Increase in systolic blood pressure and catecholamine level during hyperinsulinemia in a placebo-controlled euglycemic clamp in healthy subjects

Impact of 3-year changes in fasting insulin and insulin resistance indices on incident hypertension: Tehran lipid and glucose study

Background

To examine the association between changes in fasting insulin, homeostasis model assessment of insulin resistance (HOMA-IR), and insulin-glucose ratio (IGR) levels, over approximately 3 years with incident hypertension.

Methods

A total of 2814 Iranian participants (1123 men) without hypertension and known diabetes at baseline and the first examination were followed for a median of 6.32 years. The associations between quartiles of changes in fasting insulin and IR indices with incident hypertension were assessed using multivariate Cox proportional hazard regression analyses with first quartile as reference. The models were adjusted for baseline values of insulin or each IR index, and age, sex, smoking, physical activity, educational levels, marital status, history of cardiovascular diseases, baseline levels of systolic and diastolic blood pressures, estimated glomerular filtration rate, triglycerides, total cholesterol, high-density lipoprotein cholesterol, fasting plasma glucose (only for insulin change) and both body mass index (BMI) per se, and its change. Akaike's information criteria (AIC) was applied as indicator for goodness of fit of each predictive model. The discrimination ability of models was calculated using the Harrell's C statistic.

Results

During the study, 594 incident cases of hypertension (253 men) were identified. The 4th quartile of changes in insulin, HOMA-IR, and IGR showed hazard ratios (95% confidence interval) of 1.31 (1.01-1.69), 1.18 (0.92-1.52), and 1.53 (1.18-1.98) for hypertension, respectively, in fully-adjusted models. Changes in fasting insulin levels and IR indices showed significant increasing trends for incident hypertension, moving from 1st to 4th quartiles (all P-values < 0.05). Focusing on model fitness, no superiority was found between changes in fasting insulin, HOMA-IR, and IGR to predict incident hypertension. The discriminatory powers of changes in fasting insulin and IR indices as assessed by C index were similar (i.e. about 80%).

Conclusion

Changes in fasting insulin and IR indices were significantly associated with developing hypertension among normotensive population even after considering BMI changes.

Prehypertension in dyslipidemic individuals; relationship to metabolic parameters and intima-media thickness

INTRODUCTION

Like hypertension, prehypertension is associated with cardiovascular disease.

AIMS

The aim of this study was to evaluate: a) the prevalence of prehypertension/hypertension in individuals with various dyslipidemic phenotypes; b) the relation between blood pressure (BP) and other risk factors for atherosclerosis; c) atherogenic potential of prehypertension by the assessment of intima-media thickness of the arteria carotis communis (IMT).

METHODS

667 clinically asymptomatic subjects were divided into four dyslipidemic phenotypes (DLP) according to apolipoprotein B (apoB) and triglycerides (TG): DLP1 (n=198, normo-apoB/normo-TG), DLP2 (n=179, normo-apoB/hyper-TG), DLP3 (n=87, hyper-apoB/normo-TG), DLP4 (n=203, hyper-apoB/hyper-TG). DLP1 served as a control group.

RESULTS

There was significantly higher prevalence of prehypertension and hypertension in subjects with dyslipidemia (DLP2 43.0%, 41.3%; DLP3 42.5%, 29.9%; DLP4 42.4%, 47.8%) than in normolipidemic individuals (DLP1 32.8%, 20.2%). Systolic and diastolic blood pressure (SBP + DBP) correlated with age, total cholesterol, TG, non-HDL-cholesterol, body mass index and waist circumference; SBP additionally with C-peptide, fasting glycemia; DBP additionally with apoB, homeostasis model assessment (HOMA) and plasminogen activator inhibitor-1. The IMT of hypertensive and of prehypertensive subjects was higher than that of subjects with normal BP in all DLPs.

CONCLUSIONS

The prevalence of prehypertension was higher in all dyslipidemic patients. The common prevalence of prehypertension/hypertension was highest in the hypertriglyceridemic subjects. Prehypertensive and hypertensive patients had higher IMT than normotensive individuals in all DLPs.

Prevalence of and Factors Associated with Hypertension in Young and Old Women with Systemic Lupus Erythematosus

Objective.

Hypertension (HT) is more prevalent in patients with systemic lupus erythematosus (SLE) than among the general population and it has been associated with atherosclerotic cardiovascular diseases in these patients. We examined the proportion of HT and factors associated with it in young and old women with SLE.

Methods.

Participants (112 women with SLE and 223 healthy age-matched women) were categorized as young (age ≤ 40 years) or old (age > 40 years). We compared cardiovascular and specific SLE-related variables and inflammatory markers in hypertensive and normotensive women with SLE for each age range. We also assessed the factors independently associated with HT in the entire cohort and in each age range by means of a multivariate regression analysis.

Results.

The prevalence of HT was higher in women with SLE than in controls (56% vs 29%; p < 0.001), and was proportionally higher in younger women with SLE (40% vs 11%; p < 0.001) than in older women with SLE (74% vs 47%; p = 0.001). After adjustment for potential confounders, HT was associated with renal involvement and higher nonobesity-related insulin levels in younger women with SLE. In older patients, HT was associated with age, renal involvement, and obesity. Finally, in the entire cohort, HT was associated with age, insulin, renal involvement, and the Systemic Lupus Erythematosus Disease Activity Index score.

Conclusion.

An association between HT and insulin has been identified in women with SLE, particularly younger ones. Factors associated with HT in women with SLE differed depending on their age. HT was more prevalent in women with SLE than in control subjects, being proportionally higher in young women with SLE.

Insulin resistance and risk of incident hypertension among men

J Clin Hypertens (Greenwich). 2009;11:483-490. (c) 2009 Wiley Periodicals, Inc.The independent association between insulin resistance and the development of hypertension remains in doubt because insulin resistance correlates with other metabolic factors also proposed to be associated with hypertension. The authors examined the association between the insulin sensitivity index and incident hypertension in a prospective nested case-control study among 1453 men (mean age, 61 years) who participated in the Health Professionals' Follow-up Study. The authors computed the insulin sensitivity index for each man in the study based on fasting insulin and triglyceride levels. Logistic regression was performed conditioned on age and adjusted for standard hypertension risk factors as well as renal function, cholesterol, and uric acid. The insulin sensitivity index was 6% lower in the cases compared with the controls (P<.001). The multivariable odds ratio for hypertension comparing the lowest with highest quartile of insulin sensitivity index was 1.09 (0.71-1.65) among the entire sample. However, the association between the insulin sensitivity index and incident hypertension differed significantly by age (P interaction <.001). Among men younger than 60 years, the multivariable odds ratio for the lowest compared with highest quartile was 1.93 (1.01-3.71) but was 0.67 (0.37-1.24) among older men. Insulin resistance is independently associated with incident hypertension among younger men.

Blood viscosity: Effects of mental stress and relations to autonomic nervous system function and insulin sensitivity

We studied effects of mental stress on whole-blood viscosity (WBV) and blood pressure (BP), and relations between WBV and autonomic nervous system activity and insulin sensitivity. We measured WBV (rotational rheometer), plasma noradrenaline (NA), finger BP, heart rate variability (HRV) and baroreflex sensitivity (BRS; transfer technique) during hyperinsulinaemic glucose clamp and mental arithmetic stress test (MST) in 20 men with high ( > or =140/90 mmHg) and 21 men with normal (< or =115/75 mmHg) screening BP, and 10 women regardless of screening BP (all normotensive). WBV and NA increased during the MST, while HRV and BRS decreased. During the MST, WBV (all shear rates) and the response ((delta)WBV) (low shear) were higher in men with high compared to normal screening BP (p<0.05). In men, WBV correlated positively with NA and negatively with HRV, BRS and insulin sensitivity. The diastolic BP response ((delta)DBP) was independently explained by high-shear (delta)WBV (p<0.05) and (delta)NA (p<0.0001), and (delta)WBV independently by (delta)DBP (p<0.05). WBV is related to increased sympathetic activity, impaired vagal cardiac control and low insulin sensitivity in young adults. The haemorheological effect of mental stress is increased in young men with high screening BP and may be mediated by the acute increase in BP.

Uric acid and insulin sensitivity and risk of incident hypertension

BACKGROUND

Uric acid, insulin sensitivity, and endothelial dysfunction may be important in the development of hypertension. Corresponding circulating biomarkers are associated with risk of hypertension, but because these factors may be interrelated, whether they independently affect risk is unknown.

METHODS

In 1496 women aged 32 to 52 years without hypertension at baseline, we prospectively analyzed the associations between fasting plasma levels of uric acid, insulin, triglycerides, the insulin sensitivity index, and 2 biomarkers associated with endothelial dysfunction (homocysteine and soluble intercellular adhesion molecule-1) and the odds of incident hypertension. Odds ratios were adjusted for standard risk factors and then for all biomarkers plus estimated glomerular filtration rate and total cholesterol level. Population-attributable risk was estimated for biomarkers significantly associated with hypertension.

RESULTS

All the biomarkers were associated with incident hypertension after adjustment for standard hypertension risk factors. However, after simultaneously controlling for all the biomarkers, estimated glomerular filtration rate, and total cholesterol level, only uric acid and insulin levels were independently associated with incident hypertension. Comparing the highest and lowest quartiles of uric acid levels, the odds ratio was 1.89 (95% confidence interval, 1.26-2.82). A similar comparison yielded an odds ratio of 2.03 (95% confidence interval, 1.35-3.05) for insulin levels. Using an estimated basal incidence rate of 14.6 per 1000 annually, 30.8% of all hypertension occurring in young women annually is associated with uric acid levels of 3.4 mg/dL or greater (to convert to micromoles per liter, multiply by 59.485). For insulin levels of 2.9 microIU/mL or greater (to convert to picomoles per liter, multiply by 6.945), this proportion is 24.2%.

CONCLUSIONS

Differences in uric acid and insulin levels robustly and substantially affect the risk of hypertension in young women. Measuring these biomarkers in clinical practice may identify higher-risk individuals.

Immediate but not long-term intranasal administration of insulin raises blood pressure in human beings

Intranasal administration of insulin has been shown to influence neuroendocrine functions via an effect on central nervous mechanisms. Because insulin, in particular when infused into cerebral arteries, induces blood pressure (BP) elevation by an unknown mechanism, we investigated whether insulin exerts similar effects on BP after intranasal administration. To evaluate the immediate effects of insulin on BP, 20 IU of human insulin was intranasally administered every 10 minutes over a 2-hour period. Blood pressure, heart rate, and muscular sympathetic nervous activity (MSNA) were continuously monitored. For evaluating the effects of subchronic administration of insulin, changes during and after 8 weeks of treatment with 160 IU insulin/d on BP were monitored. Compared with placebo, the immediate nasal administration of insulin raised diastolic BP (12.21% +/- 5.10%; P < .05), mean arterial BP (10.81% +/- 4.32%; P < .04), and systolic BP (9.53% +/- 4.66%; P < .08), whereas MSNA and heart rate were unaffected. In contrast, prolonged intranasal insulin administration did not affect BP (P > .62 for all comparisons). The immediate increase in BP in the face of an unsuppressed MSNA after insulin suggests that intranasal insulin transiently changes the baroreflex set point. Thus, data suggest that intranasal insulin administration affects BP regulatory centers in the brain. However, the effect is not observed with prolonged administration of the hormone, suggesting the emergence of counterregulatory processes.

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.