Regulatory mechanism of hypothalamo-pituitary-adrenal (HPA) axis and neuronal changes after adrenalectomy in type 2 diabetes

Scientometric analysis and historical review of diabetic encephalopathy research: Trends and hotspots (2004-2023)

BACKGROUND

Diabetic encephalopathy (DE) is a common and serious complication of diabetes that can cause death in many patients and significantly affects the lives of individuals and society. Multiple studies investigating the pathogenesis of DE have been reported. However, few studies have focused on scientometric analysis of DE.

AIM

To analyze literature on DE using scientometrics to provide a comprehensive picture of research directions and progress in this field.

METHODS

We reviewed studies on DE or cognitive impairment published between 2004 and 2023. The latter were used to identify the most frequent keywords in the keyword analysis and explore the hotspots and trends of DE.

RESULTS

Scientometric analysis revealed 1308 research papers on DE, a number that increased annually over the past 20 years, and that the primary topics explored were domain distribution, knowledge structure, evolution, and emergence of research topics related to DE. The inducing factors, comorbidities, pathogenesis, treatment, and animal models of DE help clarify its occurrence, development, and treatment. An increasing number of studies on DE may be a result of the recent increase in patients with diabetes, unhealthy lifestyles, and unhealthy eating habits, which have aggravated the incidence of this disease.

CONCLUSION

We identified the main inducing factors and comorbidities of DE, though other complex factors undoubtedly increase social and economic burdens. These findings provide vital references for future studies.

Hypercorticosteronemia induces hyperphagia and obesity in human growth hormone transgenic rats

Hyperphagia and subsequent obesity are important public health issues due to the associated risks of developing serious diseases. Certain stressors play a major role in the development of hyperphagia. In previous studies, we established a line of human growth hormone transgenic (TG) rats that exhibit hyperphagia and obesity from a young age. We recently demonstrated that voluntary running on a running wheel alleviates hyperphagia in TG rats. Wheel running provides environmental enrichment for rodents and plays a role in relieving stress. These results suggested that stress is the major factor inducing hyperphagia in TG rats. Thus, in the present study, we evaluated activation of the hypothalamus-pituitary-adrenal axis. TG rats showed bilateral enlargement of adrenal glands and hypercorticosteronemia, although their hypothalamic CRH level was comparable to that of wild-type (WT) rats. The ACTH-immunoreactive area was larger and the serum ACTH level in the dark phase was higher in TG rats than in WT rats. Adrenalectomy reduced the food intake of TG rats to a level comparable to that in WT rats, and supplying glucocorticoids recurred hyperphagia in TG rats. These treatments did not affect the food intake of WT rats. Rearing TG rats under group housing prevented hyperphagia and hypercorticosteronemia. These results suggest that glucocorticoids are appetite stimulants, and that TG rats exhibit increased sensitivity to the appetite-stimulating effect of glucocorticoids.

Effects of Saffron Extract (Affron®) with 100 mg/kg and 200 mg/kg on Hypothalamic-Pituitary-Adrenal Axis and Stress Resilience in Chronic Mild Stress-Induced Depression in Wistar Rats

Stress-related symptoms are a global concern, impacting millions of individuals, yet effective and safe treatments remain scarce. Although multiple studies have highlighted the stress- alleviating properties of saffron extract, the underlying mechanisms remain unclear. This study employs the unpredictable chronic mild stress (CMS) animal model to investigate the impact of a standardized saffron extract, Affron® (AFN), on hypothalamic-pituitary-adrenal (HPA) axis regulation and neuroplasticity in Wistar rats following repeated oral administration. The research evaluates AFN's effects on various stress-related parameters, including hypothalamic gene expression, stress hormone levels, and the sucrose preference test. In animals subjected to continuous unpredictable CMS, repetitive administration of AFN at doses of 100 mg/kg and 200 mg/kg effectively normalized HPA axis dysregulation and enhanced neuroplasticity. Increased concentrations of AFN demonstrated greater efficacy. Following AFN oral administration, adrenocorticotropic and corticosterone hormone levels exhibited significant or nearly significant reductions in comparison to subjects exposed to stress only. These changes align with the alleviation of stress and the normalization of the HPA axis. These findings elucidate AFN's role in stress mitigation, affirm its health benefits, validate its potential as a treatment for stress-related symptoms, confirm its physiological effectiveness, and emphasize its therapeutic promise.

Is metformin neuroprotective against diabetes mellitus-induced neurodegeneration? An updated graphical review of molecular basis

Diabetes mellitus (DM) is a metabolic disease that activates several molecular pathways involved in neurodegenerative disorders. Metformin, an anti-hyperglycemic drug used for treating DM, has the potential to exert a significant neuroprotective role against the detrimental effects of DM. This review discusses recent clinical and laboratory studies investigating the neuroprotective properties of metformin against DM-induced neurodegeneration and the roles of various molecular pathways, including mitochondrial dysfunction, oxidative stress, inflammation, apoptosis, and its related cascades. A literature search was conducted from January 2000 to December 2022 using multiple databases including Web of Science, Wiley, Springer, PubMed, Elsevier Science Direct, Google Scholar, the Core Collection, Scopus, and the Cochrane Library to collect and evaluate peer-reviewed literature regarding the neuroprotective role of metformin against DM-induced neurodegenerative events. The literature search supports the conclusion that metformin is neuroprotective against DM-induced neuronal cell degeneration in both peripheral and central nervous systems, and this effect is likely mediated via modulation of oxidative stress, inflammation, and cell death pathways.

Depression with Comorbid Diabetes: What Evidence Exists for Treatments Using Traditional Chinese Medicine and Natural Products?

Comorbidity between diabetes mellitus (DM) and depression, two chronic and devastating diseases spreading worldwide, has been confirmed by a large body of epidemiological and clinical studies. Due to the bidirectional relationship between DM and depression, this comorbidity leads to poorer outcomes in both conditions. Given the adverse effects and limited effectiveness of the existing therapies for depression associated with diabetes, the development of novel therapeutic drugs with more potency and fewer side effects is still the most important goal. Hence, many researchers have made great efforts to investigate the potential usefulness of traditional Chinese medicine (TCM) and natural products, including natural extracts and purified compounds, in the treatment of comorbid depression in diabetes. Here, we reviewed the related literature on TCM and natural products that can remedy the comorbidity of diabetes and depression and presented them on the basis of their mechanism of action, focusing on shared risk factors, including insulin resistance, oxidative stress and inflammation, and nervous disturbances. In short, this review suggests that TCM and natural products could expand the therapeutic alternatives to ameliorate the association between DM and depressive disorders.

Improvement in neurogenesis and memory function by administration of Passiflora incarnata L. extract applied to sleep disorder in rodent models

Recently, there have been reports that chronic insomnia acts as an insult in the brain, causing memory loss through the production of ROS, inflammation, and, Alzheimer's disease if persistent. Insomnia remains the leading cause of sleep disturbance and as such has serious implications for public health. Patients with Alzheimer's disease are also known to suffer from severe sleep disturbance. Meanwhile, vitexin is a key ingredient in Passiflora incarnata L (passion flower, PF) extract, which is known to help with sleep. This medicinal plant has been used as a folk remedy for sedation, anxiety and sleep since centuries ago, but the standardization work has not been done and the extent of the effect has not been clearly demonstrated. For this reason, we tried to test the possibility that repeated administration of PF could improve the memory by promoting hippocampal neurogenesis at the DBA/2 mice known have inherited sleep disorders, as well as preventive effects of Alzheimer's disease. Here, we found that vitexin, which is the main bioactive component of ethanol extracts from leaves and fruits (ratio; 8:2) of PF, confirmed the improvement of neurogenesis (DCX) of DBA/2 mice repeated PF oral administration by immunohistochemistry (IHC) and western blot analysis. PF-treated group showed increased the neurotrophic factor (BDNF) in the hippocampus compared with that of vehicle-treated group, but the inflammation markers Iba-1 (microglial marker) and COX-2 were inconsistent between the groups. However, we found COX-2 signal is essential for hippocampal neurogenesis according to the additional IHC experiments using COX-2 inhibitor and pIkappaB have shown. In addition, although prescription sleeping pills have been reported to show significant changes in appetite and metabolic rate from time to time, no changes in the feeding behavior, body weight, metabolic rate and body composition of the animals were observed by administration of PF. Interestingly, we found that short-term oral administration of PF displayed improved memory according to the water maze test. Quantitative analysis of Tau protein, which is a marker of Alzheimer's disease, was performed in the SD rats and DBA/2 mice by repeated PF oral administration and pTau/Tau values were significantly decreased in PF-treated group than vehicle-treated group. In conclusion, our results suggest that PF lead high hippocampal neurogenesis in the animals even in inherited sleep-disturbed animals. The increased hippocampal neurogenesis functionally enhanced memory and learning functions by repeated PF oral administration. These results identify PF as a potential therapy for enhancing memory functions and prevention of Alzheimer's disease through actions on the hippocampus.

Shared genetic architecture between metabolic traits and Alzheimer's disease: a large-scale genome-wide cross-trait analysis

A growing number of studies clearly demonstrate a substantial link between metabolic dysfunction and the risk of Alzheimer's disease (AD), especially glucose-related dysfunction; one hypothesis for this comorbidity is the presence of a common genetic etiology. We conducted a large-scale cross-trait GWAS to investigate the genetic overlap between AD and ten metabolic traits. Among all the metabolic traits, fasting glucose, fasting insulin and HDL were found to be genetically associated with AD. Local genetic covariance analysis found that 19q13 region had strong local genetic correlation between AD and T2D (P = 6.78 × 10- 22), LDL (P = 1.74 × 10- 253) and HDL (P = 7.94 × 10- 18). Cross-trait meta-analysis identified 4 loci that were associated with AD and fasting glucose, 3 loci that were associated with AD and fasting insulin, and 20 loci that were associated with AD and HDL (Pmeta < 1.6 × 10- 8, single trait P < 0.05). Functional analysis revealed that the shared genes are enriched in amyloid metabolic process, lipoprotein remodeling and other related biological pathways; also in pancreas, liver, blood and other tissues. Our work identifies common genetic architectures shared between AD and fasting glucose, fasting insulin and HDL, and sheds light on molecular mechanisms underlying the association between metabolic dysregulation and AD.

Endocannabinoid hydrolase and cannabinoid receptor 1 are involved in the regulation of hypothalamus-pituitary-adrenal axis in type 2 diabetes

Hypothalamus-pituitary-adrenal (HPA) axis, as the key moderator in energy metabolism, plays an important role in diabetes. The endogenous cannabinoid system (eCBs) involves in neuronal functions, and simultaneously cannabinoid receptors are almost expressed in all regions of the hypothalamus according to a spate of reports. However, few data investigate the changes of eCBs and HPA axis in type 2 diabetes. In this study, five diabetes mellitus rhesus monkeys, five prediabetes rhesus monkeys and five healthy rhesus monkeys were observed. In the present study, we detected cell swelling and necrosis extensively in the paraventricular nucleus (PVN) and neurohypophysis in prediabetes and overt diabetes monkeys. The adrenocorticotropic hormone in the pituitary gland, adrenocorticotropic hormone receptor, and 11β-hydroxysteroid dehydrogenase in the adrenal gland were all hyper-secreted and expressed from healthy to overt diabetes. Meanwhile, the cortisol concentration in the adrenal gland was increased along with the progress of diabetes. It could be concluded that hyperfunction of the HPA axis exists in the type 2 Diabetes pathogenesis. However, we also found a weakened expression and secretion of corticotrophin releasing hormone and glucocorticoids receptor in PVN. The expression of corticotropin releasing hormone receptor 1 in pituitary gland decreased in prediabetes monkeys, but increased in overt diabetes monkeys. The downregulation of cannabinoid receptor 1 and upregulation of monoglycerol lipase and fatty acid amide hydrolase in PVN was involved in the pathogenesis of type 2 diabetes. Collectively, we can conclude that changes in endocannabinoid hydrolase and cannabinoid receptor might indicate the effect of downregulation of eCBs. It can be assumed that hyper-function of the HPA axis from healthy to overt diabetes is due to the undermining inhibition of eCBs. However, the regulatory mechanism of eCBs targets on the HPA axis need to be further explored.

The Availability of Beneficial Insects-originated Materials on Women's Health following Menopause

Human health problems due to long life are becoming major issues in society, and in particular greater interest collected on women's health after menopause. Many substances can be introduced to women's health, however, materials from the substances have not shown all of the safety and efficacy properties that are not easily found. Currently, it is known about the effects of the disease on the female insect-derived material that is capable of overcoming this problem significantly. When using the insect-derived material through the results of several studies suggest that it is possible to solve a hormonal imbalance and nutritional imbalance in the elderly. Here, we'd like to try to dissertate about the new trends for women's health improvement using novel materials-derived from insects.

Activation of the hypothalamic-pituitary-adrenal axis in lithium-induced conditioned taste aversion learning

Intraperitoneal injections (ip) of lithium chloride at large doses induce c-Fos expression in the brain regions implicated in conditioned taste aversion (CTA) learning, and also activate the hypothalamic-pituitary-adrenal (HPA) axis and increase the plasma corticosterone levels in rats. A pharmacologic treatment blunting the lithium-induced c-Fos expression in the brain regions, but not the HPA axis activation, induced CTA formation. Synthetic glucocorticoids at conditioning, but not glucocorticoid antagonist, attenuated the lithium-induced CTA acquisition. The CTA acquisition by ip lithium was not affected by adrenalectomy regardless of basal corticosterone supplement, but the extinction was delayed in the absence of basal corticosterone. Glucocorticoids overloading delayed the extinction memory formation of lithium-induced CTA. ip lithium consistently induced the brain c-Fos expression, the HPA activation and CTA formation regardless of the circadian activation of the HPA axis. Intracerebroventricular (icv) injections of lithium at day time also increased the brain c-Fos expression, activated the HPA axis and induced CTA acquisition. However, icv lithium at night, when the HPA axis shows its circadian activation, did not induce CTA acquisition nor activate the HPA axis, although it increased the brain c-Fos expression. These results suggest that the circadian activation of the HPA axis may affect central, but not peripheral, effect of lithium in CTA learning in rats, and the HPA axis activation may be necessary for the central effect of lithium in CTA formation. Also, glucocorticoids may be required for a better extinction; however, increased glucocorticoids hinder both the acquisition and the extinction of lithium-induced CTA.

Effects of exercise on brain functions in diabetic animal models

Human life span has dramatically increased over several decades, and the quality of life has been considered to be equally important. However, diabetes mellitus (DM) characterized by problems related to insulin secretion and recognition has become a serious health problem in recent years that threatens human health by causing decline in brain functions and finally leading to neurodegenerative diseases. Exercise is recognized as an effective therapy for DM without medication administration. Exercise studies using experimental animals are a suitable option to overcome this drawback, and animal studies have improved continuously according to the needs of the experimenters. Since brain health is the most significant factor in human life, it is very important to assess brain functions according to the different exercise conditions using experimental animal models. Generally, there are two types of DM; insulin-dependent type 1 DM and an insulin-independent type 2 DM (T2DM); however, the author will mostly discuss brain functions in T2DM animal models in this review. Additionally, many physiopathologic alterations are caused in the brain by DM such as increased adiposity, inflammation, hormonal dysregulation, uncontrolled hyperphagia, insulin and leptin resistance, and dysregulation of neurotransmitters and declined neurogenesis in the hippocampus and we describe how exercise corrects these alterations in animal models. The results of changes in the brain environment differ according to voluntary, involuntary running exercises and resistance exercise, and gender in the animal studies. These factors have been mentioned in this review, and this review will be a good reference for studying how exercise can be used with therapy for treating DM.

The selective glucocorticoid receptor modulator CORT108297 restores faulty hippocampal parameters in Wobbler and corticosterone-treated mice

Mutant Wobbler mice are models for human amyotrophic lateral sclerosis (ALS). In addition to spinal cord degeneration, Wobbler mice show high levels of blood corticosterone, hyperactivity of the hypothalamic-pituitary-adrenal axis and abnormalities of the hippocampus. Hypersecretion of glucocorticoids increase hippocampus vulnerability, a process linked to an enriched content of glucocorticoid receptors (GR). Hence, we studied if a selective GR antagonist (CORT108297) with null affinity for other steroid receptors restored faulty hippocampus parameters of Wobbler mice. Three months old genotyped Wobbler mice received s.c. vehicle or CORT108297 during 4 days. We compared the response of doublecortin (DCX)+ neuroblasts in the subgranular layer of the dentate gyrus (DG), NeuN+ cells in the hilus of the DG, glial fibrillary acidic protein (GFAP)+ astrocytes and the phenotype of Iba1+ microglia in CORT108297-treated and vehicle-treated Wobblers. The number of DCX+ cells in Wobblers was lower than in control mice, whereas CORT108297 restored this parameter. After CORT108297 treatment, Wobblers showed diminished astrogliosis, and changed the phenotype of Iba1+ microglia from an activated to a quiescent form. These changes occurred without alterations in the hypercorticosteronemia or the number of NeuN+ cells of the Wobblers. In a separate experiment employing control NFR/NFR mice, treatment with corticosterone for 5 days reduced DCX+ neuroblasts and induced astrocyte hypertrophy, whereas treatment with CORT108297 antagonized these effects. Normalization of neuronal progenitors, astrogliosis and microglial phenotype by CORT108297 indicates the usefulness of this antagonist to normalize hippocampus parameters of Wobbler mice. Thus, CORT108297 opens new therapeutic options for the brain abnormalities of ALS patients and hyperadrenocorticisms.

Exercise prevents the increased anxiety-like behavior in lactational di-(2-ethylhexyl) phthalate-exposed female rats in late adolescence by improving the regulation of hypothalamus-pituitary-adrenal axis

Both the detrimental effects of early life adversity and the beneficial effects of exercise on the hypothalamic-pituitary-adrenal (HPA) axis have been reported. Early life exposure to di-(2-ethylhexyl)-phthalate (DEHP) may impair the development of endocrine system. In this study, we investigated the effects of lactational DEHP exposure on stress responses in late adolescent female rats and examined the protective role of treadmill running. Sprague-Dawley dams were fed with DEHP (10mg/kg per day) or vehicle during lactation. After weaning, the female offspring rats were trained to exercise on a treadmill for 5 weeks and then stressed by exploring on an elevated plus maze. The activities of HPA axis were evaluated by measuring the plasma levels of ACTH and corticosterone, the expressions of adrenal enzymes cholesterol side-chain cleavage enzyme (CYP11A1) and cytochrome P-450 11β-hydroxylase (CYP11B1), and the expression of hypothalamic glucocorticoid receptors (GR). The results demonstrate that DEHP-exposed rats exhibited enhanced anxiety-like behaviors. Increased hypothalamic GR and plasma ACTH levels, but decreased adrenal CYP11A1 and corticosterone levels, were observed in DEHP-exposed animals under stressed condition. Importantly, in DEHP-exposed animals, exercise during childhood-adolescence reduced anxiety-like behaviors by normalizing stress-induced alterations in ACTH level and adrenal CYP11A1 expression. The findings of this study suggest that treadmill running may provide beneficial effects on ameliorating the dysregulation of HPA axis in lactational DEHP-exposed adolescent female rats.

Increase of glucocorticoids is not required for the acquisition, but hinders the extinction, of lithium-induced conditioned taste aversion

Lithium chloride at doses sufficient to induce conditioned taste aversion (CTA) causes c-Fos expression in the paraventricular nucleus and increases the plasma level of corticosterone with activation of the hypothalamic-pituitary-adrenal axis. This study was conducted to define the role of glucocorticoid in the acquisition and extinction of lithium-induced CTA. In experiment 1, Sprague-Dawley rats received dexamethasone (2mg/kg) or RU486 (20mg/kg) immediately after 5% sucrose access, and then an intraperitoneal injection of isotonic lithium chloride (12ml/kg) was followed with 30min interval. Rats had either 1 or 7 days of recovery period before the daily sucrose drinking tests. In experiment 2, rats were conditioned with the sucrose-lithium pairing, and then received dexamethasone or vehicle at 30min before each drinking test. In experiment 3, adrenalectomized (ADX or ADX+B) rats were subjected to sucrose drinking tests after the sucrose-lithium pairing. Dexamethasone, but not RU486, pretreatment blunted the formation of lithium-induced CTA memory. Dexamethasone prior to each drinking test suppressed sucrose consumption and prolonged the extinction of lithium-induced CTA. Sucrose consumption was significantly suppressed not only in ADX+B rats but also in ADX rats during the first drinking session; however, a significant decrease was found only in ADX rats on the fourth drinking session. These results reveal that glucocorticoid is not a necessary component in the acquisition, but an important player in the extinction, of lithium-induced CTA, and suggest that a pulse increase of glucocorticoid may hinder the extinction memory formation of lithium-induced CTA.

Altered systemic cortisol metabolism in bipolar disorder and schizophrenia spectrum disorders

Dysfunction of the hypothalamic-pituitary-adrenal (HPA) axis is suggested as a pathophysiological factor in bipolar disorder and schizophrenia. Increased clearance of cortisol was recently indicated as a component in the HPA axis hyperdrive. The aim of the present study was to test the model of increased cortisol metabolism in a new replication sample separately and combined with a previously published sample of bipolar disorder and schizophrenia. Spot urine was sampled from 212 healthy controls (HC) and 221 patients with a schizophrenia spectrum disorder (SCZ, n = 115) and bipolar disorder (BD, n = 106). Of these, a subsample of 169 HC and 155 patients was included in a previous report. Urinary free cortisol, cortisone and their metabolites were measured, and the activities of 5α-reductase, 5β-reductase and 11β-HSD were estimated and analyzed for differences between groups. In the new sample, there was increased enzyme activity in SCZ for 5β-reductase (p = 0.024 vs HC; p = 0.027 vs BD) and 11β-HSD2 (p = 0.014 vs HC; p = 0.004 vs BD). In the combined sample, there was increased activity in SCZ for 5α-reductase (p < 0.001 vs HC; p = 0.020 vs BD), 5β-reductase (p < 0.001 vs HC; p = 0.045 vs BD) and 11β-HSD2 (p < 0.001 vs HC; p = 0.043 vs BD), and in BD for 5β-reductase (p = 0.002), 11β-HSD2 (p = 0.039) and 5α-reductase (trend, p = 0.084) (all vs HC). The findings confirm increased systemic cortisol metabolism in BD and SCZ. This is most consistent in SCZ, with BD taking an intermediate position. The design makes it impossible to determine the direction of the effect. However, the findings merit further study of cortisol metabolism as a possible component in the HPA axis dysfunction and pathophysiology of BD and SCZ.

Sequential alterations of glucocorticoid receptors in the hippocampus of STZ-treated type 1 diabetic rats

Type 1 diabetes is a common metabolic disorder accompanied by increased blood glucose levels along with glucocorticoid and cognitive deficits. The disease is also thought to be associated with environmental changes in brain and constantly induces oxidative stress in patients. Therefore, glucocorticoid-mediated negative feedback mechanisms involving the glucocorticoid receptor (GR) binding site are very important to understand the development of this disease. Many researchers have used streptozotocin (STZ)-treated diabetic animals to study changes in GR expression in the brain. However, few scientists have evaluated the hyperglycemic period following STZ exposure. In the present study, we found GR expression in the hippocampus varied based on the period after STZ administration for up to 4 weeks. We performed immunohistochemistry and Western blotting to validate the sequential alterations of GR expression in the hippocampus of STZ-treated type 1 diabetic rats. GR protein expression increased significantly until week 3 but decreased at week 4 following STZ administration. GR expression after 70 mg/kg STZ administration was highest at 3 weeks post-treatment and decreased thereafter. Although STZ-induced increase in GR expression in diabetic animals has been described, our data indicate that researchers should consider the sequential GR expression changes during the hyperglycemic period following STZ exposure.

Arginine vasopressin (AVP) expressional changes in the hypothalamic paraventricular and supraoptic nuclei of stroke-prone spontaneously hypertensive rats

Arginine vasopressin (AVP) is a neuropeptide with vasoconstrictive, antidiuretic, cardiovascular regulative and hepatic glycogenolysis effects, that also affects other behaviors including modulating learning. A number of studies on AVP regulation have been conducted in various metabolic diseases (disorders). In this study, the immunoreactivities of AVP in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) and mRNA expressions in the hypothalamus were investigated by immunohistochemistry and quantitative real-time PCR (RT-qPCR) in stroke-prone spontaneously hypertensive rats at different ages (i.e., at postnatal months [PM] 1, 8, and 12). Blood glucose levels in the PM 8 group were higher than in the other groups. However, cresyl violet positive neurons were detected in the PVN and SON of all animals, and numbers of cresyl violet positive neurons were similar in all aged groups. In addition, AVP immunoreactivity was detected in the PVN and SON of all age groups, and AVP immunoreactivity and mRNA expression levels were found to be increased in proportion to age by immunohistochemistry and RT-qPCR. These results suggest that the diabetic condition is temporally generated after hypertension has developed. Furthermore, our findings suggest that increased AVP expressions in the hypothalamic PVN and SON are associated with hypertension by age.

Modulation of pancreatic islets-stress axis by hypothalamic releasing hormones and 11beta-hydroxysteroid dehydrogenase

Corticotropin-releasing hormone (CRH) and growth hormone-releasing hormone (GHRH), primarily characterized as neuroregulators of the hypothalamic-pituitary-adrenal axis, directly influence tissue-specific receptor-systems for CRH and GHRH in the endocrine pancreas. Here, we demonstrate the expression of mRNA for CRH and CRH-receptor type 1 (CRHR1) and of protein for CRHR1 in rat and human pancreatic islets and rat insulinoma cells. Activation of CRHR1 and GHRH-receptor significantly increased cell proliferation and reduced cell apoptosis. CRH stimulated both cellular content and release of insulin in rat islet and insulinoma cells. At the ultrastructural level, CRHR1 stimulation revealed a more active metabolic state with enlarged mitochondria. Moreover, glucocorticoids that promote glucose production are balanced by both 11b-hydroxysteroid dehydrogenase (11β-HSD) isoforms; 11β-HSD-type-1 and 11β-HSD-type-2. We demonstrated expression of mRNA for 11β-HSD-1 and 11β-HSD-2 and protein for 11β-HSD-1 in rat and human pancreatic islets and insulinoma cells. Quantitative real-time PCR revealed that stimulation of CRHR1 and GHRH-receptor affects the metabolism of insulinoma cells by down-regulating 11β-HSD-1 and up-regulating 11β-HSD-2. The 11β-HSD enzyme activity was analyzed by measuring the production of cortisol from cortisone. Similarly, activation of CRHR1 resulted in reduced cortisol levels, indicating either decreased 11β-HSD-1 enzyme activity or increased 11β-HSD-2 enzyme activity; thus, activation of CRHR1 alters the glucocorticoid balance toward the inactive form. These data indicate that functional receptor systems for hypothalamic-releasing hormone agonists exist within the endocrine pancreas and influence synthesis of insulin and the pancreatic glucocorticoid shuttle. Agonists of CRHR1 and GHRH-receptor, therefore, may play an important role as novel therapeutic tools in the treatment of diabetes mellitus.