Effects of insulin on the cardiac autonomic nervous system in insulin-resistant states

Metabolic and sympathovagal effects of bolus insulin glulisine versus basal insulin glargine therapy in people with type 2 diabetes: A randomized controlled study

AIMS/INTRODUCTION

This study compares the effects of two different insulin regimens - basal versus bolus insulin - on metabolic and cardiovascular autonomic function in Japanese participants with type 2 diabetes.

MATERIALS AND METHODS

Participants were randomly assigned to groups for therapy with insulin glulisine (IGlu) or insulin glargine (IGla). The primary efficacy end-point was glycemic variability, including M-values, mean of glucose levels, and a blood glucose profile of seven time points before and after the intervention. The secondary end-points included pleiotropic effects, including endothelial and cardiac autonomic nerve functions.

RESULTS

Blood glucose levels at all time points significantly decreased in both groups. Post-lunch, post-dinner, and bedtime blood glucose levels were significantly lower in the IGlu group than in the IGla group. Nadir fasting blood glucose levels at the end-point were significantly lower in the IGla group than in the IGlu group. The M-value and mean blood glucose levels were significantly decreased from baseline in both groups, although the former was significantly lower in the IGlu group than in the IGla group. IGla, but not IGlu, was found to elevate 24-h parasympathetic tone, especially during night-time, and it decreased 24-h sympathetic nerve activity, especially at dawn.

CONCLUSIONS

Both IGlu and IGla regimens reduced glucose variability, with IGlu bringing a greater reduction in M-value. IGla, but not IGlu, increased parasympathetic tone during night-time and decreased sympathetic nerve activity at dawn. These findings shed light on the previously unrecognized role of night-time basal insulin supplementation on sympathovagal activity in type 2 diabetes patients.

Metformin may adversely affect orthostatic blood pressure recovery in patients with type 2 diabetes: substudy from the placebo-controlled Copenhagen Insulin and Metformin Therapy (CIMT) trial

Background

Metformin has been shown to have both neuroprotective and neurodegenerative effects. The aim of this study was to investigate the effect of metformin in combination with insulin on cardiovascular autonomic neuropathy (CAN) and distal peripheral neuropathy (DPN) in individuals with type 2 diabetes (T2DM).

Methods

The study is a sub-study of the CIMT trial, a randomized placebo-controlled trial with a 2 × 3 factorial design, where 412 patients with T2DM were randomized to 18 months of metformin or placebo in addition to open-labelled insulin. Outcomes were measures of CAN: Changes in heart rate response to deep breathing (beat-to-beat), orthostatic blood pressure (OBP) and heart rate and vibration detection threshold (VDT) as a marker DPN. Serum levels of vitamin B12 and methyl malonic acid (MMA) were analysed.

Results

After 18 months early drop in OBP (30 s after standing) was increased in the metformin group compared to placebo: systolic blood pressure drop increased by 3.4 mmHg (95% CI 0.6; 6.2, p = 0.02) and diastolic blood pressure drop increased by 1.3 mmHg (95% CI 0.3; 2.6, p = 0.045) compared to placebo. Beat-to-beat variation decreased in the metformin group by 1.1 beats per minute (95% CI − 2.4; 0.2, p = 0.10). Metformin treatment did not affect VDT group difference − 0.33 V (95% CI − 1.99; 1.33, p = 0.39) or other outcomes. Changes in B12, MMA and HbA_1c did not confound the associations.

Conclusions

Eighteen months of metformin treatment in combination with insulin compared with insulin alone increased early drop in OBP indicating an adverse effect of metformin on CAN independent of vitamin B12, MMA HbA_1c.

Trial registration The protocol was approved by the Regional Committee on Biomedical Research Ethics (H–D-2007-112), the Danish Medicines Agency and registered with ClinicalTrials.gov (NCT00657943).

Insulin resistance and reduced cardiac autonomic function in older adults: the Atherosclerosis Risk in Communities study

Background

Prior studies have shown insulin resistance is associated with reduced cardiac autonomic function measured at rest, but few studies have determined whether insulin resistance is associated with reduced cardiac autonomic function measured during daily activities.

Methods

We examined older adults without diabetes with 48-h ambulatory electrocardiography (n = 759) in an ancillary study of the Atherosclerosis Risk in Communities Study. Insulin resistance, the exposure, was defined by quartiles for three indexes: 1) the homeostatic model assessment of insulin resistance (HOMA-IR), 2) the triglyceride and glucose index (TyG), and 3) the triglyceride to high-density lipoprotein cholesterol ratio (TG/HDL-C). Low heart rate variability, the outcome, was defined by <25th percentile for four measures: 1) standard deviation of normal-to-normal R-R intervals (SDNN), a measure of total variability; 2) root mean square of successive differences in normal-to-normal R-R intervals (RMSSD), a measure of vagal activity; 3) low frequency spectral component (LF), a measure of sympathetic and vagal activity; and 4) high frequency spectral component (HF), a measure of vagal activity. Logistic regression was used to estimate odds ratios (OR) and 95% confidence intervals weighted for sampling/non-response, adjusted for age at ancillary visit, sex, and race/study-site. Insulin resistance quartiles 4, 3, and 2 were compared to quartile 1; high indexes refer to quartile 4 versus quartile 1.

Results

The average age was 78 years, 66% (n = 497) were women, and 58% (n = 438) were African American. Estimates of association were not robust at all levels of HOMA-IR, TyG, and TG/HDL-C, but suggest that high indexes were associated consistently with indicators of vagal activity. High HOMA-IR, high TyG, and high TG/HDL-C were consistently associated with low RMSSD (OR: 1.68 (1.00, 2.81), OR: 2.03 (1.21, 3.39), and OR: 1.73 (1.01, 2.91), respectively). High HOMA-IR, high TyG, and high TG/HDL-C were consistently associated with low HF (OR: 1.90 (1.14, 3.18), OR: 1.98 (1.21, 3.25), and OR: 1.76 (1.07, 2.90), respectively).

Conclusions

In older adults without diabetes, insulin resistance was associated with reduced cardiac autonomic function – specifically and consistently for indicators of vagal activity – measured during daily activities. Primary prevention of insulin resistance may reduce the related risk of cardiac autonomic dysfunction.

Differential associations of lower cardiac vagal tone with insulin resistance and insulin secretion in recently diagnosed type 1 and type 2 diabetes

OBJECTIVE

It is unclear to which extent altered insulin sensitivity/secretion contribute to the development of diabetic cardiovascular autonomic neuropathy (CAN) characterized by diminished heart rate variability (HRV). We hypothesised that lower HRV is differentially associated with measures of insulin resistance and insulin secretion in recent-onset type 1 and type 2 diabetes.

MATERIALS/METHODS

This cross-sectional study included participants from the German Diabetes Study with type 1 (n=275) or type 2 diabetes (n=450) with known diabetes duration ≤1year and glucose-tolerant controls (n=81). Four time domain and frequency domain HRV measures each, reflecting vagal and/or sympathetic modulation were determined over 3h during a hyperinsulinaemic-euglycaemic clamp. Insulin sensitivity was calculated as the M-value, while insulin secretion was determined by glucagon-stimulated incremental C-peptide (ΔC-peptide).

RESULTS

After adjustment for sex, age, BMI, smoking, and HbA1c, both M-value and ΔC-peptide were lower in the diabetes groups compared to controls (P<0.05). In multiple linear regression analyses after Bonferroni correction, vagus-mediated HRV indices were positively associated with M-value in both diabetes types (P<0.05) and inversely associated with ΔC-peptide only in participants with type 1 diabetes (P<0.05). In type 2 diabetes, the low-frequency/high-frequency (LF/HF) power as an indicator of sympathovagal balance was weakly inversely associated with M-value.

CONCLUSIONS

Insulin resistance may contribute to the development of early cardiovagal suppression rather than sympathetic predominance in both diabetes types, while in type 1 diabetes a lower glucagon-stimulated insulin secretion is linked to a possibly compensatory higher parasympathetic tone. Whether interventions aimed at reducing insulin resistance could also reduce the risk of CAN remains to be established.

Feeling the pressure: (patho) physiological mechanisms of weight gain and weight loss in humans

Obesity is an ongoing global epidemic and has adverse consequences for cardiovascular health. Obesity is often associated with hypertension, which is, itself, a common condition and an important cause of morbidity and mortality worldwide. Although animal models of obesity have provided extensive data on the links between obesity and hypertension, a greater understanding of the pathways linking obesity and hypertension in humans is likely to assist translation of animal data, and may, itself, identify important treatment strategies. Ultimately, this could have a substantial impact on human health, both at an individual and population level. The current review will focus specifically on studies of experimental weight gain and weight loss in humans and the following key areas, which are strongly related to blood pressure: cardiovascular function, autonomic nervous system function, metabolic function and the impact of cardiorespiratory fitness.

Differential Patterns and Determinants of Cardiac Autonomic Nerve Dysfunction during Endotoxemia and Oral Fat Load in Humans

The autonomic nervous system (ANS) plays an important role in regulating the metabolic homeostasis and controlling immune function. ANS alterations can be detected by reduced heart rate variability (HRV) in conditions like diabetes and sepsis. We determined the effects of experimental conditions mimicking inflammation and hyperlipidemia on HRV and heart rate (HR) in relation to the immune, metabolic, and hormonal responses resulting from these interventions. Sixteen lean healthy subjects received intravenous (i.v.) low-dose endotoxin (lipopolysaccharide [LPS]), i.v. fat, oral fat, and i.v. glycerol (control) for 6 hours, during which immune, metabolic, hormonal, and five HRV parameters (pNN50, RMSSD, low-frequency (LF) and high-frequency (HF) power, and LF/HF ratio) were monitored and energy metabolism and insulin sensitivity (M-value) were assessed. LPS infusion induced an increase (AUC) in HR and LF/HF ratio and decline in pNN50 and RMSSD, while oral fat resulted in elevated HR and a transient (hours 1-2) decrease in pNN50, RMSSD, and HF power. During LPS infusion, ΔIL-1ra levels and ΔIL-1ra and ΔIL-1ß gene expression correlated positively with ΔLF/HF ratio and inversely with ΔRMSSD. During oral fat intake, ΔGLP-1 tended to correlate positively with ΔHR and inversely with ΔpNN50 and ΔRMSSD. Following LPS infusion, lipid oxidation correlated positively with HR and inversely with pNN50 and RMSSD, whereas HRV was not related to M-value. In conclusion, suppression of vagal tone and sympathetic predominance during endotoxemia are linked to anti-inflammatory processes and lipid oxidation but not to insulin resistance, while weaker HRV changes in relation to the GLP-1 response are noted during oral fat load.

Associations between insulin and heart rate variability in police officers

OBJECTIVE

Low heart rate variability (HRV) has been linked to cardiovascular disease. Our objective was to examine the cross-sectional association between insulin and HRV.

METHODS

Insulin levels were measured in 355 nondiabetic officers from the BCOPS study, following a 12 h fast. HRV was performed according to methods published by the task force of the European Society of Cardiology and the North American Society of Pacing Electrophysiology for measurement and analysis of HRV. Mean values of high (HF) and low frequency (LF) HRV were compared across tertiles of insulin using ANOVA and ANCOVA; p-values were obtained from linear regression models.

RESULTS

Higher mean levels of insulin were significantly associated with lower (i.e., worse) mean levels of HRV before and after risk-factor adjustment. The results for HF HRV (ms(2)) were as follows: 1st insulin (µU/ml) tertile (156.3; 95% confidence interval (CI) = 128.6-189.9); 2nd tertile (154.3; 95% CI = 124.3-191.5); 3rd tertile (127.9; 95% CI = 105.0-155.8), p for trend = 0.017. Results with LF HRV were similar to HF HRV. Insulin was also inversely and significantly associated with HRV among officers with BMI ≥ 25 kg/m(2), with ≥ 25.5% body fat, and among those who reported low (<median) physical activity scores.

CONCLUSIONS

In this cohort, insulin levels were inversely and significantly associated with both HF and LF HRV, especially among those with higher levels of obesity and lower levels of physical activity, suggesting associations with autonomic nervous system function. Prospective studies of this association in other populations are warranted.

Insulin- and glucagon-like peptide-1-induced changes in heart rate and vagosympathetic activity: why they matter

Heart rate (HR) predicts cardiovascular morbidity and mortality in individuals either with or without diabetes. In type 2 diabetic patients, cardiac autonomic neuropathy is a risk marker for cardiac morbidity and mortality. A major pathogenic potential may be attributed to vagal depression and sympathetic predominance. In this issue of Diabetologia, Berkelaar et al (DOI: 10.1007/s00125-013-2848-6 ) examined the effects of euglycaemic, and hyperglycaemic clamp with the addition of glucagon-like-peptide-1 (GLP-1) and arginine, on cardiac vagal control in a large number of healthy subjects. After adjustments for age, BMI and insulin sensitivity, insulin associations with HR remained partially intact while those with vagal control disappeared. This suggested that BMI and insulin sensitivity, but not insulin levels, were the main drivers of cardiac vagal control. GLP-1 infusion during hyperglycaemia increased HR and BP and produced a statistically non-significant decrease in measures of cardiac vagal control compared with values before any manipulation of insulin levels. This commentary summarises how, and to what extent, insulin and GLP-1 affect autonomic nervous system activity, HR and BP. More information is needed on the mechanisms through which acute administration of, and long-term treatment with, GLP-1 may affect haemodynamics and autonomic activity in diabetic and obese patients, since this may influence cardiovascular outcomes.

Blood Pressure Control at Rest and during Exercise in Obese Children and Adults

The hemodynamic responses to exercise have been studied to a great extent over the past decades, and an exaggerated blood pressure response during an acute exercise bout has been considered as an indicator of cardiovascular risk. Obesity is a major factor influencing the blood pressure response to exercise since evidence indicates that the arterial pressure response to exercise is exacerbated in obese compared with lean adults. Signs of augmented responses (such as an exaggerated blood pressure response) to physical exertion appear early in life (from the prepubertal years) in obese individuals. Understanding the mechanisms that drive the altered hemodynamic responses during exercise in obese individuals and prevent the progression to hypertension is vitally important. This paper focuses on the evidence linking obesity with alterations of the autonomic nervous system and discusses the potential mechanisms and consequences of the altered sympathetic nervous system behavior in obese individuals at rest and during exercise. Furthermore, this paper presents the alterations in the reflex regulatory mechanisms ("exercise pressor reflex" and baroreflex) in obese children and adults and addresses the effects of training on obesity-related disturbances.

Resting heart rate and metabolic syndrome in patients with diabetes and coronary artery disease in bypass angioplasty revascularization investigation 2 diabetes (BARI 2D) trial

The relation between the metabolic syndrome (MetS) and resting heart rate (rHR) in patients with diabetes and coronary artery disease is unknown. The authors examined the cross-sectional association at baseline between components of the MetS and rHR and between rHR and left ventricular ejection fraction in the population from the Bypass Angioplasty Revascularization Investigation 2 Diabetes (BARI 2D) randomized clinical trial. The mean rHR in the MetS group was significantly higher than in those without (68.4+/-12.3 vs 65.6+/-11.8 beats per min, P=.0017). The rHR was higher (P<.001 for trend) with increasing number of components for MetS. Linear regression analyses demonstrated that as compared to individuals without MetS, rHR was significantly higher in participants with MetS (regression coefficient, 2.9; P=.0015). In patients with type 2 diabetes and coronary artery disease, the presence of higher rHR is associated with increasing number of criteria of MetS and the presence of ventricular dysfunction.

Exercise training improves cardiovascular autonomic modulation in response to glucose ingestion in obese adults with and without type 2 diabetes mellitus

This study examined the effect of aerobic exercise training on vagal and sympathetic influences on the modulations of heart rate and systolic blood pressure in response to an oral glucose load in obese individuals with and without type 2 diabetes mellitus (T2D). Beat-to-beat arterial pressure and continuous electrocardiogram were measured after a 12-hour overnight fast and in response to glucose ingestion (75 g dextrose) in obese subjects with (T2D group, n = 23) and without (OB group, n = 36) T2D before and after 16 weeks of aerobic exercise training at moderate intensity. Autonomic modulation was assessed using spectral analysis of systolic blood pressure variability (BPV), heart rate variability (HRV), and analysis of baroreflex sensitivity (BRS). Glucose ingestion significantly increased low-frequency (LF(SBP)), low-frequency HRV (LF(RRI)), and the ratio of low- to high-frequency components of HRV (LF(RRI)/HF(RRI)), and decreased the high-frequency power (HF(RRI)) (P < .05). Exercise training increased LF(RRI) and LF(RRI)/HF(RRI) responses, and reduced HF(RRI) and LF(SBP) to glucose ingestion in both groups (P < .05), but increased fasted BRS in the OB group only (P < .05); glucose intake had no effect on BRS (P > .05). In conclusion, a 16-week exercise training program improved cardiac autonomic modulation in response to an oral glucose load in obese adults, independently of diabetes status, and in the absence of remarkable changes in body weight, body composition, fitness level, and glycemic control.

Impact of body fat mass extent on cardiac autonomic alterations in women

BACKGROUND

Obesity has been associated with significant abnormalities of the cardiac autonomic regulation. However, the precise impact of increasing body weight on cardiac autonomic function and the metabolic and hormonal contributors to these changes are presently unclear. The aim of our study was to explore in subjects with increasing values of body mass index (BMI) the alterations of cardiac autonomic function and to establish the potential role of various metabolic and hormonal contributors to these alterations.

MATERIALS AND METHODS

We investigated time and frequency domain heart rate variability (HRV) parameters taken from 24-h Holter recordings, and several anthropometric, metabolic and hormonal parameters (plasma glucose, insulin, triglycerides, free fatty acids, leptin and adiponectin) in 68 normoglycaemic and normotensive women (mean age of 40 +/- 3 years), subdivided according to their BMI into 15 normal body weight (controls), 15 overweight, 18 obese and 20 morbidly obese.

RESULTS

Heart rate was increased and HRV was decreased in the morbidly obese group as compared with controls. In overall population, a negative association linked body fat mass (FM) to HRV indices. None of the metabolic and hormonal parameters were significantly related to the HRV indices, after they were adjusted for the body FM.

CONCLUSIONS

Morbidly obese, normoglycaemic and normotensive young women have increased HR and low HRV, indicating an abnormal cardiac autonomic function and representing a risk factor for adverse cardiovascular events. A decrease of HRV parameters is associated with a progressive increase of body FM. Other metabolic and hormonal factors, characterising obesity, do not show an independent influence on these HRV alterations.

Sympathetic System Activity in Obesity and Metabolic Syndrome

Obesity is a very common disease worldwide, resulting from a disturbance in the energy balance. The metabolic syndrome is also a cluster of abnormalities with basic characteristics being insulin resistance and visceral obesity. The major concerns of obesity and metabolic syndrome are the comorbidities, such as type 2 diabetes, cardiovascular disease, stroke, and certain types of cancers. Sympathetic nervous system (SNS) activity is associated with both energy balance and metabolic syndrome. Sympathomimetic medications decrease food intake, increase resting metabolic rate (RMR), and thermogenic responses, whereas blockage of the SNS exerts opposite effects. The contribution of the SNS to the daily energy expenditure, however, is small ( approximately 5%) in normal subjects consuming a weight maintenance diet. Fasting suppresses, whereas meal ingestion induces SNS activity. Most of the data agree that obesity is characterized by SNS predominance in the basal state and reduced SNS responsiveness after various sympathetic stimuli. Weight loss reduces SNS overactivity in obesity. Metabolic syndrome is characterized by enhanced SNS activity. Most of the indices used for the assessment of its activity are better associated with visceral fat than with total fat mass. Visceral fat is prone to lipolysis: this effect is mediated by catecholamine action on the sensitive beta(3)-adrenoceptors found in the intraabdominal fat. In addition, central fat distribution is associated with disturbances in the hypothalamo-pituitary-adrenal axis, suggesting that a disturbed axis may be implicated in the development of the metabolic syndrome. Furthermore, SNS activity induces a proinflammatory state by IL-6 production, which in turn results in an acute phase response. The increased levels of inflammatory markers seen in the metabolic syndrome may be elicited, at least in part, by SNS overactivity. Intervention studies showed that the disturbances of the autonomic nervous system seen in the metabolic syndrome are reversible.

Influence of Autonomic Nervous Dysfunction Characterizing Effect of Diabetes Mellitus on Heart Rate Response and Exercise Capacity in Patients Undergoing Cardiac Rehabilitation for Acute Myocardial Infarction

BACKGROUND

The aim of this study was to clarify the influence of sympathetic and parasympathetic nerve (SN and PN) dysfunction on the heart rate (HR) response to exercise and the exercise capacity of patients with acute myocardial infarction (AMI) and diabetes mellitus (DM).

METHODS AND RESULTS

Fifty-two male patients who underwent cardiopulmonary exercise testing (CPX) 1 month after onset of AMI were divided into 2 groups: (DM (+) group, n=20; DM (-) group, n=32). HR, peak oxygen uptake (VO2peak), and plasma norepinephrine (NE) levels were measured during CPX. The high-frequency power (HF) was analyzed by HR variability. The DeltaHR/logDeltaNE obtained from changes of HR and NE from rest to peak exercise and HR change from baseline to the minimum HF (DeltaHRHF) were calculated as parameters of HR response derived from SN and PN activities, respectively. DeltaHR, VO2peak, DeltaHR/logDeltaNE, and DeltaHRHF were significantly lower in the DM (+) group than in the DM (-) group, and both of them showed positive correlations with VO2peak.

CONCLUSION

An inadequate HR response to exercise is a major factor causing a decline of exercise capacity, which is derived from both of SN and PN dysfunction, in AMI patients with DM.

Insulin downregulates M(2)-muscarinic receptors in adult rat atrial cardiomyocytes: a link between obesity and cardiovascular complications

OBJECTIVE

To determine whether decreased cardiac parasympathetic activity observed in obesity is due to insulin-induced alterations in cardiac M(2)-muscarinic receptors and/or adenylyl cyclase activity.

DESIGN AND METHODS

After incubation with increasing concentrations of insulin, adult rat atrial cardiomyocytes were assayed for M(2)-muscarinic receptor binding density and affinity, and for M(2)R mRNA expression using RT-PCR analysis. Forskolin-stimulated adenylyl cyclase activity and its inhibition by carbachol were also assayed, as was endothelial nitric oxide synthase mRNA expression. The effects of insulin on M(2)-muscarinic receptor density and mRNA expression levels were analyzed using the insulin signaling inhibitors rapamycin, wortmanin and PD 098059.

RESULTS

Insulin induces a concentration- and time-dependent decrease in expression of the M(2)R mRNA, and in [(3)H]N-methylscopolamine binding by the receptor. These effects on the M(2)R mRNA levels and on [(3)H]N-methylscopolamine binding were prevented by PD 98059, but not by wortmanin or rapamycin. Basal and forskolin-induced cAMP production did not differ, but the inhibition of forskolin-simulated enzyme activity by carbachol was blunted by insulin. No change in the mRNA levels for endothelial nitric oxide synthase was observed.

CONCLUSION

In rat atrial cardiomyocytes, insulin markedly alters both the M(2)-muscarinic receptor density, and its mRNA expression through transcriptional regulation and adenylyl cyclase activity. These data suggest that the obesity-associated decrease in cardiac parasympathetic tone may be related to hyperinsulinemia, which could directly contribute to cardiovascular morbidity in obese patients.

Cardiac autonomic activity and Type II diabetes mellitus

CAN (cardiac autonomic neuropathy) is a common complication of diabetes. Meta-analyses of published data demonstrate that reduced cardiovascular autonomic function, as measured by heart rate variability, is strongly associated with an increased risk of silent myocardial ischaemia and mortality. A major problem in ischaemia-induced impairment of vascular performance in the diabetic heart is unrecognized cardiac sympathetic dysfunction. Determining the presence of CAN is based on a battery of autonomic function tests and techniques such as SPECT (single-photon emission computed tomography) and PET (positron emission tomography). Nevertheless, spectral analysis of heart rate variability seems to remain the primary technique in evaluating CAN, due to its low cost, easy use and good intra-individual reproducibility.

Disparity of autonomic control in type 2 diabetes mellitus

AIMS/HYPOTHESIS

Acute insulinaemia activates the sympathetic drive in a nonuniform manner. The extent and nature of such activation in type 2 diabetic patients who do not have neuropathy have not yet been addressed despite evidence relating sympathetic activation to cardiovascular risk. We planned to determine the magnitude and extent of the sympathetic drive and its reflex responses in patients with type 2 diabetes and fasting hyperinsulinaemia.

METHODS

We measured resting muscle sympathetic nerve activity (MSNA) as the mean frequency of multi-unit bursts and single unit muscle sympathetic nerve activity (s-MSNA) in 17 overweight patients with type 2 diabetes and two matched normal control groups comprising 17 overweight and 16 normal-weight subjects. We also tested the MSNA and s-MSNA responses to cold pressor and isometric hand-grip tests, along with the effect of sympatho-vagal balance on heart period variability.

RESULTS

Both MSNA and s-MSNA in the group with type 2 diabetes (66+/-3.5 bursts/100 beats and 78+/-4.5 impulses/100 beats) were greater (at least p<0.0001) than in the overweight control group (42+/-2.6 bursts/100 beats and 48+/-3.4 impulses/100 beats) and normal-weight control group (43+/-6.2 bursts/100 beats and 51+/-7.1 impulses/100 beats), though the three groups had similar reflex responses, baroreflex sensitivity and sympatho-vagal balance controlling the heart period.

CONCLUSIONS/INTERPRETATION

The patients with type 2 diabetes had no evidence of impaired reflex or autonomic control of heart period variability at a time when there was central sympathetic activation to the periphery. Furthermore, being overweight itself was not associated with sympathetic activation.

Insulin resistant state in type 2 diabetes is related to advanced autonomic neuropathy

To elucidate the relationships between obesity, glycemic control, dyslipidemia, hypertension, microvascular complications, and insulin resistance assessed using an euglycemic hyperinsulinemic clamp technique, we studied 54 hospitalized type 2 diabetic subjects (DM) and 10 age- and sex-matched normotensive, nonobese control subjects (C). Glucose infusion rate (GIR) derived from the clamp study was used as an index of insulin resistance. Body mass index (BMI), the prevalence of hypertension, HbA1c and serum nonesterified fatty acids (NEFA) were significantly higher, and serum high-density-lipoprotein (HDL)-cholesterol was significantly lower in DM than in C (p < 0.05 or less). The median GIR level was significantly lower inDM than in C (p = 0.038). The difference in GIR between the two groups wasstill statistically significant even after adjustment for BMI, mean BP, HbA1c, NEFA, and HDL-cholesterol. However, after simultaneous adjustment for these factors, there was no difference in GIR between the two groups. Body mass index, mean BP, HbA1c, and NEFA showed negative correlations, and serum HDL-cholesterol showed a positive correlation with GIR, but neither age nor duration of diabetes correlated with GIR. When GIR values in DM were divided according to the degree of neuropathy, retinopathy, and nephropathy, and compared to those in C, GIR levels tended to be decreased with increasing severity of each microvascular complication, but there was no difference in median GIR levels among the diabetic subgroups. Relationships between the GIR levels and confounding factors such as age, sex, BMI, mean BP, HbA1c, serum NEFA, and serum HDL-cholesterol, were examined simultaneously with a multiple regression analysis. This analysis revealed that HbA1c and serum NEFA may affect the GIR level. Furthermore, together with these two factors, the relationships between the GIR levels and the severity of each microvascular complication were explored with the same analysis. This model clearly demonstrated that both the decreased CVR-R and pronounced orthostatic fall in systolic BP were independent factors for the decreased GIR. These findings suggest that marked autonomic dysfunction, rather than other confounding factors, is related to increased insulin resistance in DM.

Relationship between autonomic cardiac activity, beta-cell function, anthropometrics and metabolic indices in type II diabetics

OBJECTIVE

Recent studies have demonstrated that C-peptide exerts beneficial effects on the diabetic state, including improvements in kidney and nerve function. Thus, we investigated the effect of residual pancreatic C-peptide secretion on the cardiac autonomic nervous system in well- and poorly controlled type II diabetic patients.

DESIGN

Randomised cross-sectional study.

PATIENTS

Forty type II diabetic patients free from diabetic neuropathy, with similar anthropometric parameters, volunteered for our study.

MEASUREMENTS

Insulin action, residual pancreatic C-peptide secretion and the cardiac autonomic nervous system were investigated by euglycaemic hyperinsulinaemic clamp, glucagon bolus test and heart rate variability, respectively. M-values were used as an index of insulin sensitivity. High frequency (HF) and low frequency (LF) oscillations in heart rate were analysed.

RESULTS

The patients were categorized into those with good (HbA1c < or = 7.0) and poor (HbA1c > or = 8.0) metabolic control. The patients with good metabolic control had fasting plasma glucose and C-peptide levels, plasma area under the curve (auc) insulin and C-peptide levels, M-values, LF values and LF/HF ratio significantly lower than patients with poor metabolic control. In contrast, RR interval, total power and HF values had an opposite trend. Basal plasma C-peptide correlated with LF/HF in patients with good (r = -0.42; P < 0.05) and poor metabolic control (r = -0.45; P < 0.05). An even stronger correlation between auc C-peptide and LF/HF in patients with good (r = -0.53, P < 0.002) and poor metabolic control (r = -0.49; P < 0.03), as well as in the whole group (r = -0.83; P < 0.001) was found. By multiple regression analyses performed in all patients, LF/HF were independently associated with auc C-peptide (t = -8.618; P < 0.001) but not basal C-peptide levels (t = -0.137; P < 0.88).

CONCLUSION

Our study demonstrated that preserved C-peptide secretion is associated with a well balanced cardiac autonomic activity in type II diabetic patients.

Soluble leptin receptor and insulin resistance as determinant of sleep apnea

OBJECTIVE

To investigate the possible associations between sleep apnea syndrome, hyperinsulinemia/insulin resistance and hyperleptinemia in subjects with different degrees of body mass index.

DESIGN

To test for the presence or absence of sleep apnea syndrome in association with hyperinsulinemia/insulin resistance and hyperleptinemia.

SUBJECTS

Twenty subjects with different body mass index (mean BMI 30.9+/-4.2).

MEASUREMENTS

Insulin action and plasma soluble leptin receptor were measured by euglycemic hyperinsulinemic glucose clamp and by ELISA method, respectively. Occurrence of sleep apnea syndrome was assessed by clinical and nocturnal monitoring using a validated sleep apnea recorder.

RESULTS

The apnea/hypopnea index (AHI) was positively correlated with plasma soluble leptin receptor (0.76; P<0.001) and negatively with the degree of insulin-mediated glucose uptake (r=-0.73; P<0.001). In a multivariate analysis AHI was associated with plasma soluble leptin receptor and insulin mediated glucose uptake independently of age, gender, BMI, plasma leptin levels and PaCO(2).

CONCLUSION

Sleep apnea syndrome is associated with plasma soluble leptin receptor and insulin resistance independently of BMI.

Chronic administration of pharmacologic doses of vitamin E improves the cardiac autonomic nervous system in patients with type 2 diabetes

BACKGROUND

Type 2 diabetes is associated with elevated oxidative stress and declines in antioxidant defense. The disease is also characterized by an imbalance in the ratio of cardiac sympathetic to parasympathetic tone. Antioxidants, vitamin E in particular, may have beneficial effects on the cardiac autonomic nervous system through a decline in oxidative stress.

OBJECTIVE

We investigated the possible effects of vitamin E on the cardiac autonomic nervous system, as assessed by analysis of heart rate variability, in patients with type 2 diabetes and cardiac autonomic neuropathy.

DESIGN

In a double-blind randomized controlled trial, 50 patients with type 2 diabetes were assigned to treatment with vitamin E (600 mg/d) or placebo for 4 mo.

RESULTS

The anthropometric characteristics of the patients remained unchanged throughout the study. Chronic vitamin E administration was associated with decreases in concentrations of glycated hemoglobin (P < 0.05), plasma insulin (P < 0.05), norepinephrine (P < 0.03), and epinephrine (P < 0.02); a lower homeostasis model assessment index (P < 0.05); and improved indexes of oxidative stress. Furthermore, vitamin E administration was associated with increases in the R-R interval (P < 0.05), total power (P < 0.05), and the high-frequency component of heart rate variability (HF; P < 0.05) and decreases in the low-frequency component (LF; P < 0.05) and the ratio of LF to HF (P < 0.05). Finally, change in the plasma vitamin E concentration was correlated with change in the LF-HF ratio (r = -0.43, P < 0.04) independently of changes in the homeostasis model assessment index and plasma catecholamines concentrations.

CONCLUSIONS

Chronic vitamin E administration improves the ratio of cardiac sympathetic to parasympathetic tone in patients with type 2 diabetes. Such an effect might be mediated by a decline in oxidative stress.

Insulin sensitivity regulates autonomic control of heart rate variation independent of body weight in normal subjects

It is unclear whether insulin sensitivity independent of body weight regulates control of heart rate variation (HRV) by the autonomic nervous system. Insulin action on whole-body glucose uptake (M-value) and heart rate variability were measured in 21 normal men. The subjects were divided into 2 groups [normally insulin sensitive (IS, 8.0 +/- 0.4 mg/kg.min) and less insulin sensitive (IR, 5.1 +/- 0.3 mg/kg.min)] based on their median M-value (6.2 mg/kg x min). Spectral power analysis of heart rate variability was performed in the basal state and every 30 min during the insulin infusion. The IS and IR groups were comparable, with respect to age (27 +/- 2 vs. 26 +/- 2 yr), body mass index (22 +/- 1 vs. 23 +/- 1 kg/m(2)), body fat (13 +/- 1 vs. 13 +/- 1%), systolic (121 +/- 16 vs. 117 +/- 14 mm Hg) and diastolic (74 +/- 11 vs. 73 +/- 11 mm Hg) blood pressures, and fasting plasma glucose (5.4 +/- 0.1 vs. 5.5 +/- 0.1 mmol/L) concentrations. Fasting plasma insulin was significantly higher in the IR (30 +/- 4 pmol/L) than in the IS (17 +/- 3 pmol/L, P < 0.05) group. In the IS group, insulin significantly increased the normalized low-frequency (LFn) component, a measure of predominantly sympathetic nervous system activity, from 36 +/- 5 to 48 +/- 4 normalized units (nu; 0 vs. 30-120 min, P < 0.001); whereas the normalized high-frequency (HFn) component, a measure of vagal control of HRV, decreased from 66 +/- 9 to 48 +/- 5 nu (P < 0.001). No changes were observed in either the normalized LF component [35 +/- 5 vs. 36 +/- 2 nu, not significant (NS)] or the normalized HF component (52 +/- 6 vs. 51 +/- 4 nu, NS) in the IR group. The ratio LF/HF, a measure of sympathovagal balance, increased significantly in the IS group (0.92 +/- 0.04 vs. 1.01 +/- 0.04, P < 0.01) but remained unchanged in the IR group (0.91 +/- 0.04 vs. 0.92 +/- 0.03, NS). Heart rate and systolic and diastolic blood pressures remained unchanged during the insulin infusion in both groups. We conclude that insulin acutely shifts sympathovagal control of HRV toward sympathetic dominance in insulin-sensitive, but not in resistant, subjects. These data suggest that sympathetic overactivity is not a consequence of hyperinsulinemia.