The vasodilator action of insulin. Implications for the insulin hypothesis of hypertension

Maternal Hyperglycemia Induces Autonomic Dysfunction and Heart Failure in Older Adult Offspring

AIMS

Offspring exposed to an adverse fetal environment, such as gestational diabetes, may manifest increased susceptibility to several chronic diseases later in life. In the present study, the cardiovascular function of three different ages of offspring from diabetic rats was evaluated.

METHODS AND RESULTS

Diabetes mellitus was induced in pregnant rats by a single dose of streptozotocin (50 mg/kg). The offspring from diabetic (OD) and control rats (OC) were evaluated at three different ages: 6, 12 or 18 months. In the corresponding OC groups, fasting glycemia, baseline mean arterial pressure, and sympathetic tonus increased in the OD rats at 12 (OD12) and 18 (OD18) months of age, while cardiac hypertrophy was observed in all OD groups. Cardiac function evaluation in vivo showed low left ventricular systolic pressure and+dP/dt in the OD18 rats, suggesting a systolic dysfunction. OD12 and OD18 groups showed high left ventricle end-diastolic pressure, suggesting a diastolic dysfunction. OD groups showed an age-related impairment of both baroreflex-mediated tachycardia and baroreflex-mediated bradycardia in OD12 and OD18 rats. In isolated hearts from OD18 rats, both inotropic and tachycardiac responses to increasing isoproterenol were significantly reduced compared to the corresponding OC group.

CONCLUSION

These results suggest that gestational diabetes triggers the onset of hyperglycemia hypertension with impaired baroreflex sensitivity and heart failure in older age of offspring, representing important risk factors for death. Therefore, ensuring optimal glycemic control in diabetic pregnancy is important and serves as a key to preventing cardiovascular disease in the offspring in their older age.

Asymptomatic postprandial hypotension in patients with diabetes: The KAMOGAWA-HBP study

AIMS/INTRODUCTION

Postprandial hypotension (PPH) refers to a decrease in systolic blood pressure by ≥20 or to <90 mmHg from baseline ≥100 mmHg within 2 h of a meal. Previous studies have reported an association between diabetes and PPH; however, the characteristics of PPH in patients with diabetes remain unclear.

MATERIALS AND METHODS

We recruited patients with diabetes who regularly attended the diabetes outpatient clinic. Participants were instructed to carry out three sets of blood pressure measurements at six time points: just before and right after, and 30, 60, 90 and 120 min after their main meal of the day. Data on PPH symptoms were collected during an interview. To investigate the relationships between explanatory variables, PPH and associated symptoms, we carried out multiple logistic regression analyses.

RESULTS

We analyzed data from 300 participants. There were 150 (50.0%) participants with PPH. Systolic blood pressure before a meal was significantly associated with PPH (odds ratio [OR] 1.56, 95% confidence interval [CI] 1.30-1.86, P < 0.001), after adjusting for covariates. Furthermore, age (OR 1.08, 95% CI 1.01-1.16, P = 0.027), hemoglobin A1c level (OR 2.39, 95% CI 1.01-5.64, P = 0.030) and coefficients of variation of R-R intervals (OR 0.79, 95% CI 0.65-0.97, P = 0.032) were significantly associated with asymptomatic PPH.

CONCLUSIONS

Half of the present study outpatients with diabetes had PPH. High systolic blood pressure before a meal was significantly associated with the risk of PPH. Older adults and patients with higher levels of hemoglobin A1c or an autonomic dysfunction might have difficulties recognizing symptoms of PPH.

Diabetes, and its treatment, as an effector of autonomic nervous system circuits and its functions

Diabetes increases the risk of cardiovascular complications, including heart failure, hypertension, and stroke. There is a strong involvement of autonomic dysfunction in individuals with diabetes that exhibit clinical manifestations of cardiovascular diseases (CVD). Still, the mechanisms by which diabetes and its treatments alter autonomic function and subsequently affect cardiovascular complications remain elusive. For this reason, understanding the brainstem circuits involved in sensing metabolic state(s) and enacting autonomic control of the cardiovascular system are important to develop more comprehensive therapies for individuals with diabetes at increased risk for CVD. We review how autonomic nervous system circuits change during these disease states and discuss their potential role in current pharmacotherapies that target diabetic states. Overall, this review proposes that the brainstem circuits provide an integrative sensorimotor network capable of responding to metabolic cues to regulate cardiovascular function and this network is modified by, and in turn affects, diabetes-induced CVD and its treatment.

Out-of-Clinic Sympathetic Activity Is Increased in Patients With Masked Uncontrolled Hypertension

Masked uncontrolled hypertension (MUCH) is defined as controlled automated office blood pressure (BP; AOBP <135/85 mm Hg) in-clinic in patients receiving antihypertensive medication(s) but uncontrolled BP out-of-clinic by 24-hour ambulatory BP monitoring (ABPM; awake ≥135/85 mm Hg). We hypothesized that MUCH patients have greater out-of-clinic sympathetic activity compared with true controlled hypertensives. Patients being treated for hypertension were prospectively recruited after 3 or more consecutive clinic visits. All patients were evaluated by in-clinic automated office BP, plasma catecholamines, and spot-urine/plasma metanephrines. In addition, out-of-clinic 24-hour ABPM, 24-hour urinary for catecholamines and metanephrines was done. Out of 237 patients recruited, 169 patients had controlled in-clinic BP of which 156 patients had completed ABPM. Seventy-four were true controlled hypertensives, that is controlled by clinic automated office BP and by out-of-clinic ABPM. The remaining 82 were controlled by clinic automated office BP, but uncontrolled during out-of-clinic ABPM, indicative of MUCH. After exclusion of 4 patients because of inadequate or lack of 24-hour urinary collections, 72 true controlled hypertensive and 80 MUCH patients were analyzed. MUCH patients had significantly higher out-of-clinic BP variability and lower heart rate variability compared with true controlled hypertensives, as well as higher levels of out-of-clinic urinary catecholamines and metanephrines levels consistent with higher out-of-clinic sympathetic activity. In contrast, there was no difference in in-clinic plasma catecholamines and spot-urine/plasma levels of metanephrines between the 2 groups, consistent with similar levels of sympathetic activity while in clinic. MUCH patients have evidence of heightened out-of-clinic sympathetic activity compared with true controlled hypertensives, which may contribute to the development of MUCH.

Caloric Restriction and Its Effect on Blood Pressure, Heart Rate Variability and Arterial Stiffness and Dilatation: A Review of the Evidence

Essential hypertension, fast heart rate, low heart rate variability, sympathetic nervous system dominance over parasympathetic, arterial stiffness, endothelial dysfunction and poor flow-mediated arterial dilatation are all associated with cardiovascular mortality and morbidity. This review of randomised controlled trials and other studies demonstrates that caloric restriction (CR) is capable of significantly improving all these parameters, normalising blood pressure (BP) and allowing patients to discontinue antihypertensive medication, while never becoming hypotensive. CR appears to be effective regardless of age, gender, ethnicity, weight, body mass index (BMI) or a diagnosis of metabolic syndrome or type 2 diabetes, but the greatest benefit is usually observed in the sickest subjects and BP may continue to improve during the refeeding period. Exercise enhances the effects of CR only in hypertensive subjects. There is as yet no consensus on the mechanism of effect of CR and it may be multifactorial. Several studies have suggested that improvement in BP is related to improvement in insulin sensitivity, as well as increased nitric oxide production through improved endothelial function. In addition, CR is known to induce SIRT1, a nutrient sensor, which is linked to a number of beneficial effects in the body.

Oral health and coronary heart disease

BACKGROUND

It is well documented that there is some correlation between poor oral health in the form of periodontal disease and coronary heart disease (CHD). It is unclear whether this correlation is due to a causal relationship or shared underlying disorder such as inflammation. A suitable integrated model of the CHD pathogenetic pathways relevant to periodontal disease may help to elucidate the association. Such a model is currently not available in literature.

METHODS

A previously developed integrated model of CHD was used to investigate potential pathogenetic pathways linking periodontal disease to CHD biomarkers.

RESULTS

The integrated model was created to provide insight into possible higher-order biological interactions underlying CHD and periodontal disease. In order to simplify these interactions a novel 'connection graph' was developed. It quantitatively illustrates the relationship between periodontal disease and various serological biomarkers of CHD. The pathogenesis of periodontitis shows various possible pathways which could link periodontitis to CHD pathogenesis.

CONCLUSION

An integrated model of CHD was developed which provides a summary of the potential CHD effects of periodontal disease. Further research must refine and validate the model.

The sympathetic nervous system alterations in human hypertension

Several articles have dealt with the importance and mechanisms of the sympathetic nervous system alterations in experimental animal models of hypertension. This review addresses the role of the sympathetic nervous system in the pathophysiology and therapy of human hypertension. We first discuss the strengths and limitations of various techniques for assessing the sympathetic nervous system in humans, with a focus on heart rate, plasma norepinephrine, microneurographic recording of sympathetic nerve traffic, and measurements of radiolabeled norepinephrine spillover. We then examine the evidence supporting the importance of neuroadrenergic factors as promoters and amplifiers of human hypertension. We expand on the role of the sympathetic nervous system in 2 increasingly common forms of secondary hypertension, namely hypertension associated with obesity and with renal disease. With this background, we examine interventions of sympathetic deactivation as a mode of antihypertensive treatment. Particular emphasis is given to the background and results of recent therapeutic approaches based on carotid baroreceptor stimulation and radiofrequency ablation of the renal nerves.

Novel mechanism of blood pressure regulation by forkhead box class O1-mediated transcriptional control of hepatic angiotensinogen

The renin-angiotensin system is a major determinant of blood pressure regulation. It consists of a cascade of enzymatic reactions involving 3 components: angiotensinogen, renin, and angiotensin-converting enzyme, which generate angiotensin II as a biologically active product. Angiotensinogen is largely produced in the liver, acting as a major determinant of the circulating renin-angiotensin system, which exerts acute hemodynamic effects on blood pressure regulation. How the expression of angiotensinogen is regulated is not completely understood. Here, we hypothesize that angiotensinogen is regulated by forkhead transcription factor forkhead box class O1 (Foxo1), an insulin-suppressed transcription factor, and thereby controls blood pressure in mice. We generated liver-specific Foxo1 knockout mice, which exhibited a reduction in plasma angiotensinogen and angiotensin II levels and a significant decrease in blood pressure. Using hepatocyte cultures, we demonstrated that overexpression of Foxo1 increased angiotensinogen expression, whereas hepatocytes lacking Foxo1 demonstrated a reduction of angiotensinogen gene expression and partially impaired insulin inhibition on angiotensinogen gene expression. Furthermore, mouse angiotensinogen prompter analysis demonstrated that the angiotensinogen promoter region contains a functional Foxo1-binding site, which is responsible for both Foxo1 stimulation and insulin suppression on the promoter activity. Together, these data demonstrate that Foxo1 regulates hepatic angiotensinogen gene expression and controls plasma angiotensinogen and angiotensin II levels, modulating blood pressure control in mice.

Modeling the autonomic and metabolic effects of obstructive sleep apnea: a simulation study

Long-term exposure to intermittent hypoxia and sleep fragmentation introduced by recurring obstructive sleep apnea (OSA) has been linked to subsequent cardiovascular disease and Type 2 diabetes. The underlying mechanisms remain unclear, but impairment of the normal interactions among the systems that regulate autonomic and metabolic function is likely involved. We have extended an existing integrative model of respiratory, cardiovascular, and sleep-wake state control, to incorporate a sub-model of glucose-insulin-fatty acid regulation. This computational model is capable of simulating the complex dynamics of cardiorespiratory control, chemoreflex and state-related control of breath-to-breath ventilation, state-related and chemoreflex control of upper airway potency, respiratory and circulatory mechanics, as well as the metabolic control of glucose-insulin dynamics and its interactions with the autonomic control. The interactions between autonomic and metabolic control include the circadian regulation of epinephrine secretion, epinephrine regulation on dynamic fluctuations in glucose and free-fatty acid in plasma, metabolic coupling among tissues and organs provided by insulin and epinephrine, as well as the effect of insulin on peripheral vascular sympathetic activity. These model simulations provide insight into the relative importance of the various mechanisms that determine the acute and chronic physiological effects of sleep-disordered breathing. The model can also be used to investigate the effects of a variety of interventions, such as different glucose clamps, the intravenous glucose tolerance test, and the application of continuous positive airway pressure on OSA subjects. As such, this model provides the foundation on which future efforts to simulate disease progression and the long-term effects of pharmacological intervention can be based.

Melanocortin signalling and the regulation of blood pressure in human obesity

Obesity has reached epidemic proportions worldwide. Sympathetic nervous system activation has been shown to play a major role linking obesity to the development of associated metabolic complications, such as hypertension. Recent evidence has implicated central melanocortin signalling in the regulation of blood pressure in rodents and humans. The importance of sympathetic neural activity in mediating this association has been highlighted. Humans with loss-of-function mutations in the melanocortin 4 receptor (MC4R) are an ideal group of subjects in whom the importance of melanocortin signalling in linking obesity to hypertension can be studied. Consistent with rodent studies, it was recently demonstrated that humans with MC4R deficiency have lower blood pressure, less hypertension, lower 24-h urinary catecholamine excretion, lower resting heart rate and attenuated insulin-mediated sympathetic activation compared to equally-obese humans. In overweight and obese humans without MC4R mutations, the infusion of a highly-selective MC4R agonist led to dose-dependent increases in blood pressure and heart rate. All effects were independent of insulin. This evidence supports the notion that the melanocortin system regulates blood pressure and sympathetic neural function. The results obtained in rodent and human studies, in relation to blood pressure and sympathetic function, may limit the use of MC4R agonists for the treatment of obesity. Future studies will determine whether MC4R deficiency is associated with protection from development of the detrimental cardiovascular consequences that accompany obesity.

The effects of thiazolidinediones on blood pressure levels – A systematic review

Insulin resistance has been proposed to be the underlying disorder of the so-called metabolic or insulin resistance syndrome, which represents the clustering in the same individual of several cardiovascular risk factors, such as type 2 diabetes mellitus, hypertension, abdominal obesity, elevated triglycerides and low high-density lipoprotein-cholesterol. As far as the connection of insulin resistance and compensatory hyperinsulinaemia with hypertension is concerned, a number of mechanisms possibly linking these disturbances have been described, such as activation of sympathetic nervous system, enhancement of renal sodium reabsorption, or impairment of endothelium-dependent vasodilatation. Thiazolidinediones (TZDs) constitute a class of oral antihyperglycaemic agents that act by decreasing insulin resistance, and apart from their action on glycaemic control, they have been also reported to exert beneficial effects on other parameters of the metabolic syndrome. In particular, during recent years a considerable number of animal and human studies have shown that the use of TZDs was associated with usually small but significant reductions of blood pressure (BP) levels. Since a possible beneficial action of these compounds on BP could be of particular value for patients with the metabolic syndrome, this review aimed to summarize and evaluate the literature data in the field, derived either from studies that just examined BP levels among other parameters or from studies that were specifically designed to determine the effect of a TZD on BP.

Impact of abdominal fat and insulin resistance on arterial hypertension in non-obese women

OBJECTIVE: To evaluate the impact of abdominal fat and insulin resistance on arterial hypertension of non-obese women. METHODS:Thirty-five non-obese women (NO), age 35-68 years were studied, and divided into two groups according to the presence of hypertension (BP > 140 x 90 mmHg) ( HT = hypertensive; NT = normotensive). Leptin measurement and oral glucose tolerance test (OGTT) to assess insulin were performed in these patients. A CT-scan was used to evaluate visceral (VF) and subcutaneous abdominal fat (SCF). The Central fat distribution index (CDI) was proposed to evaluate the impact of subcutaneous abdominal fat on central fat distribution in hypertensive patients. RESULTS: When compared to NT-NO (n = 17) group, HT-NO (n = 18) showed higher blood pressure levels (systolic and diastolic), greater VF area (84.40 ± 55.70 versus 37.50 ± 23.00 cm²; p = 0.036), greater SCF area (174.30 ± 83.00 versus 79.80 ± 27.40 cm²; p = 0.030), higher HOMAr index (1.59 ± 0.72 versus 0.93 ± 0.48 mmol.mU/L²; p = 0.006), higher CDI index (12.67 ± 7.04 versus 6.19 ± 2.57 cm²/kg) and higher leptin level (19.1 ± 9.6 versus 7.4 ± 3.5 ng/mL; p = 0.028). CONCLUSIONS: Arterial hypertension in non-obese women is associated with insulin resistance, central fat distribution and higher leptin levels.

Hot flashes and fatigue relieved by metformin

OBJECTIVE

To describe 3 patients with long-standing hot flashes, excessive sweating, and fatigue whose symptoms were ameliorated with metformin.

METHODS

In this case series, we report the findings of laboratory evaluations, including assessments for thyroid, gonadal, adrenal, and pancreatic disorders, in 3 patients referred for endocrine evaluation. A 75-g oral glucose tolerance test with measurement of fasting and postprandial glucose and insulin concentrations was conducted. A trial of metformin, 500 mg twice daily, was initiated in all patients.

RESULTS

Evaluation of factors that are associated with hot flashes and increased sweating did not establish the cause of the patients' symptoms. The 3 patients had normal glucose tolerance test results and hyperinsulinemia. Metformin therapy markedly relieved the symptoms in all patients.

CONCLUSIONS

Hyperinsulinemia without hypoglycemia may produce a sympathoexcitatory response that manifests as hot flashes and increased sweating. Metformin may have sympathoinhibitory actions that alleviate these symptoms.

Metabolic syndrome and incidence of type 2 diabetes in patients with manifest vascular disease

Risk reduction in patients with clinically manifest vascular disease focuses on preventing new vascular events and not on prevention of type 2 diabetes. However, given the common pathophysiological pathways involved in the development of atherosclerosis and type 2 diabetes, it is probable that people with atherosclerotic vascular disease have an elevated risk of type 2 diabetes. The present prospective cohort study investigated the incidence of type 2 diabetes and the effect of the presence of metabolic syndrome on the incidence of type 2 diabetes in 4,022 patients with clinically manifest atherosclerosis, included in the study from September 1996 to June 2006. Patients who died (n=456), who were lost to follow-up (n=84) and those with diabetes at baseline (n=558) were excluded, leaving 2,924 patients for analysis. The incidence of diabetes was assessed by questionnaire (self-reported diabetes). During 13,726 person-years of follow-up (median follow-up 4.3 years, range 2.4-7.0 years), there were 152 type 2 diabetes cases (5.2%), corresponding to an incidence rate of 11.1 (95% CI 9.4-13.0) per 1,000 person-years. Patients with metabolic syndrome were at increased risk of incident type 2 diabetes compared to those without metabolic syndrome, with an adjusted hazard ratio of 5.7 (95% CI 3.7-8.9) for Revised National Cholesterol Education Program, 6.0 (4.1-9.0) for National Cholesterol Education Program and 4.0 (2.7-6.1) for International Diabetes Federation definitions of metabolic syndrome. Of all metabolic syndrome components, abdominal obesity was most strongly associated with incident type 2 diabetes (94% higher risk of type 2 diabetes for 1 standard deviation (11.3 cm) increase in waist circumference). In conclusion, patients with manifest atherosclerosis are at high risk of developing type 2 diabetes. Metabolic syndrome identifies those at the highest risk and is an easy to use clinical tool. Abdominal obesity is a strong individual predictor of type 2 diabetes. Patients with manifest atherosclerosis and metabolic syndrome may derive particular benefit from lifestyle interventions focusing on weight reduction.

Insulin activates ATP-sensitive potassium channels via phosphatidylinositol 3-kinase in cultured vascular smooth muscle cells

The effects of insulin on the vasculature are significant because insulin resistance is associated with hypertension. To increase the understanding of the effects of insulin on the vasculature, we analyzed changes in potassium ion transport in cultured vascular smooth muscle cells (VSMCs). Using the potential-sensitive fluorescence dye bis-(1,3-dibutylbarbituric acid)trimethine oxonol [DiBAC4(3)], we found that insulin induced membrane hyperpolarization after 2 min in A10 cells. Insulin-induced hyperpolarization was suppressed by glibenclamide, an ATP-sensitive potassium (K(ATP)) channel blocker. Using a cell-attached patch clamp experiment, the K(ATP) channel was activated by insulin in both A10 cells and isolated VSMCs from rat aortas, indicating that insulin causes membrane hyperpolarization via K(ATP) channel activation. These effects were not dependent on intracellular ATP concentration, but wortmannin, a phosphatidylinositol 3-kinase (PI3-K) inhibitor, significantly suppressed insulin-induced K(ATP) channel activation. In addition, insulin enhanced phosphorylation of insulin receptor, insulin receptor substrate (IRS)-1 and protein kinase B (Akt) after 2 min. These data suggest that K(ATP) channel activation by insulin is mediated by PI3-K. Furthermore, using a nitric oxide synthase (NOS) inhibitor, we found that NOS might play an important role downstream of PI3-K in insulin-induced K(ATP) channel activation. This study may contribute to our understanding of mechanisms of insulin resistance-associated hypertension.

Lower bone mineral content in hypertensive compared with normotensive overweight Latino children and adolescents

BACKGROUND

In adults, hypertension has been shown to be inversely correlated with bone mineral content (BMC); however, the association between blood pressure (BP) and BMC has not been studied in pediatrics.

METHODS

Total body BMC of 187 overweight (mean BMI = 28.7 kg/m(2)) Latino children and adolescents (mean age = 11.2 years) were measured using dual-energy x-ray absorptiometry. Seated systolic BP (SBP) and diastolic BP (DBP) were measured using a standard mercury sphygmomanometer. Hypertension was defined by SBP or DBP above the 90(th) percentile for height, age, and sex.

RESULTS

Partial correlations revealed an inverse association between SBP and BMC (r = -0.24, P = 0.02) in boys (n = 105); results were nonsignificant (P = 0.27) in girls (n = 82). There were no significant correlations between DBP and BMC. When BMI and insulin sensitivity were adjusted for, hypertensive boys (n = 21) had lower BMC (1435 v 1636 g; P = 0.03) than normotensive boys (n = 84); similarly, hypertensive girls (n = 25) had lower BMC (1438 v 1618 g; P = 0.02) than normotensive girls (n = 57). In postpubertal adolescents (Tanner stage 4-5; n = 48), inverse correlations were stronger (r = -0.40, P = 0.007); results were nonsignificant in prepubertal and pubertal children (Tanner stage 1-3; n = 139, P = 0.57). In postpubertal girls (n = 37), there were no significant correlations (P = 0.14); inverse correlations in postpubertal boys (n = 11) became markedly stronger (r = -0.80, P = 0.02).

CONCLUSION

Based on the study findings, SBP is inversely correlated with BMC in overweight adolescents; additionally, hypertensive subjects have lower adjusted means of BMC than normotensive subjects. These promising new findings suggest that hypertension may be a risk factor for osteopenia in overweight children and adolescents; this risk may be exacerbated in postpubertal boys.

The metabolic syndrome: metabolic changes with vascular consequences

Despite criticism regarding its clinical relevance, the concept of the metabolic syndrome improves our understanding of both the pathophysiology of insulin resistance and its associated metabolic changes and vascular consequences. Free fatty acids (FFA) and tumour necrosis factor-alpha (TNF-alpha) play prominent roles in the development of insulin resistance by impairing the intracellular insulin signalling transduction pathway. Obesity is an independent risk factor for cardiovascular disease and strongly related to insulin resistance. In case of obesity, FFAs and TNF-alpha are produced in abundance by adipocytes, whereas the production of adiponectin, an anti-inflammatory adipokine, is reduced. This imbalanced production of pro- and anti-inflammatory adipokines, as observed in adipocyte dysfunction, is thought to be the driving force behind insulin resistance. The role of several recently discovered adipokines such as resistin, visfatin and retinol-binding protein (RBP)-4 in the pathogenesis of insulin resistance is increasingly understood. Insulin resistance induces several metabolic changes, including hyperglycaemia, dyslipidaemia and hypertension, all leading to increased cardiovascular risk. In addition, the dysfunctional adipocyte, reflected largely by low adiponectin levels and a high TNF-alpha concentration, directly influences the vascular endothelium, causing endothelial dysfunction and atherosclerosis. Adipocyte dysfunction could therefore be regarded as the common antecedent of both insulin resistance and atherosclerosis and functions as the link between obesity and cardiovascular disease. Targeting the dysfunctional adipocyte may reduce the risk for both cardiovascular disease and the development of type 2 diabetes. Although lifestyle intervention remains the cornerstone of therapy in improving insulin sensitivity and its associated metabolic changes, medical treatment might prove to be important as well.

Inhibitory effect of insulin on vasopressin-induced intracellular calcium response is blunted in hyperinsulinemic hypertensive patients: role of membrane fatty acid composition

Impaired insulin-mediated vasodilation has been implicated in hypertension that is associated with the metabolic syndrome. The aim of this study was to determine whether an abnormality in membrane fatty acid composition was related to a weakening of insulin's inhibitory effect on agonist-stimulated intracellular free calcium elevation. Mild to moderate hypertensive patients (n = 27) and normotensive controls (n = 11) were studied. Hypertensive patients were divided into normoinsulinemic patients (n = 14) and hyperinsulinemic patients (n = 13) according to the area under the curve of plasma insulin concentrations during a 75-g oral glucose tolerance test. Nonstimulated and arginine-vasopressin (AVP) (1 micromol/l)-stimulated intraplatelet free calcium concentrations (p[Ca(2+)](i)) were measured with or without insulin (100 microU/ml) preincubation. Platelet membrane fatty acid composition, intraerythrocyte sodium content, and the ouabain-sensitive sodium efflux rate constant (K (os)) of erythrocytes were also determined. Insulin preincubation reduced AVP-stimulated p[Ca(2+)](i) elevation in both normotensive controls and hypertensive patients. The inhibitory effect of insulin on AVP-stimulated elevation of p[Ca(2+)](i) (%Inhibition) was significantly (P < 0.05) blunted in hyperinsulinemic hypertensive patients (9.7% +/- 2.4%) as compared to normoinsulinemic hypertensive patients (17.4% +/- 2.7%) and normotensive controls (16.9% +/- 1.7%). In hypertensive patients, the %Inhibition was correlated negatively with saturated fatty acids (SFA) (r = -0.51, P < 0.05) and systolic blood pressure (r = -0.44, P < 0.05), and correlated positively with membrane polyunsaturated fatty acids (PUFA) (r = 0.53, P < 0.01) and K (os) (r = 0.53, P < 0.005). Multiple regression analysis showed that SFA, PUFA, and K (os) were the significant variables for %Inhibition. These findings indicate that an increase in SFA and a decrease in PUFA may cause insulin insensitivity in cellular calcium and sodium handling in hypertension with hyperinsulinemia.

AKT phosphorylation is essential for insulin-induced relaxation of rat vascular smooth muscle cells

Insulin resistance, a major factor in the development of type 2 diabetes, is known to be associated with defects in blood vessel relaxation. The role of Akt on insulin-induced relaxation of vascular smooth muscle cell (VSMC) was investigated using siRNA targeting Akt (siAKTc) and adenovirus constructing myristilated Akt to either suppress endogenous Akt or overexpress constitutively active Akt, respectively. siAKTc decreased both basal and insulin-induced phosphorylations of Akt and glycogen synthase kinase 3beta, abolishing insulin-induced nitric oxide synthase (iNOS) expression. cGMP-dependent kinase 1alpha (cGK1alpha) and myosin-bound phosphatase (MBP) activities, both downstream of iNOS, were also decreased. siAKTc treatment resulted in increased insulin and ANG II-stimulated phosphorylation of contractile apparatus, such as MBP substrate (MYPT1) and myosin light chain (MLC20), accompanied by increased Rho-associated kinase alpha (ROKalpha) activity, demonstrating the requirement of Akt for insulin-induced vasorelaxation. Corroborating these results, constitutively active Akt upregulated the signaling molecules involved in insulin-induced relaxation such as iNOS, cGK1alpha, and MBP activity, even in the absence of insulin stimulation. On the contrary, the contractile response involving the phosphorylation of MYPT1 and MLC20, and increased ROKalpha activity stimulated by ANG II were all abolished by overexpressing active Akt. In conclusion, we demonstrated here that insulin-induced VSMC relaxation is dependent on Akt activation via iNOS, cGK1alpha, and MBP activation, as well as the decreased phosphorylations of MYPT1 and MLC20 and decreased ROKalpha activity.

Can PPARgamma agonists have a role in the management of obesity-related hypertension?

Peroxisome proliferator-activated receptors (PPAR) are ligand-activated transcription factors belonging to the nuclear hormone receptor superfamily. PPARgamma is the most extensively studied amongst the three subtypes (alpha, delta and gamma). This receptor is a key modulator of lipid and glucose homeostasis and is predominantly expressed in adipose tissue. Expression of PPARgamma is also found in non-adipose tissues including heart, kidney, spleen, and interestingly, in all relevant components of the vasculature: endothelial and smooth muscle cells. These receptors may therefore also play a role in the regulation of vascular tone and blood pressure. Genetic variants of PPARgamma have also been associated with features of the metabolic syndrome, including obesity and increased blood pressure. The discovery of synthetic ligands for PPARgamma, the Thiazolidinediones (TZDs) has greatly enhanced our understanding of their ligand dependent activation and more importantly their role in vascular pathobiology. Approximately 10 years ago, serendipitous animal experiments demonstrated that despite causing sodium retention, the TZDs actually lowered blood pressure. This review will highlight the role of TZDs in various models of hypertension and discuss their potential role in the management of obesity-related hypertension.

Enhanced sympathetic reactivity associates with insulin resistance in the young Zucker rat

Somatosympathetic reflexes were studied in young hyperinsulinemic, insulin-resistant (Zucker fatty) rats (ZFR) and a related control (Zucker lean) strain (ZLR). Glucose metabolism was characterized by minimal model analysis of intravenous glucose tolerance test data. Seven-week-old ZFR (n=18) and ZLR (n=17) were studied under pentobarbital anesthesia. Mean body weight and plasma glucose and insulin concentration were significantly greater (P<0.05) in ZFR than in ZLR, whereas basal values of mean arterial pressure (MAP) and heart rate (HR) were not significantly different. Increments of MAP (DeltaMAP) and HR (DeltaHR) elicited by electrical stimulation of the sciatic nerve (5-s trains of 100 pulses, 0.5-ms pulse duration, 100- to 400-microA pulse intensity) were significantly higher (ANOVA, P<0.05) in ZFR at each level of stimulus intensity. Regression analysis showed a linear increase in DeltaMAP and DeltaHR with increasing sciatic nerve stimulus intensity. Pressor responses to phenylephrine after ganglionic blockade demonstrated that vascular reactivity to adrenergic stimulation is not increased in ZFR compared with ZLR. Thus this factor does not contribute to enhancement of somatosympathetic reflexes observed in this strain. Insulin sensitivity in ZFR was one-fourth (P<0.05) that in ZLR. These results suggest that stronger sympathetic nervous reactivity in ZFR is associated with a severe insulin-resistant state before the onset of hypertension and support the hypothesis that insulin-mediated stimulation of the sympathetic nervous system is involved in the development of cardiovascular diseases related to alterations of glucose metabolism.

Effect of insulin on small intestinal transit in normal mice is independent of blood glucose level

Background

Insulin is the drug of choice in the management of diabetes mellitus (DM). About 76 % of diabetic patients suffer from gastrointestinal (GI) disorders. Therapy of DM with insulin primarily involves lowering of elevated blood glucose levels. Hence, on any organ in addition to insulin's effect, hypoglycaemic effect also prevails. A systematic study exploring the effect of insulin on small intestinal transit in normal laboratory animals is lacking. Hence, in the present study, the possible effect of insulin with or without associated hypoglycaemia on small intestinal transit in normal mice was examined.

Results

Insulin in all the doses tested (2 μ, 2 m and 2 U/kg) elicited a significant acceleration of SIT. The lower doses of insulin (2 μ and 2 m U/kg) produced significant acceleration of SIT and were associated with normal blood glucose levels. However, the highest dose of insulin (2 U/kg) produced an acceleration of SIT that was associated with significant fall in blood glucose levels. Further, the 2 m and 2 U doses of insulin significantly elevated serum insulin and C-peptide levels.

Conclusion

Insulin at the lowest dose produced an acceleratory effect on SIT that was independent of blood glucose and serum insulin levels in normal mice.

Intrauterine exposure to diabetes is a determinant of hemoglobin A(1)c and systolic blood pressure in pima Indian children

CONTEXT/OBJECTIVE

Given the increasing rates of both childhood obesity and type 2 diabetes (T2DM), we investigated whether maternal diabetes status during pregnancy is a determinant of risk factors associated with T2DM or cardiovascular disease in offspring during childhood.

DESIGN/PARTICIPANTS

Forty-two Pima Indians, aged 7-11 yr, were identified retrospectively from maternal oral glucose tolerance tests as offspring of a diabetic pregnancy (22 ODM, eight males, 14 females) or offspring born before the mother developed diabetes (20 PRE, 12 males, eight females). SETTING/MAIN OUTCOME MEASURES: Weight, height, body mass index, percent body fat, blood pressure, and fasting concentrations of glucose, insulin, hemoglobin A1c (HbA1c), total cholesterol, triglycerides, and high-density lipoprotein-cholesterol were measured while staying in an in-patient clinical research unit and compared in cross-sectional analyses.

RESULTS

After adjustment for age and gender, ODM had significantly higher concentrations of HbA1c (ODM = 5.7 +/- 0.4, PRE = 5.0 +/- 0.4%, P = 0.002), higher systolic (SBP) blood pressure (ODM = 118 +/- 13, PRE = 107 +/- 10 mm Hg; P = 0.02), and lower concentrations of high-density lipoprotein (ODM = 41 +/- 9, PRE = 48 +/- 6 mg/dl, P = 0.03) than PRE. Maternal diabetes status during pregnancy persisted as a significant determinant of SBP (beta = 7.50, P = 0.03) and HbA1c (beta = 0.43, P = 0.002), independent of age, gender, and percent body fat.

CONCLUSION

Intrauterine exposure to diabetes is a significant determinant of higher SBP and HbA1c during childhood, independent of adiposity and a genetic predisposition to T2DM. These data suggest that in utero exposure to diabetes confers an additional independent risk for the development of T2DM and/or cardiovascular disease later in life.

Changes in blood pressure and plasma catecholamine levels during prolonged hyperinsulinemia

Hyperinsulinemia has been shown to induce activation of the sympathetic nervous system and vasodilatation. Whether these effects result in changes in blood pressure (BP) is discussed controversially. We measured BP and plasma catecholamine levels in 30 healthy men during a 60-minute baseline phase and 360-minute period of insulin infusion. In a double-blind, between-subject comparison, insulin was infused at a low rate (1.5 mU insulin/kg per minute) in one half of the subjects and at a high rate (15 mU/kg per minute) in the other half. Throughout the experiments, blood glucose levels were held constantly within the normal range by a simultaneous infusion of glucose. Serum insulin levels increased to a plateau of 543 +/- 34 pmol/L during low rate and to 24,029 +/- 1,595 pmol/L during high rate of insulin infusion. Compared with baseline, insulin infusion of either rate significantly increased systolic BP, BP amplitude, and heart rate (all P < .05). In comparison with the low rate of insulin infusion, the high rate provoked a more pronounced increase in heart rate (P < .02) and systolic BP (P < .05) but tended to decrease diastolic BP (P < .08) summing up to a distinctly more increased BP amplitude (P < .05). Plasma norepinephrine as well as epinephrine levels did not significantly change during the low-rate insulin infusion but significantly increased during high-rate insulin infusion (both P < .05). By showing a dose-dependent increasing influence of insulin on systolic BP and circulating catecholamine levels, the present study provides experimental evidence for the notion that hyperinsulinemia contributes to the development of hypertension.

Diabetes, glucose, insulin, and heart rate variability: the Atherosclerosis Risk in Communities (ARIC) study

OBJECTIVE

To describe the progression of autonomic impairment among individuals with diabetes and pre-diabetic metabolic impairments.

RESEARCH DESIGN AND METHODS

We investigated the consequence of diabetes and pre-diabetic metabolic impairments on the 9-year change in heart rate variability (HRV) in a population-based cohort of 6,245 individuals aged 45-64 years at baseline and cross-sectional associations among 9,940 individuals.

RESULTS

Diabetic subjects had a more rapid temporal decrease in HRV conditional on baseline HRV than nondiabetic subjects. Adjusted mean annual changes (95% CI) (ms/year) in the SD of all normal-to-normal R-R intervals were -0.65 (-0.69 to -0.61) for those with normal fasting glucose vs. -0.95 (-1.09 to -0.81) for diabetic subjects, in root mean square of successive differences in normal-to-normal R-R intervals -0.35 (-0.39 to -0.30) vs. -0.66 (-0.82 to -0.51), and in R-R interval 6.70 (6.37-7.04) vs. 3.89 (2.72-5.05). While we found cross-sectional associations between decreased HRV and diabetes and nondiabetic hyperinsulinemia and a weak inverse association with fasting glucose, neither impaired fasting glucose nor nondiabetic hyperinsulimenia was associated with a measurably more rapid decline in HRV than normal.

CONCLUSIONS

Cardiac autonomic impairment appears to be present at early stages of diabetic metabolic impairment, and progressive worsening of autonomic cardiac function over 9 years was observed in diabetic subjects. The degree to which pre-diabetic metabolic impairments in insulin and glucose metabolism contribute to decreases in cardiac autonomic function remains to be determined.

Insulin and lipid metabolism: new developments in drug therapy

Current treatments for non-insulin-dependent diabetes mellitus (NIDDM) remain far from ideal. The presence of both hyperinsulinaemia and resistance to insulin action in NIDDM challenges the rationale of treatments which primarily boost insulin secretion. Novel therapeutic strategies focus mainly on increasing peripheral sensitivity to endogenous insulin, an approach which has the potential not only to treat, but also to prevent NIDDM in high-risk individuals. The most promising new agents are the thiazolidinedione derivatives, in particular troglitazone. Thiazolidinediones are ligands for a specific subtype of the peroxisome proliferator activated receptor (PPAR), and decrease plasma glucose levels in both obesity and NIDDM, while at the same time reducing circulating insulin and free fatty acid levels. The current development status of these agents is reviewed, along with an assessment of their potential in the prevention and treatment of diverse pathophysiological states characterised by insulin resistance, including atherosclerosis and polycystic ovarian disease. Reference is made to the current status of other experimental agents including hydantoin derivatives, (3)-adrenoceptor agonists, and inhibitors of lipolysis.

Ambulatory blood pressure reduction after rosiglitazone treatment in patients with type 2 diabetes and hypertension correlates with insulin sensitivity increase

BACKGROUND

Within the metabolic syndrome, insulin resistance and compensatory hyperinsulinemia are associated with blood pressure (BP) elevation through various potential mechanisms. Thiazolidinediones are antihyperglycemic agents that decrease insulin resistance.

OBJECTIVE

To determine the effect of the thiazolidinedione rosiglitazone on BP and insulin resistance in patients with type 2 diabetes and hypertension.

METHODS

In 20 subjects (nine men and 11 women) with type 2 diabetes but with a poor glycemic control, and with poorly controlled or newly diagnosed hypertension, rosiglitazone 4 mg daily was added-on therapy for 26 weeks. At baseline and at the end of the treatment period patients underwent ambulatory blood pressure monitoring, a hyperinsulinemic euglycemic clamp, and blood tests for glucose, insulin, HbA1c, lipids, and routine laboratory parameters.

RESULTS

Insulin sensitivity estimated with the clamp significantly increased (Mbw/I index changed from 33.9 +/- 2.6 to 41.9 +/- 3.2 micromol/min per kg per nmol/l, P < 0.001) and the HOMA-IR index significantly decreased (6.34 +/- 0.39 versus 4.40 +/- 0.33, P < 0.001) during rosiglitazone treatment. Ambulatory BP presented small but significant reductions for the total 24-h period (135.3 +/- 1.8 versus 129.9 +/- 1.7 mmHg, P < 0.001 for systolic BP and 76.0 +/- 1.6 versus 71.9 +/- 1.6 mmHg, P < 0.001 for diastolic BP), daytime and night-time. The changes in systolic and diastolic BP correlated with the change in insulin sensitivity (r = -0.78, P < 0.01 and r = -0.68, P < 0.01, respectively). There were also significant reductions in fasting plasma glucose (9.39 +/- 0.41 versus 7.55 +/- 0.31 mmol/l, P < 0.001), insulin (94.0 +/- 0.41 versus 79.5 +/- 5.6 pmol/l, P < 0.01) and HbA1c (8.15 +/- 0.24 versus 7.24 +/- 0.19%, P < 0.001).

CONCLUSIONS

Treatment of type 2 diabetic hypertensive patients with rosiglitazone significantly increased insulin sensitivity and lowered ambulatory BP. These changes were strongly correlated. Thiazolidinediones may thus possess a BP-lowering effect beyond their antihyperglycemic properties.

Insulin infusion induces endothelin-1-dependent hypertension in rats

We previously showed that chronic insulin infusion induces insulin resistance, hyperendothelinemia, and hypertension in rats (C. C. Juan, V. S. Fang, C. F. Kwok, J. C. Perng, Y. C. Chou, and L. T. Ho. Metabolism 48: 465-471, 1999). Endothelin-1 (ET-1), a potent vasoconstrictor, is suggested to play an important role in maintaining vascular tone and regulating blood pressure, and insulin increases ET-1 production in vivo and in vitro. In the present study, BQ-610, a selective endothelin A receptor antagonist, was used to examine the role of ET-1 in insulin-induced hypertension in rats. BQ-610 (0.7 mg/ml; 0.5 ml/kg body wt) or normal saline was given intraperitoneally two times daily for 25 days to groups of rats infused with either saline or insulin (2 U/day via sc-implanted osmotic pumps), and changes in plasma levels of insulin, glucose, and ET-1 and the systolic blood pressure were measured over the experimental period, whereas changes in insulin sensitivity were examined at the end of the experimental period. Plasma insulin and ET-1 levels were measured by RIA, plasma glucose levels using a glucose analyzer, systolic blood pressure by the tail-cuff method, and insulin sensitivity by an oral glucose tolerance test. Our studies showed that insulin infusion caused sustained hyperinsulinemia in both saline- and BQ-610-injected rats over the infusion period. After pump implantation (2 wk), the systolic blood pressure was significantly higher in insulin-infused rats than in saline-infused rats in the saline-injected group (133 +/- 3.1 vs. 113 +/- 1.1 mmHg, P < 0.05) but not in the BQ-610-injected group (117 +/- 1.2 vs. 117 +/- 1.8 mmHg). Plasma ET-1 levels in both sets of insulin-infused rats were higher than in saline-infused controls (2.5 +/- 0.6 and 2.5 +/- 0.8 vs. 1.8 +/- 0.4 and 1.7 +/- 0.3 pmol/l, P < 0.05). Oral glucose tolerance tests showed that BQ-610 treatment did not prevent the insulin resistance caused by chronic insulin infusion. No significant changes were found in insulin sensitivity and blood pressure in saline-infused rats treated with BQ-610. In a separate experiment, insulin infusion induced the increase in arterial ET-1 content, hypertension, and subsequent plasma ET-1 elevation in rats. These results suggest that, in the insulin infusion rat model, ET-1 plays a mediating role in the development of hypertension, but not of insulin resistance.

Preventing heart failure in patients with diabetes

Diabetic cardiomyopathy is characterized by a prominent interstitial fibrosis. Postulated etiologies include microangiopathy, autonomic neuropathy, and metabolic factors. A common root of these pathologies is hyperglycemia or hyperinsulinemia, both of which are prominent in type 2 diabetes mellitus, which has the highest incidence of cardiovascular morbidity and mortality. The relative importance of each factor is a matter of debate; it is likely that both of these factors in addition to the concomitant risk factors seen in diabetics (dyslipidemias, hypertension, obesity, coagulation abnormalities) contribute to the spectrum of myocardial disease in diabetes. A discussion of these contributive pathologies and the hyperglycemia and hyperinsulinemia that underlie them is the subject of this review. Treatment methodologies to control the development of such pathology also are discussed.

The metabolic syndrome in overweight Hispanic youth and the role of insulin sensitivity

The prevalence of the metabolic syndrome is highest among Hispanic adults. However, studies exploring the metabolic syndrome in overweight Hispanic youth are lacking. Subjects were 126 overweight children (8-13 yr of age) with a family history for type 2 diabetes. The metabolic syndrome was defined as having at least three of the following: abdominal obesity, low high-density lipoprotein (HDL) cholesterol, hypertriglyceridemia, hypertension, and/or impaired glucose tolerance. Insulin sensitivity was determined by the frequently sampled iv glucose tolerance test and minimal modeling. The prevalence of abdominal obesity, low HDL cholesterol, hypertriglyceridemia, systolic and diastolic hypertension, and impaired glucose tolerance was 62, 67, 26, 22, 4, and 27%, respectively. The presence of zero, one, two, or three or more features of the metabolic syndrome was 9, 22, 38, and 30%, respectively. After controlling for body composition, insulin sensitivity was positively related to HDL cholesterol (P < 0.01) and negatively related to triglycerides (P < 0.001) and systolic (P < 0.01) and diastolic blood pressure (P < 0.05). Insulin sensitivity significantly decreased (P < 0.001) as the number of features of the metabolic syndrome increased. In conclusion, overweight Hispanic youth with a family history for type 2 diabetes are at increased risk for cardiovascular disease and type 2 diabetes, and this appears to be due to decreased insulin sensitivity. Improving insulin resistance may be crucial for the prevention of chronic disease in this at-risk population.

Daily exercise lowers blood pressure and reduces visceral adipose tissue areas in overweight Japanese men

OBJECTIVE

To investigate the link between a reduction in blood pressure (BP) and daily exercise.

DESIGN

Cross-sectional and longitudinal clinical intervention study with exercise education.

SUBJECTS

43 overweight Japanese men aged 32-59 years (BMI, 29.0+/-2.3 kg/m2) at baseline. Among the participants, a randomly selected 23 overweight men (BMI, 28.5+/-1.7) were further enrolled into the 10 months exercise program.

MEASUREMENTS

BP was measured every week and steps per day were also recorded every day throughout the observation period. Fat distribution was evaluated by visceral fat (V) and subcutaneous fat (S) areas measured with computed tomography (CT) scanning at umbilical level, at before, 5 months and after intervention. Anthropometric parameters were also measured at same point. Aerobic exercise level, muscle strength, flexibility and calorie intake and insulin resistance (HOMA index) were investigated at before and after the study.

RESULTS

In a cross sectional analysis, systolic BP (SBP) and diastolic BP (DBP) were significantly correlated with body composition. In a second longitudinal analysis, SBP was significantly reduced at 2 months and DBP was also reduced at 3 months, and almost maintained until the end of the observation period. Increasing daily walking was observed in 3 months and maintained until 10 months. Body composition, aerobic exercise level, muscle strength, flexibility and insulin resistance were significantly improved. There was positive correlation between DeltaDBP and Deltavisceral fat area (1-5, 5-10, 1-10 months). By stepwise multiple regression analysis, only Deltavisceral fat area was independently related to DeltaDBP at a significant level (1-10 months: DeltaDBP=-0.608+0.105Deltavisceral fat area, r2=0.227, P=0.0334).

CONCLUSION

The present study indicated daily exercise lowers BP and visceral fat area is the critical factor for BP change.

Effects of insulin on vascular responses to spinal cord stimulation and vasoactive agents in pithed rats

1. Effects of insulin (2-600 pmol kg(-1) min(-1), i.v.) on vascular responses to spinal cord (lower thoracic vertebra, Th 9-12) stimulation (SCS) and to i.v. injection of noradrenaline (NA, 125-500 ng kg-1), angiotensin II (Ang II, 40-200 pmol kg(-1), acetylcholine (ACh, 1 nmol kg(-1), calcitonin gene-related peptide (CGRP, 0.1 nmol kg(-1) and sodium nitroprusside (SNP, 5 microg kg-1) were examined in pithed rats. 2.In euglycemic pithed rats, low and medium doses of insulin dose-dependently potentiated vasopressor responses to SCS (2-8 Hz), NA, while higher doses of insulin had little effect on SCS- and NA-induced pressor responses. All doses of insulin significantly augmented pressor responses to Ang II. 3. In pithed rats with artificially increased blood pressure, SCS (2 and 4 Hz) induced a frequency-dependent depressor response, which was blocked by infusion of CGRP(8-37) (CGRP receptor antagonist, 60 nmol kg(-1) min(-1). 4. In euglycemic pithed rats, low-doses of insulin significantly attenuated depressor responses to SCS and CGRP, but medium and high doses of insulin remained unaffected. 5. All doses of insulin significantly inhibited depressor response to ACh, while SNP-induced depressor response was not significantly affected by any doses of insulin. 6. These results suggest that insulin at low and medium concentrations increases adrenergic vasoconstriction, which is partly associated with inhibition of CGRPergic nerve function and endothelium function. It is also suggested that lack of insulin effect at higher concentrations may result from acute desensitization of insulin action, possibly via insulin receptors.

Insulin preincubation effects on rat vessel contractile responses: role of the endothelium

The effect of contractions elicited with ET1 and AVP after preincubating rat aortic and tail artery rings with a hyperinsulinemic dose (3 nM) of insulin were studied. Insulin preincubation (120 min), in the presence of 0.1 mM L-NAME, depressed contraction of aortic rings to 0.01 microM ET1 (132 +/- 6 vs. 161 +/- 9 mg/mm2 in control, n = 25; p < 0.05) and to 1 microM AVP (84 +/- 7 vs. 110 +/- 9 mg/mm2 in control, n = 16; p < 0.05), but did not modify 45Ca influx to the cell. Insulin-induced relaxation was inhibited by indomethacin 10 microM, an antagonist of prostaglandin synthesis, and also by blockade of insulin receptors with 30 microM genistein. A short insulin preincubation (15 min) did not modify ET1 contractions. In rat tail artery, insulin preincubation (120 min) increased the force developed by ET1 (847 +/- 45 vs. 596 +/- 99 mgF/mgW in controls, n = 14) by stimulating TXA2 release and/or actions. In summary, the present results suggest that endothelial factors are involved in both the vasoconstrictor and vasodilator effects of insulin on rat vessels.

The role of the sympathetic nervous system in linking obesity with hypertension in white versus black Americans

Several previous studies confirmed that obesity is a major risk factor for the development of cardiovascular diseases, including hypertension. A large number of clinical studies considered the role of the sympathetic nervous system in linking obesity with hypertension, and there is substantial evidence that human obesity is characterized by defects in sympathetic cardiovascular control. The association of obesity with hypertension has been well documented in most racial, ethnic, and socioeconomic groups. Ethnicity may be an important factor to consider since sympathetic nervous system activity, and the propensity for obesity and hypertension, all differ substantially among different populations. Obesity is actually accompanied by increased sympathetic nerve discharge to skeletal muscles, a main site for energy expenditure. Adiposity-related sympathetic overactivity is a compensatory mechanism to burn fat and decrease weight gain, but at the cost of increased sympathetic discharge to the peripheral vasculature, which could predispose to hypertension. Thus, sympathetic nervous system activity is important in the development and maintenance of obesity-related hypertension in different racial and ethnic populations, including white and black Americans.

Insulin Resistance and Hypertension: Seven-Year Follow-Up Study in Middle-Aged Japanese Men (the KEIO Study)

Only a few longitudinal studies in Asians have shown a close association between hyperinsulinemia and the incidence of hypertension. In the present study, we used the insulin resistance index, HOMA-IR [fasting plasma glucose (FPG) (mmol/l) X insulin (microUl/ml) / 22.5], and tried to elucidate longitudinally the relationship among insulin resistance, blood pressure, body mass index (BMI), FPG, and lipid profile in middle-aged Japanese men. Three hundred and ten male non-hypertensive subjects aged 30 to 58 years in 1993 (44.5 +/- 7.8 (SD) years; BMI, 22.6 +/- 2.5 kg/m2) were divided into three groups according to HOMA-IR (A: lowest; B: middle; and C: highest). Their BMI, systolic blood pressure (SBP), diastolic blood pressure (DBP), heart rate, FPG and lipid profile were followed up for 7 years. The percentage of high normal blood pressure in 1993 and 2000 did not differ among the three groups. However, in 2000 hypertensive subjects made up 11.7% of group A (12/103), 15.4% of group B (16/104), and 29.1% of group C (30/103) (chi2 = 11.50, p = 0.003). SBP, DBP, and many other metabolic parameters in 2000 were significantly higher in group C than in the other groups. Furthermore, both SBP and DBP in 2000 were positively correlated with HOMA-IR in 1993 (r = 0.17 and p < 0.01 for both). The correlation between HOMA-IR in 1993 and DBP in 2000 was significant, even after adjustment for age and BMI in 1993. These findings suggest an important role of insulin resistance in predicting the future incidence of hypertension in middle-aged Japanese men.

Insulin sensitivity and blood pressure in black and white children

Although insulin sensitivity is correlated with high blood pressure in adults, it is unclear whether such a relationship exists in children across ethnic groups. Therefore, the aims of the study were to establish (1) if body composition and insulin sensitivity were related to blood pressure in children, and (2) if any differences in blood pressure between white and black children were explained by body composition and/or insulin sensitivity. Insulin sensitivity and the acute insulin response were established by the minimal model and body composition by dual-energy X-ray absorptiometry. Blood pressure was recorded in the supine position. Body composition, fasting insulin (P<0.01), and the acute insulin response (P<0.05) were positively related to systolic blood pressure but not to diastolic blood pressure, and insulin sensitivity (P<0.001) was negatively related to systolic blood pressure but not to diastolic blood pressure. Insulin sensitivity was negatively associated with systolic and diastolic blood pressure after adjustment for body composition (P<0.01). Black children had higher systolic (110+/-9.2 versus 105+/-8.5 mm Hg, P=0.01) and diastolic (59+/-7.0 versus 54+/-8.0 mm Hg, P<0.01) blood pressure than did white children. The ethnic difference in blood pressure was not explained by body composition, fasting insulin, acute insulin response, or insulin sensitivity. In conclusion, the relationship between insulin sensitivity and systolic blood pressure is evident early in life. Black ethnicity and low insulin sensitivity contribute independently to higher blood pressure in children.

Quinapril treatment restores the vasodilator action of insulin in fructose-hypertensive rats

1. Angiotensin-converting enzyme (ACE) inhibitors have been shown to improve insulin-resistance both experimentally and clinically. We therefore investigated the effects of quinapril, which has high tissue specificity for ACE, regarding the contribution of insulin to vascular contractions, as well as insulin sensitivity in a dietary rat model of insulin resistance. 2. Male Sprague-Dawley rats were divided into three groups: (i) rats fed normal chow (normal diet group); (ii) rats fed fructose-rich chow containing 40% fructose and 7% lard (fructose diet group); and (iii) rats fed fructose-rich chow plus quinapril (10 mg/kg per day; quinapril-treated group). 3. After 2 weeks, we evaluated systolic blood pressure, insulin sensitivity as assessed by steady state plasma glucose (SSPG) levels, response of aortic rings to phenylephrine (10-9 to 10-6 mol/L) in the presence or absence of insulin and the response of aortic rings to acetylcholine. 4. Feeding rats fructose-rich chow resulted in an elevation of blood pressure (P < 0.01) and SSPG levels (P < 0.01). Quinapril treatment significantly prevented increases in both blood pressure and SSPG, with a return to the levels seen in the normal diet group. 5. In the absence of insulin, the maximal contractile response to phenylephrine did not differ between the three groups. However, in the presence of insulin (100 mU/mL), the contractile response to phenylephrine (10-6 mol/L) was reduced by 22.8 +/- 1.2% in the normal diet group, although no insulin effects were observed in the fructose diet group (P < 0.01). Quinapril restored the inhibitory effect of insulin on phenylephrine-induced contractions. 6. In addition, the reduction in relaxation induced by acetylcholine in the fructose diet group was significantly reversed by quinapril treatment. 7. It is concluded that the fructose diet impairs the vasodilator effects of insulin as well as acetylcholine-induced relaxation in rat thoracic aortas. Quinapril prevented deterioration in the responses of the aortic rings, suggesting that ACE inhibitors may be useful for treating vascular insulin resistance.

Cardiovascular and sympathetic effects of leptin

Several studies have shown the association between obesity and hypertension. The pathophysiologic mechanisms of obesity-related hypertension remain unknown. Clinical and experimental studies have shown that obesity is associated with enhanced sympathetic nervous activity. Thus, sympathetic nerve activation seems to play a major role in obesity-associated hypertension. However, the factors responsible for this sympathoactivation have not been identified. Leptin is an adipocyte-derived hormone that promotes weight loss by reducing appetite and food intake and by increasing energy expenditure through sympathetic stimulation to brown adipose tissue. Leptin also produces sympathoactivation to kidneys, hindlimb, and adrenal glands, indicating that the obesity-associated increase in sympathetic nerve activity could be due in part to these sympathetic effects of leptin. However, obesity is associated with leptin resistance, since high circulating levels of leptin were observed in obese subjects. Recent evidences indicate that this leptin resistance could be selective with preservation of sympathetic effects despite the loss of metabolic action of leptin. This suggests divergent central pathways underlying metabolic and sympathetic effects of leptin. Several neuropeptides have emerged as potent candidate mediators of leptin action in the central nervous system, including the melanocortin system, neuropeptide Y, and cortico-trophin releasing factor. A detailed understanding of the multitude and complexity of integrated neuronal circuits and neuropeptide-containing pathways in leptin action will help in understanding the pathogenesis of obesity and related disorders.

No role of calcium- and ATP-dependent potassium channels in insulin-induced vasodilation in humans in vivo

The mechanism of insulin-induced vasodilation has not been completely clarified, but could be important in future treatment strategies of insulin resistance. Recently, a role for calcium-dependent and ATP-dependent potassium (K(Ca) and K(ATP)) channels in insulin-induced vasodilation has been demonstrated in in vitro studies. A role for these channels has never been confirmed in humans in vivo. Therefore, we investigated the role of these channels in insulin-induced vasodilation in humans in vivo. A hyperinsulinemic euglycemic clamp was combined with intra-arterial infusion of placebo, tetraethylammonium (blocker of K(Ca) channels) or glibenclamide (blocker of K(ATP) channels) in three groups of 12 healthy volunteers. Bilateral forearm blood flow was measured with venous occlusion plethysmography. Systemic hyperinsulinemia induced a 20+/-9% vasodilation (p=0.001). Neither tetraethylammonium nor glibenclamide reduced this vasodilation as compared to placebo. According to the results of the present study, insulin-induced vasodilation seems not to be mediated by the opening of K(Ca) and K(ATP) channels in humans in vivo.

The effects of valsartan on insulin sensitivity in patients with primary hypertension

Insulin resistance is an important risk factor of cardiovascular disease. This study was performed to determine the effects of valsartan on insulin sensitivity in patients with primary hypertension. In this study, non-obese subjects with primary hypertension and a reference group of healthy subjects matched by age, sex and body mass index were evaluated; patients with any other causes of peripheral insulin resistance and hyperlipidaemia were excluded. The effect of valsartan on insulin resistance, assessed by homeostasis model assessment (HOMA-IR), fasting serum insulin levels, determined by radioimmunoassay, and fasting blood glucose concentrations, measured by the glucose oxidase method, were evaluated. All obtained data were evaluated by Pearson correlation analysis. Before valsartan treatment, the fasting serum insulin levels were significantly elevated in the 20 hypertensive patients with primary hypertension compared with the 20 subjects in the reference group (19.6 +/- 7.1 versus 8.7 +/- 1.9 microIU/ml). The fasting serum insulin levels correlated with HOMA-IR. Correlation analysis also showed a significant relationship between HOMA-IR and both systolic and diastolic blood pressures (r = 0.71 and r = 0.77, respectively). In our study, we showed that patients with primary hypertension have a decreased insulin sensitivity that was reflected in high serum fasting insulin levels. Anti-hypertensive treatment with valsartan increases insulin sensitivity.