angiotensin-i and Diabetes-Mellitus--Type-2

The prevalence of Type 2 diabetes mellitus is predicted to increase dramatically over the coming years and the clinical implications and healthcare costs from this disease are overwhelming. In many cases, this pathological condition is linked to a cluster of metabolic disorders, such as obesity, systemic hypertension and dyslipidaemia, defined as the metabolic syndrome. Insulin resistance has been proposed as the key mediator of all of these features and contributes to the associated high cardiovascular morbidity and mortality. Although the molecular mechanisms behind insulin resistance are not completely understood, a negative cross-talk between AngII (angiotensin II) and the insulin signalling pathway has been the focus of great interest in the last decade. Indeed, substantial evidence has shown that anti-hypertensive drugs that block the RAS (renin-angiotensin system) may also act to prevent diabetes. Despite its long history, new components within the RAS continue to be discovered. Among them, Ang-(1-7) [angiotensin-(1-7)] has gained special attention as a counter-regulatory hormone opposing many of the AngII-related deleterious effects. Specifically, we and others have demonstrated that Ang-(1-7) improves the action of insulin and opposes the negative effect that AngII exerts at this level. In the present review, we provide evidence showing that insulin and Ang-(1-7) share a common intracellular signalling pathway. We also address the molecular mechanisms behind the beneficial effects of Ang-(1-7) on AngII-mediated insulin resistance. Finally, we discuss potential therapeutic approaches leading to modulation of the ACE2 (angiotensin-converting enzyme 2)/Ang-(1-7)/Mas receptor axis as a very attractive strategy in the therapy of the metabolic syndrome and diabetes-associated diseases.

Topics: Angiotensin I; Angiotensin II; Angiotensin II Type 1 Receptor Blockers; Angiotensin-Converting Enzyme 2; Angiotensin-Converting Enzyme Inhibitors; Animals; Diabetes Mellitus, Type 2; Humans; Hypoglycemic Agents; Insulin; Insulin Resistance; Peptide Fragments; Peptidyl-Dipeptidase A; Proto-Oncogene Mas; Proto-Oncogene Proteins; Receptors, G-Protein-Coupled; Renin-Angiotensin System; Signal Transduction

The canonical renin-angiotensin system (RAS) involves the initial action of renin to cleave angiotensinogen to angiotensin I (ANG I), which is then converted to ANG II by the angiotensin converting enzyme (ACE). ANG II plays a critical role in numerous physiological functions, and RAS overactivity underlies many conditions of cardiovascular dysregulation. In addition, ANG II, by acting on both endothelial and myocellular AT1 receptors, can induce insulin resistance by increasing cellular oxidative stress, leading to impaired insulin signaling and insulin-stimulated glucose transport activity. This insulin resistance associated with RAS overactivity, when coupled with progressive ß-cell dysfunction, eventually leads to the development of type 2 diabetes. Interventions that target RAS overactivity, including ACE inhibitors, ANG II receptor blockers, and, most recently, renin inhibitors, are effective both in reducing hypertension and in improving whole-body and skeletal muscle insulin action, due at least in part to enhanced Akt-dependent insulin signaling and insulin-dependent glucose transport activity. ANG-(1-7), which is produced from ANG II by the action of ACE2 and acts via Mas receptors, can counterbalance the deleterious actions of the ACE/ANG II/AT1 receptor axis on the insulin-dependent glucose transport system in skeletal muscle. This beneficial effect of the ACE2/ANG-(1-7)/Mas receptor axis appears to depend on the activation of Akt. Collectively, these findings underscore the importance of RAS overactivity in the multifactorial etiology of insulin resistance in skeletal muscle, and provide support for interventions that target the RAS to ameliorate both cardiovascular dysfunctions and insulin resistance in skeletal muscle tissue.

Topics: Angiotensin I; Angiotensin II; Angiotensin Receptor Antagonists; Angiotensin-Converting Enzyme 2; Angiotensin-Converting Enzyme Inhibitors; Animals; Biological Transport, Active; Diabetes Mellitus, Type 2; Glucose; Humans; Insulin Resistance; Insulin-Secreting Cells; Muscle, Skeletal; Peptidyl-Dipeptidase A; Receptor, Angiotensin, Type 1; Renin-Angiotensin System

Angiotensin type 1 (AT1) receptor blockers (ARBs) are used to treat hypertension and related end-organ damage. ARBs have been recognised as regulators of glucose- and lipid metabolism. Clinical trials demonstrated that AT1 receptor antagonism lowers the risk for type 2 diabetes compared with other antihypertensive therapies. Blockade of AT1 receptors reduces cardiovascular morbidity and mortality in diabetic subpopulations. The mechanisms of the insulin-sensitizing/anti-diabetic effect are not fully understood, and may involve AT1 receptor-dependent pathways and 'pleiotropic' actions of ARBs including activation of insulin-sensitising PPARgamma.. In clinical practice questions about AT1 receptor blockade in diabetes have to be answered. Firstly, is selective AT1-receptor blockade superior to ACE inhibition in preventing diabetes and reducing cardiovascular end points in diabetic patients? Secondly, is an ARB with PPARgamma-activating properties superior to one without this action?. The Ongoing Telmisartan Alone and in Combination with Ramipril Global End point Trial (ONTARGET) has provided information to answer these questions, and is discussed.

Topics: Angiotensin I; Angiotensin Receptor Antagonists; Diabetes Mellitus, Type 2; Glucose; Humans; Insulin; Insulin Resistance; PPAR gamma; Receptors, Angiotensin

Activation of the renin-angiotensin system has a pivotal role in the pathogenesis of diabetic complications. However, recent evidence suggests that it may also contribute to the development of diabetes itself. In the endocrine pancreas, all the components of an active renin-angiotensin system are present, which modulate a range of activities including local blood flow, hormone release and prostaglandin synthesis. In both types 1 and 2 diabetes, there is an up-regulation of its expression and activity in the endocrine pancreas. Whether these changes have a direct pathogenetic role or reflect a response to local stress or tissue injury remains to be established. Angiotensin-mediated increases in oxidative stress, inflammation and free fatty acids levels potentially contribute to beta-cell dysfunction in diabetes. In addition, activation of the renin-angiotensin system appears to potentiate the action of other pathogenic pathways including glucotoxicity, lipotoxicity and advanced glycation. In experimental models of type 2 diabetes, blockade of the renin-angiotensin system with angiotensin converting enzyme inhibitors or angiotensin receptor antagonists results in the improvement of islet structure and function. Moreover, the incidence of de novo diabetes appears to be significantly reduced by blockade of the renin-angiotensin system in clinical studies. At least two large controlled trials are currently underway to study the role of renin-angiotensin system in the development of diabetes. It is hoped that these studies will demonstrate the true potential of the blockade of the renin-angiotensin system for the prevention of diabetes.

Topics: Angiotensin I; Angiotensin II; Angiotensinogen; Animals; Diabetes Mellitus; Diabetes Mellitus, Type 1; Diabetes Mellitus, Type 2; Fibrosis; Humans; Hyperglycemia; Hypoglycemia; Islets of Langerhans; Pancreas; Peptidyl-Dipeptidase A; PPAR gamma; Receptors, Angiotensin; Renin; Renin-Angiotensin System

This is the second part in a series of papers dealing with various aspects of clinical pharmacology of the first AT1-receptor antagonist losartan and its therapeutic use in hypertension, diabetic nephropathy, chronic heart failure, and acute phase of myocardial infarction. This part contains review of literature data concerning the use of losartan for the treatment of hypertension and diabetic nephropathy including results of two major randomized trials which for the first time demonstrated ability of losartan to improve long term prognosis in patients with hypertension and diabetic nephropathy.

Topics: Angiotensin I; Angiotensin Receptor Antagonists; Antihypertensive Agents; Benzimidazoles; Biphenyl Compounds; Blood Pressure; Diabetes Mellitus, Type 2; Diabetic Nephropathies; Diastole; Diuretics; Drug Therapy, Combination; Humans; Hydrochlorothiazide; Hypertension; Irbesartan; Losartan; Meta-Analysis as Topic; Placebos; Prognosis; Randomized Controlled Trials as Topic; Sodium Chloride Symporter Inhibitors; Systole; Tetrazoles; Time Factors; Treatment Outcome; Valine; Valsartan

Topics: Aged; Angiotensin I; Angiotensin II; Angiotensin-Converting Enzyme Inhibitors; Biphenyl Compounds; Diabetes Mellitus, Type 1; Diabetes Mellitus, Type 2; Diabetic Nephropathies; Female; Humans; Irbesartan; Losartan; Male; Middle Aged; Primary Prevention; Prognosis; Randomized Controlled Trials as Topic; Risk Assessment; Sensitivity and Specificity; Tetrazoles; Treatment Outcome

In chronic heart failure there is gradual reactivation of vascular tissue angiotensin I (AI) to angiotensin II (AII) conversion over time in patients taking chronic ACE inhibitor therapy. However, it remains unknown whether the same overall phenomenon occurs in other patients taking chronic ACE inhibitor therapy, such as patients with type 2 diabetes mellitus.. We studied 30 patients with type 2 diabetes mellitus (mean age 43.5 +/- 10.8 years), all of whom received lisinopril (20 mg/day) as part of their normal treatment. Over the course of the 18 month study, we made measurements at 0, 9 and 18 months. These measurements included plasma values for components of the renin-angiotensin-aldosterone system. In addition, we infused AI and AII into the brachial arteries of patients to assess vascular tissue AI to AII conversion.. There were no significant changes in plasma renin activity, ACE, AI, AII or aldosterone during the study. In contrast, vascular AI to AII conversion was significantly (p = 0.01) greater at 18 months than at 0 months. There was no change over time in the response to infused AII.. We have shown in vivo that vascular tissue AI to AII conversion gradually increases over time in patients with type 2 diabetes being treated with lisinopril. Further studies are required to determine whether this reactivation detracts from the cardioprotective effects of chronic ACE inhibitor therapy in diabetic patients, and if so, how best to overcome it.

Topics: Adult; Aged; Aldosterone; Angiotensin I; Angiotensin II; Angiotensin-Converting Enzyme Inhibitors; Blood Flow Velocity; Diabetes Mellitus, Type 2; Diabetic Angiopathies; Female; Humans; Hypertension; Kinetics; Lisinopril; Male; Middle Aged

We have demonstrated previously that inhibition of angiotensin-converting enzyme (ACE) with enalapril and angiotensin II blockade with losartan improve acetylcholine-dependent endothelial function in resistance vessels of patients with Type II diabetes. It was therefore of interest to examine the effect of losartan on conduit vessel function in this group. The influence of losartan (50 mg daily for 4 weeks) on endothelium-dependent and -independent vasodilator function was determined in 12 subjects with Type II diabetes using a randomized, double-blind, placebo-controlled crossover protocol. Conduit vessel endothelial function was assessed using high-resolution ultrasound and the brachial artery response to reactive hyperaemia (flow-mediated dilation; FMD); glyceryl trinitrate (GTN) was used as a non-endothelium-dependent dilator. Losartan administration significantly increased the FMD response from 5.2+/-0.7% (mean+/-S.E.M.) to 7.4+/-0.6% of vessel diameter (P<0.05; paired t-test). There was no effect of losartan on the endothelium-independent responses to GTN (17.8+/-1.8% to 17.6+/-1.2%). Consistent with our previous findings in resistance vessels, administration of 50 mg of losartan daily improves NO-mediated dilation in the conduit vessels of subjects with Type II diabetes. Together with the findings that both ACE inhibition and angiotensin II blockade improve resistance vessel function in this group, it is likely that at least some of the beneficial effect is mediated through the angiotensin II/type I receptor pathway. A type I receptor antagonist seems a reasonable alternative to an ACE inhibitor to maintain conduit vessel endothelial function in Type II diabetic subjects.

Topics: Angiotensin I; Angiotensin Receptor Antagonists; Cross-Over Studies; Diabetes Mellitus, Type 2; Double-Blind Method; Endothelium, Vascular; Female; Humans; Losartan; Male; Middle Aged; Vasodilation

This study explores the role of inducible nitric oxide synthase (iNOS) in the pathogenesis of diabetes mellitus-induced erectile dysfunction (DMED) and the effect of angiotensin 1-7 (Ang- [1-7]) on NOS levels. A type 2 diabetes mellitus (DM) rat model was established. Erectile function was assessed by measuring intracavernous pressure and mean arterial pressure after electrical stimulation. The expression of iNOS, endothelial NOS (eNOS), eNOS phosphorylated at Ser 1177 (p-eNOS [Ser 1177]), and AKT/p-AKT in corpus cavernosum smooth muscle cells (CCSMCs) was measured by Western blotting and immunofluorescence. The plasma levels of NO, SOD, malondialdehyde, and peroxynitrite were calculated. Intracellular calcium content was determined by flow cytometry. DMED rats exhibited decreased erectile function and severe oxidative stress. Ang-(1-7) treatment improved erectile response and suppressed oxidative stress by upregulating p-eNOS/eNOS and downregulating iNOS levels. Silencing iNOS in CCSMCs decreased oxidative stress and intracellular calcium levels induced by high glucose. In turn, iNOS overexpression increased oxidative stress and intracellular calcium level. Treatment with the MAS receptor antagonist A779 and the Akt antagonist LY294002 reversed the effects of Ang-(1-7) on iNOS. Ang-(1-7) improved DMED through the MAS/AKT signaling pathway.

Topics: Angiotensin I; Animals; Calcium; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 2; Erectile Dysfunction; Humans; Male; Nitric Oxide; Nitric Oxide Synthase; Nitric Oxide Synthase Type II; Nitric Oxide Synthase Type III; Peptide Fragments; Proto-Oncogene Proteins c-akt; Rats

Increased angiotensin II (Ang II) signaling contributes to insulin resistance and liver steatosis. In addition to ameliorating hypertension, angiotensin receptor blockers (ARBs) improve lipid metabolism and hepatic steatosis, which are impaired with metabolic syndrome (MetS). Chronic blockade of the Ang II receptor type 1 (AT1) increases plasma angiotensin 1-7 (Ang 1-7), which mediates mechanisms counterregulatory to AT1 signaling. Elevated plasma Ang 1-7 is associated with decreased plasma triacylglycerol (TAG), cholesterol, glucose, and insulin; however, the benefits of RAS modulation to prevent non-alcoholic fatty liver disease (NAFLD) are not fully investigated. To better address the relationships among chronic ARB treatment, plasma Ang 1-7, and hepatic steatosis, three groups of 10-week-old-rats were studied: (1) untreated lean Long Evans Tokushima Otsuka (LETO), (2) untreated Otsuka Long Evans Tokushima Fatty (OLETF), and (3) OLETF + ARB (ARB; 10 mg olmesartan/kg/d × 6 weeks). Following overnight fasting, rats underwent an acute glucose load to better understand the dynamic metabolic responses during hepatic steatosis and early MetS. Tissues were collected at baseline (pre-load; T0) and 1 and 2 h post-glucose load. AT1 blockade increased plasma Ang 1-7 and decreased liver lipids, which was associated with decreased fatty acid transporter 5 (FATP5) and fatty acid synthase (FASN) expression. AT1 blockade decreased liver glucose and increased glucokinase (GCK) expression. These results demonstrate that during MetS, overactivation of AT1 promotes hepatic lipid deposition that is stimulated by an acute glucose load and lipogenesis genes, suggesting that the chronic hyperglycemia associated with MetS contributes to fatty liver pathologies via an AT1-mediated mechanism.

Topics: Angiotensin I; Angiotensin Receptor Antagonists; Angiotensin-Converting Enzyme Inhibitors; Animals; Diabetes Mellitus, Type 2; Fatty Liver; Gene Expression; Glucose; Insulin; Lipogenesis; Liver; Metabolic Syndrome; Obesity; Peptide Fragments; Rats; Rats, Inbred OLETF; Receptor, Angiotensin, Type 1

To study the changes and effects of angiotensin-converting enzyme 2 (ACE2)/angiotensin 1-7 (Ang1-7) and ACE/AngII in people with different glucose metabolisms and to explore the possible mechanisms underlying the severity of COVID-19 infection in diabetic patients.. A total of 88 patients with type 2 diabetes, 72 patients with prediabetes (impaired fasting glucose, 30 patients; impaired glucose regulation, 42 patients), and 50 controls were selected. Changes and correlations of ACE2, Ang1-7 and other indicators were detected among the three groups. Patients were divided into four groups according to the course of diabetes: <1 year, 1-5 years, 5-10 years, and >10 years. ACE2 and Ang1-7 levels were compared and analyzed.. ACE2 and Ang1-7 increased with the severity of diabetes (P0 < .05 or P < .01). The levels of ACE2 and Ang1-7 in the longer course group were lower than those in the shorter course group, whereas the levels of ACE, Ang II, and interleukin-6 (IL-6) gradually increased (P < .05). Pearson correlation analysis showed that ACE2 was positively correlated with IL-6, FBG, and 2hPBG levels in the prediabetes group. In the diabetic group, ACE2 was positively correlated with Ang1-7 and negatively correlated with ACE, AngII, IL-6, and C-reactive protein levels. Multiple linear regression analysis showed that IL-6 and ACE were the main factors influencing ACE2 in the diabetic group.. ACE2/Ang1-7 and ACE/AngII systems are activated, and inflammatory cytokine release increases in prediabetes. With the prolongation of the disease course, the effect of ACE2/Ang1-7 decreased gradually, while the effect of ACE/AngII increased significantly. Dysfunctions of ACE2/Ang1-7 may be one of the important mechanisms underlying the severity of COVID-19 infection in patients with diabetes.

Topics: Angiotensin I; Angiotensin II; Angiotensin-Converting Enzyme 2; C-Reactive Protein; COVID-19; Diabetes Mellitus, Type 2; Glucose; Humans; Interleukin-6; Peptide Fragments; Prediabetic State

We have previously reported that the spinal angiotensin (Ang) system is involved in the modulation of streptozotocin (STZ)-induced diabetic neuropathic pain in mice. An important drawback of this model however is the fact that the neuropathic pain is independent of hyperglycemia and produced by the direct stimulation of peripheral nerves. Here, using the leptin deficient ob/ob mouse as a type 2 diabetic model, we examined whether the spinal Ang system was involved in naturally occuring diabetic neuropathic pain. Blood glucose levels were increased in ob/ob mice at 5-15 weeks of age. Following the hyperglycemia, persistent tactile and thermal hyperalgesia were observed at 11-14 and 9-15 weeks of age, respectively, which was ameliorated by insulin treatment. At 12 weeks of age, the expression of Ang-converting enzyme (ACE) 2 in the spinal plasma membrane fraction was decreased in ob/ob mice. Spinal ACE2 was expressed in neurons and microglia but the number of NeuN-positive neurons was decreased in ob/ob mice. In addition, the intrathecal administration of Ang (1-7) and SB203580, a p38 MAPK inhibitor, attenuated hyperalgesia in ob/ob mice. The phosphorylation of spinal p38 MAPK was also attenuated by Ang (1-7) in ob/ob mice. These inhibitory effects of Ang (1-7) were prevented by A779, a Mas receptor antagonist. In conclusion, we revealed that the Ang (1-7)-generating system is downregulated in ob/ob mice and is accompanied by a loss of ACE2-positive neurons. Furthermore, Ang (1-7) decreased the diabetic neuropathic pain through inhibition of p38 MAPK phosphorylation via spinal Mas receptors.

Topics: Angiotensin I; Angiotensin-Converting Enzyme 2; Animals; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 2; Down-Regulation; Male; Mice; Mice, Knockout; Mice, Obese; Mice, Transgenic; Neuralgia; p38 Mitogen-Activated Protein Kinases; Peptide Fragments; Peptidyl-Dipeptidase A; Spinal Cord

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the third coronavirus leading to a global health outbreak. Despite the high mortality rates from SARS-CoV-1 and Middle-East respiratory syndrome (MERS)-CoV infections, which both sparked the interest of the scientific community, the underlying physiopathology of the SARS-CoV-2 infection, remains partially unclear. SARS-CoV-2 shares similar features with SARS-CoV-1, notably the use of the angiotensin conversion enzyme 2 (ACE2) as a receptor to enter the host cells. However, some features of the SARS-CoV-2 pandemic are unique. In this work, we focus on the association between obesity, metabolic syndrome, and type 2 diabetes on the one hand, and the severity of COVID-19 infection on the other, as it seems greater in these patients. We discuss how adipocyte dysfunction leads to a specific immune environment that predisposes obese patients to respiratory failure during COVID-19. We also hypothesize that an ACE2-cleaved protein, angiotensin 1-7, has a beneficial action on immune deregulation and that its low expression during the SARS-CoV-2 infection could explain the severity of infection. This introduces angiotensin 1-7 as a potential candidate of interest in therapeutic research on CoV infections.

Topics: Adipokines; Angiotensin I; Angiotensin-Converting Enzyme 2; Betacoronavirus; Coronavirus Infections; COVID-19; Diabetes Mellitus, Type 2; Humans; Metabolic Syndrome; Obesity; Pandemics; Peptide Fragments; Peptidyl-Dipeptidase A; Pneumonia, Viral; SARS-CoV-2; Severe Acute Respiratory Syndrome

Native angiotensin-(1-7) exerts many therapeutic effects. However, it is rapidly degraded by ACE and other peptidases. This drawback is largely eliminated for lanthionine-stabilized angiotensin-(1-7), termed cAng-(1-7), which is fully resistant to ACE and has strongly increased resistance to other peptidases. Goal of the present study was to test whether cAng-(1-7) has therapeutic activity in diabetes mouse models: in a multiple low dose streptozotocin-induced model of type I diabetes and / or in a db/db model of type II diabetes. In the type I diabetes model cAng-(1-7) caused in an increase in the insulin level of 133% in week 4 (p < 0.001) compared to vehicle, and in the type II diabetes model an increase of 55% of the insulin level in week 8 (p < 0.05) compared to vehicle. cAng-(1-7) reduced blood glucose levels in the type I model by 37% at day 22 (p < 0.001) and in the type II diabetes model by 17% at day 63 of treatment (p < 0.001) and in an oral glucose tolerance test in a type II diabetes model, by 17% at week 4 (p < 0.01). cAng-(1-7) also caused a reduction of glycated hemoglobin levels in the type II diabetes model of 21% in week 6 (p < 0,001). These data are consistent with therapeutic potential of cAng-(1-7) in type I and II diabetes.

Topics: Alanine; Angiotensin I; Animals; Blood Glucose; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 1; Diabetes Mellitus, Type 2; Female; Insulin; Mice; Mice, Inbred C57BL; Peptide Fragments; Streptozocin; Sulfides; Treatment Outcome

The Renin-Angiotensin System (RAS) possesses a counter-regulatory axis composed of angiotensin converting enzyme (ACE)2, angiotensin-(1-7) [Ang-(1-7)] and the Mas receptor, which opposes many AT1-receptor-mediated effects of ligand angiotensin II. Ang-(1-7), as a ligand of the Mas receptor, has inhibitory effects on renal inflammation and fibrosis in experimental diabetes. However, Ang-(1-7) has a short half-life in plasma, which may render it unsuitable for use in clinics. Here, we investigated the effects of the lanthionine-stabilized Ang-(1-7), cyclic (c)Ang-(1-7), a lanthipeptide that is more peptidase-resistant than the linear peptide, in BTBR ob/ob mice with type 2 diabetic nephropathy. BTBR ob/ob mice received vehicle, cAng-(1-7), or the ACE inhibitor lisinopril. The treatment started at ten weeks of age, when the animals had already developed albuminuria, and ended at 19-20 weeks of age. cAng-(1-7) limited albuminuria progression, and limited podocyte dysfunction similarly to lisinopril. cAng-(1-7), unlike lisinopril, reduced glomerular fibrosis and inflammation, and counteracted glomerular capillary rarefaction. Furthermore, when cAng-(1-7) was combined with lisinopril, a superior antiproteinuric effect than with lisinopril alone was found, in association with better preservation of podocyte proteins and amelioration of capillary density. Thus, adding cAng-(1-7) to ACE-inhibitor therapy could benefit those diabetic patients who do not respond completely to ACE-inhibitor therapy.

Topics: Alanine; Angiotensin I; Angiotensin-Converting Enzyme Inhibitors; Animals; Diabetes Mellitus, Type 2; Diabetic Nephropathies; Disease Models, Animal; Drug Therapy, Combination; Half-Life; Humans; Kidney Glomerulus; Lisinopril; Male; Mice; Mice, Transgenic; Microscopy, Electron, Transmission; Peptide Fragments; Peptides, Cyclic; Proteinuria; Sulfides

Congestive heart failure is one of the most prevalent and deadly complications of type 2 diabetes that is frequently associated with pulmonary dysfunction. Among many factors that contribute to development and progression of diabetic complications is angiotensin II (Ang2). Activation of pathological arm of renin-angiotensin system results in increased levels of Ang2 and signaling through angiotensin type 1 receptor. This pathway is well recognized for its role in induction of oxidative stress (OS), inflammation, hypertrophy and fibrosis. Angiotensin (1-7) [A(1-7)], through activation of Mas receptor, opposes the actions of Ang2 which can result in the amelioration of diabetic complications; enhancing the overall welfare of diabetic patients. In this study, 8 week-old db/db mice were administered A(1-7) daily via subcutaneous injections. After 16 weeks of treatment, echocardiographic assessment of heart function demonstrated significant improvement in cardiac output, stroke volume and shortening fraction in diabetic animals. A(1-7) also prevented cardiomyocyte hypertrophy, apoptosis, lipid accumulation, and decreased diabetes-induced fibrosis and OS in the heart tissue. Treatment with A(1-7) reduced levels of circulating proinflammatory cytokines that contribute to the low grade inflammation observed in diabetes. In addition, lung pathologies associated with type 2 diabetes, including fibrosis and congestion, were decreased with treatment. OS and macrophage infiltration were also reduced in the lungs after treatment with A(1-7). Long-term administration of A(1-7) to db/db mice is effective in improving heart and lung function in db/db mice. Treatment prevented pathological remodeling of the tissues and reduced OS, fibrosis and inflammation.

Topics: Angiotensin I; Animals; Anti-Inflammatory Agents; Antioxidants; Apoptosis; Cardiotonic Agents; Cytokines; Diabetes Mellitus, Type 2; Disease Models, Animal; Fibrosis; Heart; Hypoglycemic Agents; Lipid Metabolism; Lung; Male; Mice; Myocardium; Oxidative Stress; Peptide Fragments

Angiotensin-converting enzyme 2 (ACE2)-angiotensin (1-7) [Ang (1-7)]-Mas constitutes the vasoprotective axis and is demonstrated to antagonize the vascular pathophysiological effects of the classical renin-angiotensin system. We sought to study the hypothesis that upregulation of ACE2-Ang (1-7) signaling protects endothelial function through reducing oxidative stress that would result in beneficial outcome in diabetes.. Ex vivo treatment with Ang (1-7) enhanced endothelium-dependent relaxation (EDR) in renal arteries from diabetic patients. Both Ang (1-7) infusion via osmotic pump (500 ng/kg/min) for 2 weeks and exogenous ACE2 overexpression mediated by adenoviral ACE2 via tail vein injection (10(9) pfu/mouse) rescued the impaired EDR and flow-mediated dilatation (FMD) in db/db mice. Diminazene aceturate treatment (15 mg/kg/day) activated ACE2, increased the circulating Ang (1-7) level, and augmented EDR and FMD in db/db mouse arteries. In addition, activation of the ACE2-Ang (1-7) axis reduced reactive oxygen species (ROS) overproduction determined by dihydroethidium staining, CM-H2DCFDA fluorescence imaging, and chemiluminescence assay in db/db mouse aortas and also in high-glucose-treated endothelial cells. Pharmacological benefits of ACE2-Ang (1-7) upregulation on endothelial function were confirmed in ACE2 knockout (ACE2 KO) mice both ex vivo and in vitro.. We elucidate that the ACE2-Ang (1-7)-Mas axis serves as an important signal pathway in endothelial cell protection in diabetic mice, especially in diabetic human arteries.. Endogenous ACE2-Ang (1-7) activation or ACE2 overexpression preserves endothelial function in diabetic mice through increasing nitric oxide bioavailability and inhibiting oxidative stress, suggesting the therapeutic potential of ACE2-Ang(1-7) axis activation against diabetic vasculopathy. Antioxid.

Topics: Acetylcholine; Aged; Angiotensin I; Angiotensin-Converting Enzyme 2; Animals; Aorta; Cells, Cultured; Diabetes Mellitus, Type 2; Diminazene; Female; Human Umbilical Vein Endothelial Cells; Humans; Male; Mice, Inbred C57BL; Middle Aged; Oxidative Stress; Peptide Fragments; Peptidyl-Dipeptidase A; Reactive Oxygen Species; Renal Artery; Up-Regulation; Vasodilator Agents

Diabetes mellitus type 2 (DM2) is a disease with increasing importance in modern societies and insufficient treatment options. Pharmacological stimulation of insulin signaling, which is blunted in DM2, is a promising approach to treat this disease. It has been shown that activation of the angiotensin (Ang)-(1-7)/Mas axis of the renin-angiotensin system leads to an improved glucose uptake. In this study, we intended to evaluate, whether this effect could be exploited therapeutically. We first confirmed that Ang-(1-7) improves insulin signaling and glucose uptake in vitro in cultured cardiomyocytes. We then evaluated the therapeutic effect of a newly developed hydro-xypropyl-β-cyclodextrin-based Ang-(1-7) nano-formulation in a novel transgenic rat model of inducible insulin resistance and DM2. The chronic administration of this compound prevented the marked elevation in blood glucose levels in these rats at a dose of 30 μg/kg, reversed the established hyperglycemic state at a dose of 100 μg/kg, and resulted in improved insulin sensitivity, reduced plasma insulin and decreased diabetic nephropathy. In conclusion, an oral Ang-(1-7) formulation reverses hyperglycemia and its consequences in an animal model of DM2 and represents a novel therapeutic option for the treatment of DM2 and other cardio-metabolic diseases.. A novel rat model with inducible diabetes can be used to evaluate new therapies. Angiotensin-(1-7) is effective in an oral formulation packaged in cyclodextrine. Angiotensin-(1-7) is a promising antidiabetic drug.

Topics: Administration, Oral; Angiotensin I; Animals; Animals, Newborn; Deoxyglucose; Diabetes Mellitus, Type 2; Hyperglycemia; Hypoglycemic Agents; Insulin; Male; Myocytes, Cardiac; Peptide Fragments; Phosphorylation; Proto-Oncogene Proteins c-akt; Rats; Rats, Sprague-Dawley; Signal Transduction

Pancreatic microcirculation plays a pivotal role in the physiological function and survival of β-cells. Ang(1- 7) is a novel component of the renin angiotensin system (RAS) that has beneficial effects on microcirculation. In the present study, we investigated the effects of systemic Ang(1-7) administration (with or without its receptor Mas antagonist A- 779) on pancreatic microcirculation and β-cell function.. These effects were studied in vivo using a rat model of Type 2 diabetes (T2DM). Pancreatic microcirculation and islet microvessel density were measured; and β-cell function, insulin content, and the apoptosis of islet cells were assessed, respectively. Additionally, we evaluated endothelial nitric oxide synthase (eNOS) expression and nitric oxide (NO) concentration in islets.. After Ang(1-7) intervention, pancreatic microcirculation and intra-islet microvessel density were significantly improved (p<0.05), and more importantly, first-phase insulin secretion of β-cells as well as relative insulin content in islets were increased, and the amount of apoptotic islet cells was decreased (p<0.05). And eNOS expression and NO release were up-regulated in pancreatic islets by Ang(1-7) administration (p<0.05). These positive effects of Ang(1-7) were prevented by the addition of A-779 (p<0.05).. Our findings suggest that systemic Ang(1-7) treatment could attenuate β-cell dysfunction and ameliorate islet cell apoptosis in T2DM rats by improving pancreatic microcirculation, perhaps through the mechanism of endothelial vasodilation.

Topics: Angiotensin I; Angiotensin II; Animals; Apoptosis; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 2; Diet, High-Fat; Disease Models, Animal; Insulin; Insulin Secretion; Islets of Langerhans; Male; Microcirculation; Nitric Oxide; Nitric Oxide Synthase Type III; Pancreas; Peptide Fragments; Rats; Rats, Wistar

We recently found that overexpression of angiotensin (Ang)-converting enzyme 2, which metabolizes Ang-II to Ang-(1-7) and Ang-I to Ang-(1-9), may prevent diabetes-induced left ventricular remodeling and dysfunction in rats. Our objective was to evaluate the association of plasma Ang-(1-7) level and left ventricular function in patients with type 2 diabetes mellitus.. We measured the left ventricular ejection fraction (EF), ratio of early to late left ventricular filling velocity (E/A) and ratio of early diastolic mitral inflow to annular velocity (E/Ea) by ultrasonography in 110 patients with type 2 diabetes mellitus for more than 5 years. Anthropometric and fasting blood values were obtained from medical records. The plasma Ang-(1-7) level in patients with a poor EF (<50%) was significantly lower than that in patients with EF ≥50%; the level in patients with E/A <1 was significantly lower than that in patients with E/A ≥1; and the level in patients with E/Ea >15 was significantly lower than that in patients with E/Ea ≤15. Ang-(1-7) level was negatively correlated with E/Ea and Log-N-terminal pro-B-type natriuretic peptide and positively with EF and E/A. Stepwise multiple regression analysis revealed that Ang-(1-7), hemoglobin A1c and Ang-II levels as well as duration of diabetes predicted EF; Ang-(1-7) level, fasting blood glucose, low-density lipoprotein cholesterol level and duration of diabetes predicted E/A; and Ang-(1-7) and hemoglobin A1c levels predicted E/Ea.. Plasma Ang-(1-7) level is independently associated with left ventricular function in patients with type 2 diabetes mellitus and may be a biomarker for assessing cardiac function in such patients.

Topics: Aged; Angiotensin I; Diabetes Mellitus, Type 2; Female; Humans; Male; Peptide Fragments; Stroke Volume; Ventricular Dysfunction, Left

ANG-(1-7) is associated with vasodilation and nitric oxide synthase stimulation. However, the role of ANG-(1-7) in type 2 diabetes mellitus is unknown. In this study, we examined the hypothesis that ANG-(1-7) attenuates ANG II-induced reactive oxygen species stress (ROS)-mediated injury in type 2 diabetic nephropathy of KK-A(y)/Ta mice. KK-A(y)/Ta mice were divided into four groups: 1) a control group; 2) ANG II infusion group; 3) ANG II+ANG-(1-7) coinfusion group; and 4) ANG II+ANG-(1-7)+d-Ala(7)-ANG-(1-7) (A779) coinfusion group. In addition, primary mesangial cells were cultured and then stimulated with 25 mM glucose with or without ANG II, ANG-(1-7), and A779. The ANG II+ANG-(1-7) coinfusion group showed a lower urinary albumin/creatinine ratio increase than the ANG II group. ANG-(1-7) attenuated ANG II-mediated NAD(P)H oxidase activation and ROS production in diabetic glomeruli and mesangial cells. ANG II-induced NF-κB and MAPK signaling activation was also attenuated by ANG-(1-7) in the mesangial cells. These findings were related to improved mesangial expansion and to fibronectin and transforming growth factor-β1 production in response to ANG II and suggest that ANG-(1-7) may attenuate ANG II-stimulated ROS-mediated injury in type 2 diabetic nephropathy. The ACE2-ANG-(1-7)-Mas receptor axis should be investigated as a novel target for treatment of type 2 diabetic nephropathy.

Topics: Angiotensin I; Angiotensin II; Animals; Blood Pressure; Blotting, Western; Body Weight; Cells, Cultured; Diabetes Mellitus, Type 2; Diabetic Nephropathies; Immunohistochemistry; Mesangial Cells; Mice; NADPH Oxidases; Peptide Fragments; Reactive Oxygen Species; Reverse Transcriptase Polymerase Chain Reaction; Statistics, Nonparametric

Combination therapy of angiotensin-converting enzyme (ACE) inhibition and AT(1) receptor blockade has been shown to provide greater renoprotection than ACE inhibitor alone in human diabetic nephropathy, suggesting that ACE-independent pathways for ANG II formation are of major significance in disease progression. Studies were performed to determine the magnitude of intrarenal ACE-independent formation of ANG II in type II diabetes. Although renal cortical ACE protein activity [2.1 +/- 0.8 vs. 9.2 +/- 2.1 arbitrary fluorescence units (AFU) x mg(-1) x min(-1)] and intensity of immunohistochemical staining were significantly reduced and ACE2 protein activity (16.7 +/- 3.2 vs. 7.2 +/- 2.4 AFU x mg(-1) x min(-1)) and intensity elevated, kidney ANG I (113 +/- 24 vs. 110 +/- 45 fmol/g) and ANG II (1,017 +/- 165 vs. 788 +/- 99 fmol/g) levels were not different between diabetic and control mice. Afferent arteriole vasoconstriction due to conversion of ANG I to ANG II was similar in magnitude in kidneys of diabetic (-28 +/- 3% at 1 microM) and control (-23 +/- 3% at 1 microM) mice; a response completely inhibited by AT(1) receptor blockade. In control kidneys, afferent arteriole vasoconstriction produced by ANG I was significantly attenuated by ACE inhibition, but not by serine protease inhibition. In contrast, afferent arteriole vasoconstriction produced by intrarenal conversion of ANG I to ANG II was significantly attenuated by serine protease inhibition, but not by ACE inhibition in diabetic kidneys. In conclusion, there is a switch from ACE-dependent to serine protease-dependent ANG II formation in the type II diabetic kidney. Pharmacological targeting of these serine protease-dependent pathways may provide further protection from diabetic renal vascular disease.

Topics: Angiotensin I; Angiotensin II; Angiotensin-Converting Enzyme 2; Angiotensinogen; Animals; Arterioles; Diabetes Mellitus, Type 2; Diabetic Angiopathies; Disease Models, Animal; Kidney; Male; Mice; Mice, Mutant Strains; Peptidyl-Dipeptidase A; Rats; Rats, Sprague-Dawley; Receptors, Leptin; Serine Proteases; Signal Transduction; Vasoconstriction

Considering the growing importance of the interaction between components of kallikrein-kinin and renin-angiotensin systems in physiological and pathological processes, particularly in diabetes mellitus, the aim of the present study was to investigate the interaction between angiotensin-(1-7) (Ang-(1-7)) and bradykinin (BK), important components of these systems in an insulin resistance model of diabetes, and the effect of insulin on it. For this the response of mesenteric arterioles of anesthetized neonatal streptozotocin-induced (n-STZ) diabetic and control rats was evaluated using intravital microscopy. Though capable of potentiating BK in non-diabetic rats, Ang-(1-7) did not potentiate BK in n-STZ rats. Chronic but not acute insulin treatment restored the potentiation. This restorative effect of insulin was abolished by a K+ channel blocker (tetraethylammonium), by nitric oxide synthase inhibitor (N-nitro-L-arginine methyl ester) and by a cyclooxygenase inhibitor (indomethacin). On the other hand, Na(+)-,K(+)-ATPase inhibition (by ouabain) did not abolish the effect of insulin. There was no difference in mRNA and protein expression of B1 and B2 kinin receptor subtypes between n-STZ diabetic and control rats. Insulin treatment did not alter the kinin receptor expression. Our data allow us to conclude that diabetes impaired the interaction between BK and Ang-(1-7) and that insulin restores it. The restoring effect of insulin depends on membrane hyperpolarization, nitric oxide release and cyclooxygenease metabolites but not Na+K+-ATPase. Alteration of kinin receptor expression might not be involved in the restoring effect of insulin on the potentiation of BK by Ang-(1-7).

Topics: Angiotensin I; Animals; Animals, Newborn; Blood Glucose; Bradykinin; Diabetes Mellitus, Type 2; Drug Interactions; Gene Expression; Hypoglycemic Agents; Immunohistochemistry; Indomethacin; Insulin; Male; NG-Nitroarginine Methyl Ester; Ouabain; Peptide Fragments; Rats; Rats, Wistar; Receptors, Bradykinin; Reverse Transcriptase Polymerase Chain Reaction; Streptozocin; Tetraethylammonium; Vasodilation

The present study investigated the hypoglycemic action of des-aspartate-angiotensin I (DAA-I), a metabolite of angiotensin I, in two animal models of type 2 diabetes. The rationale was based on our earlier studies demonstrating that DAA-I acts on the angiotensin AT(1) receptor and exerts responses opposing those of angiotensin II and on recent reports that curtailment of angiotensin II formation by angiotensin converting enzyme inhibitors and blockade of the AT(1) receptor attenuate hyperglycemia in type 2 diabetics and diabetic animals. Diabetic KKAy mice and GK rats were administered orally (by gavage) one of the following doses of DAA-I: 400, 600, or 800 nmol/kg.d for 4 and 6 wk, respectively. Control diabetic animals were similarly administered water. Blood glucose of each animal was determined fortnightly by oral glucose tolerance test and blood insulin on the last day of treatment. Animals were killed, and the levels of plasma membrane glucose transporter-4 and cytosolic tyrosine-phosphorylated insulin receptor substrate-1 in hind limb skeletal muscles were determined by Western blot in insulin-challenged and nonchallenged animals. Orally administered DAA-I had no effect on blood insulin level but exerted dose-dependent hypoglycemic action in KKAy mice and GK rats after 4 and 6 wk of treatment, respectively. At the maximal effective dose of 600 nmol/kg, insulin induced a significant increase in plasma membrane glucose transporter-4 and cytosolic tyrosine-phosphorylated insulin receptor substrate-1. These findings show that DAA-I is not an insulin secretagogue and exerts hypoglycemic action by attenuating insulin resistance, the first such demonstration indicating that the nonapeptide is involved in glycemic regulation.

Topics: Angiotensin I; Animals; Blood Glucose; Blotting, Western; Body Weight; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 2; Glucose Tolerance Test; Glucose Transporter Type 4; Hypoglycemic Agents; Immunoprecipitation; Insulin; Insulin Resistance; Male; Mice; Mice, Inbred C57BL; Muscle, Skeletal; Phosphodiesterase I; Random Allocation; Rats; Rats, Wistar

Angiotensin II (Ang II) is able to induce free radical generation in neutrophils, which is more elevated in neutrophils of patients with hypercholesterolemia (HC). In addition, the signal processing through angiotensin I (Ang I) receptors is altered. In present study, we compared the Ang II-triggered free radical generation of neutrophils obtained from patients with relatively isolated forms of metabolic syndrome (MS) with membrane-bound cholesterol content and membrane fluidity. We determined the enhancement of Ang II-induced superoxide anion and leukotriene C(4) (LTC(4)) generation, membrane fluidity and cell-bound cholesterol content of neutrophils obtained from 12 control subjects, 11 patients with obesity (Ob), 10 patients with type 2 diabetes mellitus (t2-DM) and 12 patients with HC. The alteration of signal processing was studied after preincubation with different inhibiting drugs. Superoxide anion, LTC(4) production and membrane rigidity were increased in the following order: control < Ob < t2-DM < HC. Both Ang II-induced superoxide anion and LTC(4) generation were decreased in control cells by pertussis toxin and fluvastatin (Flu), whereas in each patient group, mepacrin, verapamil and Flu were effective, suggesting alterations in signal pathways, which may be attributed to isoprenylation. The enhancement of superoxide anion and LTC(4) generation correlated significantly with membrane rigidity, independently from the experimental groups and membrane-bound cholesterol content. Membrane rigidity of neutrophils, obtained from patients with MS, plays a role in Ang II-induced free radical generation independent of intracellular cholesterol homeostasis.

Topics: Adult; Angiotensin I; Angiotensin II; Anticholesteremic Agents; Cholesterol; Diabetes Mellitus, Type 2; Enzyme Inhibitors; Fatty Acids, Monounsaturated; Female; Fluvastatin; Homeostasis; Humans; Hypercholesterolemia; Indoles; Leukotriene C4; Male; Membrane Fluidity; Metabolic Syndrome; Middle Aged; Neutrophils; Pertussis Toxin; Protein Prenylation; Quinacrine; Signal Transduction; Superoxides; Vasoconstrictor Agents; Vasodilator Agents; Verapamil

Unlike the ubiquitous angiotensin-converting enzyme (ACE), the ACE-related carboxypeptidase 2 (ACE 2) is predominantly expressed in the heart, kidney, and testis. ACE 2 degrades angiotensin (Ang) II to Ang (1-7) and Ang I to Ang (1-9). We investigated the expression of ACE and ACE 2 in a rodent model of type 2 diabetes. ACE and ACE 2 were measured in kidney and heart from 8-week-old no diabetic control (db/m) mice and diabetic (db/db) mice, which at this young age have obesity and hyperglycemia without nephropathy. In renal cortical tissue, ACE mRNA was reduced (db/db 0.31+/-0.06 versus db/m 0.99+/-0.05; P<0.005), whereas ACE 2 mRNA was not (db/db 0.94+/-0.05 versus db/m 1.03+/-0.11, NS). ACE protein was markedly reduced in kidney cortex of db/db mice (db/db 0.24+/-0.13 versus db/m 1.02+/-0.12; P<0.005), and this was associated with a corresponding decrease in renal ACE activity (db/db 12.7+/-3.7 versus db/m 61.6+/-4.4 mIU/mg protein; P<0.001). ACE 2 protein, by contrast, was increased in kidneys from diabetic mice (db/db 1.39+/-0.14 versus db/m 0.53+/-0.04; P<0.005). An increase in ACE 2 protein and a decrease in ACE protein, respectively, were also seen by immunostaining of renal cortical tubules from the db/db mice. In heart tissue, there were no significant differences between db/db and db/m mice in either ACE mRNA and protein or ACE 2 mRNA and protein. We conclude that in young db/db mice, ACE 2 protein in renal cortical tubules is increased, whereas ACE protein is decreased. We propose that the pattern of low ACE protein coupled with increased ACE 2 protein expression may be renoprotective in early stages of diabetes.

Topics: Angiotensin I; Angiotensin II; Angiotensin-Converting Enzyme 2; Animals; Blood Glucose; Carboxypeptidases; Diabetes Mellitus, Type 2; Diabetic Nephropathies; Enzyme Induction; Kidney Tubules; Lipids; Lung; Membrane Proteins; Mice; Myocardium; Organ Size; Organ Specificity; Peptidyl-Dipeptidase A; Renin-Angiotensin System; RNA, Messenger

Our recent studies revealed a striking but variable enhancement of renal vasodilator responses to blockers of the renin-angiotensin system in subjects with diabetes mellitus, possibly reflecting the level of intrarenal activation of the renin-angiotensin system, and thus a risk of nephropathy. As obesity is a common finding in diabetic individuals, and obesity has been linked to an increase in plasma angiotensinogen levels, we enrolled diabetic subjects with a wide range of body mass index (BMI) for this study.. Twelve Type 2 diabetic subjects in balance on a low sodium diet participated after baseline renal plasma flow and glomerular filtration measurements were made. Each subject then received 150 mg irbesartan, and renal function was measured every 45 min for 4 h.. The average vasodilator response to irbesartan was 174 +/- 33 ml/min. No correlation was found between renal plasma flow response to irbesartan and duration of diabetes, baseline glucose, or HbA1c level. BMI, our measure of obesity, was highly correlated to the renal response to irbesartan (r = 0.7; P = 0.01).. Our findings suggest an important role for obesity in activating the intrarenal renin system, perhaps via production of angiotensinogen. BMI may be an indicator of risk of nephropathy.

Topics: Adult; Angiotensin I; Angiotensin Receptor Antagonists; Biphenyl Compounds; Blood Pressure; Body Mass Index; Diabetes Mellitus, Type 2; Diabetic Nephropathies; Female; Glomerular Filtration Rate; Humans; Irbesartan; Linear Models; Male; Middle Aged; Obesity; Renal Circulation; Renin-Angiotensin System; Risk Factors; Tetrazoles; Vasodilator Agents

Recently, the obese Zucker rat (OZR), an animal model of non-insulin-dependent (type II) diabetes, was shown to respond to converting enzyme inhibition with decreased albuminuria and a marked attenuation of glomerular injury. It was hypothesized that the OZR would possess low plasma renin values and an increased vascular responsiveness to angiotensin II, and therefore, the renin-angiotensin system (PRA, active renin, inactive renin, renal renin content, and plasma angiotensinogen) and vascular reactivity in OZR at 10 and 24 wk of age were investigated. PRA and renin concentration, inactive plasma renin, and renal renin content were all significantly (P < 0.05) reduced in OZR when compared with age-matched lean controls. The ratio of inactive to total renin was significantly increased in the OZR. OZR aortic ring vascular reactivity to KCl, norepinephrine, and angiotensin II was assessed. Despite essentially equal or increased contractile responses to KCl and norepinephrine at both 10 and 24 wk of age, the OZR was not more sensitive to angiotensin II and displayed a significantly reduced contractile response to angiotensin II at 24 wk of age, when compared with lean age-matched controls. It was concluded that the renal protective effect of converting enzyme inhibition in OZR, despite significantly reduced PRA and concentration, inactive plasma renin, and renal renin content, may not be due to a diabetes-induced increased vascular reactivity to angiotensin II.

Topics: Angiotensin I; Angiotensin II; Animals; Aorta; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 2; In Vitro Techniques; Male; Norepinephrine; Obesity; Rats; Rats, Zucker; Renin; Renin-Angiotensin System; Vasoconstriction