats by intraperitoneal injection of streptozotocin. After 28 days, cumulative concentration-response curves for angiotensin II were obtained in endothelium-intact carotid rings from diabetic rats that underwent to acute restraint stress for 3h. The contractile response evoked by angiotensin II was increased in carotid arteries from diabetic rats. Acute restraint stress did not alter angiotensin II-induced contraction in carotid arteries from normoglycaemic rats. However acute stress combined with Diabetes increased angiotensin II-induced contraction in carotid rings. Western blot experiments and the inhibition of nitric oxide synthases in functional assays showed that neuronal, endothelial and inducible nitric oxide synthase isoforms contribute to the increased formation of peroxynitrite and contractile hyperreactivity to angiotensin II in carotid rings from stressed diabetic rats. In summary, these findings suggest that the increased superoxide anion generation in carotid arteries from diabetic rats associated to the increased local nitric oxide synthases expression and activity induced by acute restrain stress were responsible for exacerbating the local formation of peroxynitrite and the contraction induced by angiotensin II.

The Adrenal Gland Volume Measurements in Manifestation of the Metabolic Status in Type-2 Diabetes Mellitus Patients

Objectives. The aim of our study was to investigate the differences in adrenal gland volume between nondiabetic controls and Type-2 diabetic patients and to examine the influence of glycemic control in diabetes mellitus on adrenal gland volume. Methods. From March 2 to November 25, 2015, 62 consecutive patients with Type-2 DM along with 62 nondiabetics matched by age, gender, and BMI were enrolled in this prospective study. Our diabetes patients were categorized into two groups, well-controlled and poorly controlled diabetes groups. Adrenal volumetric measurements were performed by two radiologists, prospectively and independently, with semiautomatic software. Interobserver reliability was studied using the interobserver correlation coefficient (ICC). Results. The total adrenal volume (TAV) was significantly higher in Type-2 diabetic patients when compared with nondiabetic patients (p < 0.05). When we investigated diabetic patients according to glycemic controls, the TAVs in controlled diabetic patients were significantly higher than in those of the poorly controlled or uncontrolled diabetic patients (p < 0.05). Nondiabetic control patients have significantly smaller TAVs when compared to controlled and poorly or noncontrolled diabetic patients (p < 0.05). Conclusion. Our study suggests that adrenal gland volume measurement may be used as an indirect marker of glycemic control in patients with diabetes.

Low prevalence of diabetes mellitus in patients with Takotsubo syndrome: A plausible 'protective' effect with pathophysiologic connotations

AIMS

The pathophysiology of Takotsubo syndrome is still elusive; coronary vasospasm, microvascular dysfunction, or catecholamine-mediated injury to the cardiomyocytes, effected by local release from the autonomic nerves and/or blood-borne catecholamines, are considered as tentative cause(s). Diabetes mellitus-induced autonomic neuropathy leads to a brain-heart disconnection, and it can conceivably ameliorate/block the effect of an unbridled adrenergic storm to the heart, and the emergence of Takotsubo syndrome. This study sought to evaluate the prevalence of diabetes mellitus in patients with Takotsubo syndrome.

METHODS AND RESULTS

All the papers accessed in PubMed were reviewed, to evaluate the prevalence of diabetes mellitus and hypertension in Takotsubo syndrome patients, employing the rate of the latter as an index of how representative of the general population were the study patients, and the rate of the former as the focus of this investigation. Out of the 1932 papers, 959 were suitable for analysis, reporting on 33,894 patients (88.9% women) with Takotsubo syndrome. In five subanalyses, of all patients, patients reported individually, patients reported collectively in case series, patients ⩾ 60 years old reported individually, and patients ⩾ 65 years old reported individually, the prevalence of hypertension was 57.4%, 42.8%, 57.9%, 50.4%, and 52.2%, correspondingly, and comparable to the 65.4% shown by the National Health and Nutrition Examination Survey (NHANES). The prevalence of diabetes mellitus in the five subgroups was 16.8%, 10.2%, 17.0%, 11.9%, and 12.5%, correspondingly, and lower than the 26.9% found by the NHANES.

CONCLUSION

The prevalence of diabetes mellitus in patients with Takotsubo syndrome is low. This insight may be useful for the diagnosis, pathophysiology unraveling, and employment of autonomic adrenergic blocking agents in the management of patients with Takotsubo syndrome.

Corticotropic axis drive of overnight cortisol secretion is suppressed in adolescents and young adults with type 1 diabetes mellitus

CONTEXT

Type 1 diabetes mellitus (T1DM) is a pro-inflammatory stress state, which, with its attendant hyperglycemia, likely disrupts hypothalamo-pituitary-adrenal (HPA) control, further dysregulating glucose homeostasis.

OBJECTIVE

To test the hypothesis that endogenous adrenocorticotropic hormone (ACTH)-cortisol dose-responsive drive, estimated analytically, is significantly accentuated in adolescents and young adults with T1DM compared with healthy individuals.

DESIGN, SETTING, PATIENTS, AND INTERVENTIONS

This was a pilot study of 11 volunteers with T1DM and 10 controls, ages 16-30 yr, at a medical center. Subjects underwent overnight frequent blood sampling (every 10 min for ACTH and cortisol and every 60 min for blood glucose) from 10 pm to 8 am. T1DM volunteers maintained their home insulin regimen.

MAIN OUTCOMES

Deconvolution analysis and dose-response estimates were the key outcomes.

RESULTS

Mean free cortisol, but not ACTH, concentrations were lower in the T1DM group compared with controls (p = 0.012). Non-invasive ACTH-cortisol dose-response estimates revealed that T1DM patients had reduced ACTH efficacy (maximal cortisol secretion, p = 0.009), reduced ACTH potency as quantified by greater EC50 (ACTH concentration driving half-maximal cortisol secretion, p = 0.04), and increased ACTH sensitivity (more positive ACTH-cortisol slope, p = 0.03). Post-hoc gender comparisons indicated that these differences were limited to females. Linear regression in women showed a strong correlation of both ACTH efficacy and EC50 with C-peptide levels (both p < 0.01).

CONCLUSION

Compared with healthy individuals, T1DM patients manifest decreased overnight adrenal responsiveness to endogenous ACTH leading to lower free cortisol concentrations. These findings suggest impaired stress-related adaptations of the HPA axis in T1DM.

Cortisol hyporesponsiveness to the low dose ACTH test is a frequent finding in a pediatric population with type 1 diabetes mellitus

INTRODUCTION

In adults with type 1 diabetes mellitus (DM1), a 25% of risk of hypocortisolism has been found through a low dose ACTH test with negative antibodies suggesting other causes of hypothalamic-pituitary-adrenal axis dysfunction.

AIM

To evaluate adrenal function in pediatric patients with DM1 and correlate the results with the frequency of hypoglycemia and metabolic control.

METHODS

Sixty-nine patients were enrolled, age 12.3 (5.7-18.1); 50 boys and 19 girls. A 20% had additional autoimmune diseases. Mean hemoglobin A1c (HbA1c) was 8.1% and insulin dose was 1.14 U/kg/d. After an overnight fast, a low dose ACTH test (1 µg) was performed. Basal and stimulated cortisol concentrations, DHEAS, and plasma renin activity (PRA) were measured. A cortisol response post-ACTH below 18 µg/dL was considered abnormal.

RESULTS

58% of the tested patients had an abnormal response to ACTH test. These patients also had lower DHEAS concentrations, but were not different in diabetes duration, HbA1C, severe hypoglycemia, ACTH, or PRA concentrations compared to those who had a normal cortisol post-ACTH. One patient out of 59, had a positive anti-21-hydroxylase antibody (21OHA) and presented a poor response to ACTH.

CONCLUSIONS

We found a significant proportion of our patients having a subnormal cortisol response independent of the presence of anti-adrenal cell antibodies. We did not find a correlation with metabolic control, probably due to the good metabolic control of this group. The absence of 21OHA does not rule out subclinical hypocortisolism in this population. Our results suggest testing adrenal function in children with DM1.

Glucocorticoids are Gastroprotective under Physiologic Conditions

Stress may contribute to the development and progression of gastrointestinal disorders. Activation of the hypothalamic-pituitary-adrenocortical (HPA) axis is one of the main characteristics of stress. For several decades it was generally accepted that glucocorticoids released during stress are ulcerogenic hormones. We designed some experimental studies in rats to clarify the validity of this widely held view. To achieve this goal, we examined the effect of glucocorticoid deficiency followed by corticosterone replacement or the glucocorticoid receptor antagonist, RU-38486, on stress-induced gastric erosion and the parameters of gastric function in rats. The data obtained shows that the reduction in the stress-induced corticosterone release, or its actions, aggravates stress-caused gastric erosion. It is suggested that an acute increase in corticosterone during stress protects the stomach against stress-induced injury. According to our results, various ulcerogenic stimuli, similar to stress, induce an increase in corticosterone that helps the gastric mucosa to resist against a harmful action of ulcerogenic stimuli. Glucocorticoids exhibit their gastroprotective effect by both maintaining local defensive factors and inhibiting pathogenic elements. Furthermore, the contribution of glucocorticoids to gastroprotection is tightly related to their contribution to general body homeostasis. Glucocorticoids provide gastroprotective actions in co-operation with prosta-glandins, nitric oxide and capsaicin-sensitive sensory neurons. The results obtained do not support the traditional paradigm and suggest that glucocorticoids released during acute activation of the HPA axis are naturally occurring gastroprotective factors. In this article, we review our recent publications on the role of glucocorticoids in gastroprotection.

Differential activations of PKC/PKA related to microvasculopathy in diabetic GK rats

Microvasculopathy is the most serious and predictable threat to the health of diabetic patients, which often results in end-stage renal disease, blindness, and limb amputations. Up to the present, the underlying mechanisms have remained elusive. Here, it was found that the differential activations of PKC/PKA were involved in diabetic microvasculopathy in diabetic GK rats. By real-time PCR, Western blot, immunohistochemistry, and enzyme activity assay, upregulation of PKC was prominent in kidney but was not significant in liver and brain. The expression and activity of PKA were lowered in kidney but comparable in brain and liver during diabetic nephropathy. Furthermore, the generation of reactive oxygen species, production of nitric oxide, and expression of inducible nitric oxide synthase induced by advanced glycation end products were inhibited by PKCβ inhibitor LY-333531 or a PKA agonist in rat glomerular microvascular endothelial cells. Finally, albuminuria was significantly lowered by a PKA agonist and boosted by a PKA antagonist. It suggested that the differential activations of PKC/PKA related to microvasculopathy in diabetes and that activation of PKA may protect the diabetic microvasculature.

Somatostatin receptor type 2 antagonism improves glucagon and corticosterone counterregulatory responses to hypoglycemia in streptozotocin-induced diabetic rats

Diminished responsiveness to hypoglycemia contributes to defective counterregulation in diabetes. Pancreatic and/or circulating somatostatin are elevated in diabetes, which may inhibit counterregulatory hormone release during hypoglycemia. Thus, a selective somatostatin receptor type 2 antagonist (SSTR2a) should improve hormone counterregulation to hypoglycemia. Nondiabetic (N) and streptozotocin-induced diabetic (D) rats underwent 4-h infusion of saline or SSTR2a with insulin-induced hypoglycemia clamped at 2.5 ± 0.5 mmol/L. To evaluate the effect of the SSTR2a in the absence of hypoglycemia, rats underwent a 4-h infusion of saline (Ctrl:N, Ctrl:D) or SSTR2a (Ctrl:D+SSTR2a) only. The attenuated glucagon response to hypoglycemia in D (P < 0.0002) was fully restored by SSTR2a (P < 0.0001). Furthermore, the attenuated corticosterone response in D (P < 0.002) was also enhanced by SSTR2a (P < 0.05). In the absence of hypoglycemia, SSTR2a did not alter basal blood glucose levels. D exhibited 62% more pancreatic somatostatin than N after hypoglycemia. In N rats, SSTR2a did not augment the glucagon or corticosterone response to hypoglycemia. Thus, somatostatin may contribute to impaired glucagon responsiveness to hypoglycemia in diabetes. We demonstrate that SSTR2 antagonism enhances hypoglycemia-stimulated glucagon and corticosterone release in D but not in N rats. SSTR2 antagonism does not affect basal glycemia in D rats.

Voluntary physical activity and leucine correct impairments in muscle protein synthesis in partially pancreatectomised rats

AIMS/HYPOTHESIS

Poorly controlled type 1 diabetes mellitus can cause reduced skeletal muscle mass and weakness during adolescence, which may affect long-term management of the disease. The aim of this study was to determine whether regular voluntary physical activity and leucine feeding restore rates of protein synthesis and deficits in skeletal muscle mass in a young, hypoinsulinaemic/hyperglycaemic rat model of diabetes.

METHODS

Four-week-old male Sprague-Dawley rats were partially pancreatectomised (Px) to induce hypoinsulinaemia/hyperglycaemia and housed with/without access to running wheels for 3 weeks (n = 12-14/group). Sham surgery rats (shams) served as sedentary controls (n = 18). Protein synthesis and markers of protein anabolism were assessed in the fasted state and following leucine gavage. Fibre type and cross-sectional areas of the gastrocnemius muscle were measured using a metachromatic ATPase stain.

RESULTS

Compared with sedentary behaviour, regular activity lowered fasting glycaemia and reduced fed hyperglycaemia in Px rats. Active-Px rats, which ran 2.2  ±  0.71 km/night, displayed greater muscle mass and fibre areas similar to shams, while sedentary-Px rats displayed a 20-30% loss in muscle fibre areas. Muscle protein synthesis (basal and in response to leucine gavage) was impaired in sedentary-Px (by ~65%), but not in active-Px rats, when compared with shams. Following leucine gavage, the phosphorylation status of eIF4E binding protein 1 (4E-BP1) and ribosomal S6 kinase 1 (S6K1), markers of mammalian target of rapamycin complex 1 (mTORC1) signalling, increased in shams (by two- and ninefold, respectively) and in active-Px (1.5- and fourfold, respectively) rats, but not in sedentary-Px rats.

CONCLUSION/INTERPRETATION

Moderate physical activity in young Px rats normalises impairments in skeletal muscle growth and protein synthesis. These findings illustrate the critical compensatory role that modest physical activity and targeted nutrition can have on skeletal muscle growth during periods of hypoinsulinaemia in adolescent diabetes.

Effects of ghrelin, growth hormone-releasing peptide-6, and growth hormone-releasing hormone on growth hormone, adrenocorticotropic hormone, and cortisol release in type 1 diabetes mellitus

In type 1 diabetes mellitus (T1DM), growth hormone (GH) responses to provocative stimuli are normal or exaggerated, whereas the hypothalamic-pituitary-adrenal axis has been less studied. Ghrelin is a GH secretagogue that also increases adrenocorticotropic hormone (ACTH) and cortisol levels, similarly to GH-releasing peptide-6 (GHRP-6). Ghrelin's effects in patients with T1DM have not been evaluated. We therefore studied GH, ACTH, and cortisol responses to ghrelin and GHRP-6 in 9 patients with T1DM and 9 control subjects. The GH-releasing hormone (GHRH)-induced GH release was also evaluated. Mean fasting GH levels (micrograms per liter) were higher in T1DM (3.5 ± 1.2) than in controls (0.6 ± 0.3). In both groups, ghrelin-induced GH release was higher than that after GHRP-6 and GHRH. When analyzing Δ area under the curve (ΔAUC) GH values after ghrelin, GHRP-6, and GHRH, no significant differences were observed in T1DM compared with controls. There was a trend (P = .055) to higher mean basal cortisol values (micrograms per deciliter) in T1DM (11.7 ± 1.5) compared with controls (8.2 ± 0.8). No significant differences were seen in ΔAUC cortisol values in both groups after ghrelin and GHRP-6. Mean fasting ACTH values were similar in T1DM and controls. No differences were seen in ΔAUC ACTH levels in both groups after ghrelin and GHRP-6. In summary, patients with T1DM have normal GH responsiveness to ghrelin, GHRP-6, and GHRH. The ACTH and cortisol release after ghrelin and GHRP-6 is also similar to controls. Our results suggest that chronic hyperglycemia of T1DM does not interfere with GH-, ACTH-, and cortisol-releasing mechanisms stimulated by these peptides.

Brain insulin action regulates hypothalamic glucose sensing and the counterregulatory response to hypoglycemia

OBJECTIVE

An impaired ability to sense and appropriately respond to insulin-induced hypoglycemia is a common and serious complication faced by insulin-treated diabetic patients. This study tests the hypothesis that insulin acts directly in the brain to regulate critical glucose-sensing neurons in the hypothalamus to mediate the counterregulatory response to hypoglycemia.

RESEARCH DESIGN AND METHODS

To delineate insulin actions in the brain, neuron-specific insulin receptor knockout (NIRKO) mice and littermate controls were subjected to graded hypoglycemic (100, 70, 50, and 30 mg/dl) hyperinsulinemic (20 mU/kg/min) clamps and nonhypoglycemic stressors (e.g., restraint, heat). Subsequently, counterregulatory responses, hypothalamic neuronal activation (with transcriptional marker c-fos), and regional brain glucose uptake (via (14)C-2deoxyglucose autoradiography) were measured. Additionally, electrophysiological activity of individual glucose-inhibited neurons and hypothalamic glucose sensing protein expression (GLUTs, glucokinase) were measured.

RESULTS

NIRKO mice revealed a glycemia-dependent impairment in the sympathoadrenal response to hypoglycemia and demonstrated markedly reduced (3-fold) hypothalamic c-fos activation in response to hypoglycemia but not other stressors. Glucose-inhibited neurons in the ventromedial hypothalamus of NIRKO mice displayed significantly blunted glucose responsiveness (membrane potential and input resistance responses were blunted 66 and 80%, respectively). Further, hypothalamic expression of the insulin-responsive GLUT 4, but not glucokinase, was reduced by 30% in NIRKO mice while regional brain glucose uptake remained unaltered.

CONCLUSIONS

Chronically, insulin acts in the brain to regulate the counterregulatory response to hypoglycemia by directly altering glucose sensing in hypothalamic neurons and shifting the glycemic levels necessary to elicit a normal sympathoadrenal response.

Regular exercise prevents the development of hyperglucocorticoidemia via adaptations in the brain and adrenal glands in male Zucker diabetic fatty rats

We determined the effects of voluntary wheel running on the hypothalamic-pituitary-adrenal (HPA) axis, and the peripheral determinants of glucocorticoids action, in male Zucker diabetic fatty (ZDF) rats. Six-week-old euglycemic ZDF rats were divided into Basal, Sedentary, and Exercise groups (n = 8-9 per group). Basal animals were immediately killed, whereas Sedentary and Exercising rats were monitored for 10 wk. Basal (i.e., approximately 0900 AM in the resting state) glucocorticoid levels increased 2.3-fold by week 3 in Sedentary rats where they remained elevated for the duration of the study. After an initial elevation in basal glucocorticoid levels at week 1, Exercise rats maintained low glucocorticoid levels from week 3 through week 10. Hyperglycemia was evident in Sedentary animals by week 7, whereas Exercising animals maintained euglycemia throughout. At the time of death, the Sedentary group had approximately 40% lower glucocorticoid receptor (GR) content in the hippocampus, compared with the Basal and Exercise groups (P < 0.05), suggesting that the former group had impaired negative feedback regulation of the HPA axis. Both Sedentary and Exercise groups had elevated ACTH compared with Basal rats, indicating that central drive of the axis was similar between groups. However, Sedentary, but not Exercise, animals had elevated adrenal ACTH receptor and steroidogenic acute regulatory protein content compared with the Basal animals, suggesting that regular exercise protects against elevations in glucocorticoids by a downregulation of adrenal sensitivity to ACTH. GR and 11beta-hydroxysteroid dehydrogenase type 1 content in skeletal muscle and liver were similar between groups, however, GR content in adipose tissue was elevated in the Sedentary groups compared with the Basal and Exercise (P < 0.05) groups. Thus, the gradual elevations in glucocorticoid levels associated with the development of insulin resistance in male ZDF rats can be prevented with regular exercise, likely because of adaptations that occur primarily in the adrenal glands.

Functional state of adrenocortical system in rats with manifest alloxan-induced diabetes mellitus

In the adrenals of male rats with manifest form of alloxan-induced diabetes mellitus (blood glucose >20 mmol/liter), the content of progesterone was higher by 1.6 times, deoxycorticosterone by 2.5 times, corticosterone by 3.3 times, and 11-dehydrocorticosterone by 1.8 times than in the adrenals of control animals. Increased concentration of corticosterone and 11-dehydrocorticosterone were also found in the serum of rats with alloxan diabetes, but the difference between the experimental and control groups by these parameters was less pronounced compared to parameters in the adrenal glands.

Shaping the stress response: interplay of palatable food choices, glucocorticoids, insulin and abdominal obesity

Activity of the hypothalamo-pituitary-adrenal (HPA) axis is regulated by a negative feedback loop that dampens central drive of the axis via the actions of the secreted glucocorticoids. Conversely, under conditions of chronic stress, glucocorticoids delivered centrally increase hypothalamic paraventricular nucleus (PVN) corticotrophin-releasing factor (CRF) expression and the response to restraint. However, HPA axis activity and PVN CRF mRNA expression under chronic stress conditions are often reduced, implying other indirect peripheral or extra-hypothalamic glucocorticoid actions. Glucocorticoids chronically increase palatable food intake, which increases abdominal fat depots and circulating insulin levels, both of which negatively correlate with PVN CRF mRNA expression and may in turn dampen the response to stress. Such an effect is dependent on food choices, rather than total calories ingested. Considering stress is omnipresent in the workplace, palatable food ingestion may represent a means to combat the feeling of stress which is ultimately maladaptive when unresolved.

Inflammation and neuropeptides: the connection in diabetic wound healing

Abnormal wound healing is a major complication of both type 1 and type 2 diabetes, with nonhealing foot ulcerations leading in the worst cases to lower-limb amputation. Wound healing requires the integration of complex cellular and molecular events in successive phases of inflammation, cell proliferation, cell migration, angiogenesis and re-epithelialisation. A link between wound healing and the nervous system is clinically apparent as peripheral neuropathy is reported in 30-50% of diabetic patients and is the most common and sensitive predictor of foot ulceration. Indeed, a bidirectional connection between the nervous and the immune systems and its role in wound repair has emerged as one of the focal features of the wound-healing dogma. This review provides a broad overview of the mediators of this connection, which include neuropeptides and cytokines released from nerve fibres, immune cells and cutaneous cells. In-depth understanding of the signalling pathways in the neuroimmune axis in diabetic wound healing is vital to the development of successful wound-healing therapies.

The effect of long-term insulin treatment with and without antecedent hypoglycemia on neuropeptide and corticosteroid receptor expression in the brains of diabetic rats

We previously demonstrated that while diabetic animals receiving long-term insulin treatment exhibited some impairment in their corticosterone response to hypoglycemia, the stress response to hypoglycemia was completely absent when these animals were subjected to recurrent hypoglycemia. In the current study, we examined potential mechanisms that may contribute to defects in the adrenocortical response to hypoglycemia in long-term insulin-treated diabetic animals exposed to antecedent hypoglycemia. Whereas insulin-treated diabetic animals exhibited a significant rise in corticotrophin-releasing hormone (CRH) mRNA levels during hypoglycemia, exposure to antecedent hypoglycemia completely abolished this response. Moreover, expression of hippocampal mineralocorticoid receptors (MR) mRNA, which normally act to suppress hypothalamo-pituitary-adrenal activity, decreased in the normal control and insulin-treated diabetic groups in response to hypoglycemia, whereas MR mRNA levels remained at baseline in animals subjected to antecedent hypoglycemia. Interestingly, hippocampal glucocorticoid receptor (GR) mRNA levels decreased in all three treatment groups following the hypoglycemic clamp. While GR mRNA levels in the paraventricular nucleus were lower in normal controls following hypoglycemia, this trend just failed to reach statistical significance in the two diabetic groups. These data suggest that (1) recurrent hypoglycemia, much like uncontrolled diabetes, has a pronounced effect on hippocampal mineralocorticoid receptor mRNA expression that may prevent it, and presumably also the stress axis, from responding properly to a subsequent bout of hypoglycemia, and (2) while long-term insulin treatment was sufficient to restore some of these responses in diabetic animals, tighter glycemic control may be necessary to see full restoration of the stress response.

Stimulation of both type I and type II corticosteroid receptors blunts counterregulatory responses to subsequent hypoglycemia in healthy man

Antecedent increases of corticosteroids can blunt counterregulatory responses to subsequent stress. Our aim was to determine whether prior activation of type I corticosteroid (mineralocorticoid) or type II corticosteroid (glucocorticoid) receptors blunts counterregulatory responses to subsequent hypoglycemia. Healthy volunteers participated in five randomized 2-day protocols. Day 1 involved morning and afternoon 2-h hyperinsulinemic (9 pmol.kg(-1).min(-1)) euglycemic clamps (PE; n = 14), hypoglycemic clamps (PH; n = 14), or euglycemic clamps with oral fludrocortisone (PE + F; type I agonist, 0.2 mg, n = 14), oral dexamethasone (PE + D; type II agonist, 0.75 mg, n = 13), or both (PE + F + D; n = 14). Day 2 was identical in all protocols and consisted of a 2-h hyperinsulinemic hypoglycemic clamp. Day 2 insulin (625 +/- 40 pmol/l) and glucose (2.9 +/- 0.1 mmol/l) levels were similar among groups. Levels of epinephrine, norepinephrine, glucagon, growth hormone, and MSNA were significantly blunted by prior activation of both type I and type II corticosteroid receptors to PE. Prior activation of both corticosteroid receptors also significantly blunted NEFA during subsequent hypoglycemia. Thus, levels of a wide spectrum of key counterregulatory mechanisms (neuroendocrine, ANS, and metabolic) were blunted by antecedent pharmacological stimulation of either type I or type II corticosteroid receptors in healthy man. These data suggest that activation of type I corticosteroid receptors in man can have acute and profound regulating effects on physiological stress in man. Both type I and type II corticosteroid receptors may be involved in the multiple mechanisms controlling counterregulatory responses to hypoglycemia in healthy man.

Corticosterone inhibits the lipid-mobilizing effects of oleoyl-estrone in adrenalectomized rats

Oleoyl-estrone (OE) is an adipose-derived signal that decreases energy intake and body lipid, maintaining energy expenditure and glycemic homeostasis. Glucocorticoids protect body lipid and the metabolic status quo. We studied the combined effects of OE and corticosterone in adrenalectomized female rats: daily OE gavages (0 or 10 nmol/g) and slow-release corticosterone pellets at four doses (0, 0.5, 1.7, and 4.8 mg/d). Intact and sham-operated controls were also included. After 8 d, body composition and plasma metabolites and hormones were measured. OE induced a massive lipid mobilization (in parallel with decreased food intake and maintained energy expenditure). Corticosterone increased fat deposition and inhibited the OE-elicited mobilization of body energy, even at the lowest dose. OE enhanced the corticosterone-induced rise in plasma triacylglycerols, and corticosterone blocked the OE-induced decrease in leptin. High corticosterone and OE increased insulin resistance beyond the effects of corticosterone alone. The presence of corticosterone dramatically affected OE effects, reversing its decrease of body energy (lipid) content, with little or no change on food intake or energy expenditure. The maintenance of glycemia and increasing insulin in parallel to the dose of corticosterone indicate a decrease in insulin sensitivity, which is enhanced by OE. The reversal of OE effects on lipid handling, insulin resistance, can be the consequence of a corticosterone-induced OE resistance. Nevertheless, OE effects on cholesterol were largely unaffected. In conclusion, corticosterone administration effectively blocked OE effects on body lipid and energy balance as well as insulin sensitivity and glycemia.

Gastroprotective role of glucocorticoid hormones

Gastric ulcer disease remains widespread; a stressful lifestyle and nonsteroidal antiinflammatory drugs (NSAIDs) make significant contributions to this pathological situation. The findings overviewed here support the idea that glucocorticoid hormones released in response to acute stress or NSAIDs act as gastroprotective substances and exert many of the same actions in the stomach as prostaglandins (PGs) and nitric oxide (NO) as well as capsaicin-sensitive afferent neurons. Glucocorticoids exert a gastroprotective effect by both maintaining local defensive factors (mucosal blood flow and mucus production) and inhibiting pathogenic elements (gastric motility and microvascular permeability). Furthermore, they exert gastroprotective actions in co-operation with PGs, NO, and the afferent neurons; and their compensatory action is observed when the protective mechanism provided by either of these factors is impaired. The gastroprotective action of glucocorticoids is also associated with maintenance of general body homeostasis, including blood glucose levels and systemic blood pressure. In conclusion, glucocorticoids released in response to acute stress or NSAIDs are naturally occurring protective factors that play an important role in maintenance of the gastric mucosal integrity. This led us to re-evaluate the traditional paradigm that glucocorticoid hormones produced during activation of the hypothalamic-pituitary-adrenocortical axis are ulcerogenic in the stomach.

Progesterone and its derivatives are neuroprotective agents in experimental diabetic neuropathy: a multimodal analysis

One important complication of diabetes is damage to the peripheral nervous system. However, in spite of the number of studies on human and experimental diabetic neuropathy, the current therapeutic arsenal is meagre. Consequently, the search for substances to protect the nervous system from the degenerative effects of diabetes has high priority in biomedical research. Neuroactive steroids might be interesting since they have been recently identified as promising neuroprotective agents in several models of neurodegeneration. We have assessed whether chronic treatment with progesterone (P), dihydroprogesterone (DHP) or tetrahydroprogesterone (THP) had neuroprotective effects against streptozotocin (STZ)-induced diabetic neuropathy at the neurophysiological, functional, biochemical and neuropathological levels. Using gas chromatography coupled to mass-spectrometry, we found that three months of diabetes markedly lowered P plasma levels in male rats, and chronic treatment with P restored them, with protective effects on peripheral nerves. In the model of STZ-induced of diabetic neuropathy, chronic treatment for 1 month with P, or with its derivatives, DHP and THP, counteracted the impairment of nerve conduction velocity (NCV) and thermal threshold, restored skin innervation density, and improved Na(+),K(+)-ATPase activity and mRNA levels of myelin proteins, such as glycoprotein zero and peripheral myelin protein 22, suggesting that these neuroactive steroids, might be useful protective agents in diabetic neuropathy. Interestingly, different receptors seem to be involved in these effects. Thus, while the expression of myelin proteins and Na(+),K(+)-ATPase activity are only stimulated by P and DHP (i.e. two neuroactive steroids interacting with P receptor, PR), NCV, thermal nociceptive threshold and intra-epidermal nerve fiber (IENF) density are also affected by THP, which interacts with GABA-A receptor. Because, a therapeutic approach with specific synthetic receptor ligands could avoid the typical side effects of steroids, future experiments will be devoted to evaluating the role of PR and GABA-A receptor in these protective effects.

Diabetes-induced changes in the alternative splicing of the slo gene in corporal tissue

OBJECTIVES

Erectile dysfunction is a common diabetic complication. Preclinical studies have documented that the Slo gene (encoding the BK or Maxi-K channel alpha-subunit) plays a critical role in erectile function. Therefore, we determined whether diabetes induces changes in the splicing of the Slo gene relevant to erectile function.

METHODS

Reverse transcriptase-polymerase chain reaction was used to compare Slo splice variant expression in corporal tissue excised from control and streptozotocin (STZ)-induced diabetic Fischer F-344 rats. Splice variants were sequenced, characterized by patch clamping, and fused to green fluorescent protein to determine cellular localization. The impact of altered Slo expression on erectile function was further evaluated in vivo.

RESULTS

A novel Slo splice variant (SVcyt, with a cytoplasmic location) was predominantly expressed in corporal tissue from control rats. STZ-diabetes caused upregulation of a channel-forming transcript SV0. Preliminary results suggest that SV0 was also more prevalent in the corporal tissue of human diabetic compared with nondiabetic patients. The change in isoform expression in STZ-treated rats was partially reversed by insulin treatment. Intracorporal injection of a plasmid expressing the SV0 transcript, but not SVcyt, restored erectile function in STZ-diabetic rats.

CONCLUSIONS

Alternative splicing of the Slo transcript may represent an important compensatory mechanism to increase the ease with which relaxation of corporal tissue may be triggered as a result of a diabetes-related decline in erectile capacity.

Hypoglycemia, an Old Tool for New Findings in the Adrenomedullary Hormonal System in Patients with Rheumatic Diseases

Over the past decades, research in patients with rheumatic disorders showed enormous progress in detecting various perturbations of the neuroendocrine system including those affecting autonomic nervous function. There is, however, a substantial lack of data on adrenomedullary hormonal system (AMHS) function in those patients. Insulin-induced hypoglycemia (IIH) represents a metabolic stressor, which elicits a counterregulatory stress response not only of the hypothalamic-pituitary axis but also of the AMHS. Therefore, in addition to traditional testing of hypothalamic-pituitary function, IIH can be used as a well-controlled functional test of the AMHS. Our recent studies showed, for the first time, attenuated epinephrine and norepinephrine responses to IIH in premenopausal females with rheumatoid arthritis (RA) and systemic sclerosis (SSc). These findings are suggestive of downregulation, or possibly defects, of the AMHS in those patients. This article reviews mechanism of the AMHS activation during IIH and demonstrates applications of the test in neuroendocrine-immune research.

Gastroprotective action of glucocorticoid hormones in rats with desensitization of capsaicin-sensitive sensory neurons

The ability of glucocorticoid hormones to protect gastric mucosa during desensitization of capsaicin-sensitive afferent neurons has been investigated in rats. Functional ablation of the afferent neurons was performed by pre-treatment with neurotoxic doses of capsaicin (100 mg/kg s.c.). After 1 week of recovery, capsaicin-desensitized, as well as control rats were adrenalectomized or sham-operated. Seven days later, indomethacin at an ulcerogenic dose (35 mg/kg s.c.) was given to each group of rats. One half of adrenalectomized capsaicin-pre-treated rats were injected by corticosterone for replacement (4 mg/kg s.c., 15 min before indomethacin). Gastric lesions, plasma corticosterone and blood glucose levels were estimated 4 h after indomethacin administration. Indomethacin caused gastric erosions that were aggravated by adrenalectomy or desensitization of capsaicin-sensitive afferent neurons approximately with the same extension. Combination of adrenalectomy with the sensory desensitization profoundly potentiated the effect of sensory desensitization alone on indomethacin-induced gastric erosions: the mean gastric erosion area was increased approximately 10-fold. Corticosterone replacement completely prevented this profound effect of adrenalectomy. The results suggest a pivotal role of glucocorticoid hormones in the maintenance of gastric mucosal integrity in the case of impaired gastroprotective mechanisms provided by PGs and capsaicin-sensitive sensory neurons.

Blockade of GABA(A) receptors in the ventromedial hypothalamus further stimulates glucagon and sympathoadrenal but not the hypothalamo-pituitary-adrenal response to hypoglycemia

Hypoglycemia provokes a multifaceted counterregulatory response involving the sympathoadrenal system, stimulation of glucagon secretion, and the hypothalamo-pituitary-adrenal axis that is commonly impaired in diabetes. We examined whether modulation of inhibitory input from gamma-aminobutyric acid (GABA) in the ventromedial hypothalamus (VMH), a major glucose-sensing region within the brain, plays a role in affecting counterregulatory responses to hypoglycemia. Normal Sprague-Dawley rats had carotid artery and jugular vein catheters chronically implanted, as well as bilateral steel microinjection guide cannulas inserted down to the level of the VMH. Seven to 10 days following surgery, the rats were microinjected with artificial extracellular fluid, the GABA(A) receptor agonist muscimol (1 nmol/side), or the GABA(A) receptor antagonist bicuculline methiodide (12.5 pmol/side) before being subjected to a hyperinsulinemic-hypoglycemic (2.5 mmol/l) glucose clamp for 90 min. Following VMH administration of bicuculline methiodide, glucose infusion rates were significantly suppressed, whereas muscimol raised glucose infusion rates significantly compared with controls. Glucagon and epinephrine responses were elevated with the antagonist and suppressed with the agonist compared with controls. Corticosterone responses, however, were unaffected by either administration of the agonist or antagonist into the VMH. These data demonstrate that modulation of the GABAergic system in the VMH alters both glucagon and sympathoadrenal, but not corticosterone, responses to hypoglycemia. Our findings are consistent with the hypothesis that GABAergic inhibitory tone within the VMH can modulate glucose counterregulatory responses.

Effects of insulin treatment without and with recurrent hypoglycemia on hypoglycemic counterregulation and adrenal catecholamine-synthesizing enzymes in diabetic rats

Untreated diabetic rats show impaired counterregulation against hypoglycemia. The blunted epinephrine responses are associated with reduced adrenomedullary tyrosine hydroxylase (TH) mRNA levels. Recurrent hypoglycemia further impairs epinephrine counterregulation and is also associated with reduced phenylethanolamine N-methyltransferase mRNA. This study investigated the adaptations underlying impaired counterregulation in insulin-treated diabetic rats, a more clinically relevant model. We studied the effects of insulin treatment on counterregulatory hormones and adrenal catecholamine-synthesizing enzymes and adaptations after recurrent hypoglycemia. Groups included: normal; diabetic, insulin-treated for 3 wk (DI); and insulin-treated diabetic exposed to seven episodes (over 4 d) of hyperinsulinemic-hypoglycemia (DI-hypo) or hyperinsulinemic-hyperglycemia (DI-hyper). DI-hyper rats differentiated the effects of hyperinsulinemia from those of hypoglycemia. On d 5, rats from all groups were assessed for adrenal catecholamine-synthesizing enzyme levels or underwent hypoglycemic clamps to examine counterregulatory responses. Despite insulin treatment, fasting corticosterone levels remained increased, and corticosterone responses to hypoglycemia were impaired in DI rats. However, glucagon, epinephrine, norepinephrine, and ACTH counterregulatory defects were prevented. Recurrent hypoglycemia in DI-hypo rats blunted corticosterone but, surprisingly, not epinephrine responses. Norepinephrine and ACTH responses also were not impaired, whereas glucagon counterregulation was reduced due to repeated hyperinsulinemia. Insulin treatment prevented decreases in basal TH protein and increased PNMT and dopamine beta-hydroxylase protein. DI-hypo rats showed increases in TH, PNMT, and dopamine beta-hydroxylase. We conclude that insulin treatment of diabetic rats protects against most counterregulatory defects but not elevated fasting corticosterone and decreased corticosterone counterregulation. Protection against epinephrine defects, both without and with antecedent hypoglycemia, is associated with enhancement of adrenal catecholamine-synthesizing enzyme levels.

Hypothalamic paraventricular nucleus, but not vasopressin, participates in chronic hyperactivity of the HPA axis in diabetic rats

Diabetes mellitus (DM), as chronic stress activates the hypothalamo-pituitary-adrenocortical axis. We examined whether arginine vasopressin (AVP) and the hypothalamic paraventricular nucleus (PVN) participate in DM-induced chronic stress symptoms. AVP-deficient Brattleboro or PVN-lesioned Wistar rats were used with heterozygous or sham-operated controls. The rats were studied 2 wk after a single injection of streptozotocin. The appearance of DM (enhanced water consumption and blood glucose elevation) and the chronic stress-like somatic changes (body weight decrease, thymus involution, adrenal gland hypertrophy) were not influenced by the lack of AVP. By contrast, PVN lesion significantly attenuated DM-induced thymus involution and adrenal gland hypertrophy as well as the increase in water consumption. The corticotropin-releasing hormone mRNA in PVN was diminished by DM and elevated by the lack of AVP without interaction. DM elevated the proopiomelanocortin (POMC) mRNA in the anterior lobe of the pituitary. The lack of AVP had no effect, whereas lesioning the PVN significantly diminished the elevation. The elevated basal corticosterone plasma levels detectable in DM were influenced neither by the lack of AVP nor by lesioning the PVN. Thus the lack of AVP had no influence on DM-induced chronic stress symptoms, but lesioning the PVN attenuated part of them. However, the lack of elevation in POMC mRNA after PVN lesion, together with the maintained corticosterone elevation, suggests that direct adrenal gland activation occurs in untreated DM.

The role of vasopressin in diabetes mellitus-induced hypothalamo-pituitary-adrenal axis activation: studies in Brattleboro rats

Chronic diabetes mellitus (DM) induces hyperactivity of the hypothalamo-pituitary-adrenal axis (HPA). Our present study addresses the role of vasopressin (AVP) in maintaining adrenocortical responsiveness during DM. AVP-deficient mutant Brattleboro rats were used with heterozygous controls and the V2 agonist, desmopressin was infused to replace peripheral AVP. To induce DM the rats were injected by streptozotocin (STZ, 60 mg/ml/kg i.v.) and studied 2 weeks later. The acute stress stimulus was 60 min restraint. The signs of DM (the increase in water consumption and in blood glucose levels) were discovered in all rats. The diuretic effect of the lack of AVP was additional to the DM-induced osmotic diuresis. DM induced significant, chronic stress-like somatic changes on which AVP-deficiency had no effect and although desmopressin infusion normalized the water consumption and the body weight gain in AVP-deficient rats, it had no effect on DM-induced changes. The acute stress-induced plasma ACTH elevation was smaller in AVP-deficient or DM rats but these effects were not additive. Desmopressin did not normalize the decreased ACTH-elevation of AVP-deficient animals. The resting morning plasma corticosterone level was elevated both in DM and AVP-deficient rats without interaction. The restraint-induced corticosterone rise was influenced neither by the lack of AVP nor by DM and the basal and stress-induced prolactin levels were smaller in DM rats without any effect of AVP-deficiency. In conclusion, our data suggest that AVP does not play a crucial role in HPA axis regulation during DM-induced chronic stress. In contrast, the role of AVP seems to be more important during acute stress, however, it is restricted to the ACTH regulation. According to the water consumption data diabetes insipidus seems to be an additional risk factor for DM.