Hypertension, Insulin Resistance, and Aldosterone: Sex-Specific Relationships

Additive interactions between obesity and insulin resistance on hypertension in a Chinese rural population

BACKGROUND

Adiposity and insulin resistance (IR) are closely associated with hypertension; however, the role of interactions between obesity phenotypes and IR in hypertension is unclear. This study aimed to evaluate the interactions of body mass index (BMI), waist circumference (WC), and body fat percentage (BF%) with IR on hypertension risk.

METHODS

We analyzed data from 4888 participants (mean age 57 years, 41.2% men) in the China Northwest Natural Population Cohort, Ningxia Project. BMI, WC, and BF% were determined using bioelectrical impedance analysis devices. IR was estimated using a homeostasis model assessment index (HOMA-IR). Multivariable-adjusted logistic regression was used to evaluate the association between HOMA-IR and hypertension risk. We calculated the relative excess risk and attributable proportion with their 95% confidence intervals (CIs) to assess whether adiposity phenotypes modified the effect of HOMA-IR on hypertension risk.

RESULTS

The crude prevalence of hypertension was 52.2%. The multivariable-adjusted odds ratio of HOMA-IR was 1.80 (95% CI: 1.23-2.65) for the risk of hypertension in the highest versus the lowest quartiles, but this association became marginal in models further adjusting for BMI, WC, and BF% (P for trend = 0.056). Relative excess risk and attributable proportion for interaction between high HOMA-IR and high BF% were 0.32 (0.04-0.59) and 0.33 (0.06-0.60), respectively. Additionally, high truncal and leg BF% and high HOMA-IR accounted for the hypertension risk in women, but not in men. We did not observe any significant interactions between BMI or WC and HOMA-IR on hypertension.

CONCLUSION

BF% modified the association between IR and increased risk of hypertension in women with high truncal and leg BF%, but not in men.

Comparison between distinct insulin resistance indices in measuring the development of hypertension: The China Health and Nutrition Survey

Aim

Our aim was to identify the relationship between several surrogate insulin resistance (IR) indices based on lipid products and the development of hypertension.

Materials and methods

A total of 3,281 participants aged ≥ 18 years enrolled in the China Health and Nutrition Survey from 2009 to 2015 and who were followed up for 6 years were included in the final analysis. Logistic regression was used to analyze the association between different IR indices and incident hypertension.

Results

There were 882 (28.9%) hypertensive participants in 2015. With regard to the homeostasis model assessment of insulin resistance (HOMA-IR) based on insulin level, subjects in the highest quartile of HOMA-IR values were more likely to develop hypertension [RR = 1.58 (1.26–1.98), P < 0.001] after being adjusted by sex and age, smoke habits, alcohol consumption, community type, married status, and education years in 2009. Subjects in the highest quartile of the triglyceride-glucose index (TyG) combined with body mass index (BMI) and waist circumference (WC) had more than two times the risk of hypertension after full adjustment compared with individuals in the lowest quartile (both P < 0.001), and the trend continued when adjusted for the HOMA-IR. Compared with those in the lowest quartile of TyG-BMI values, females in the highest quartile had a higher risk of developing hypertension than males [2.82 (2.01–3.97) vs. 2.56 (1.80–3.64)] after the full adjustment, and the trend existed independent of IR. Young participants in the highest quartile of the HOMA-IR had significantly higher risks of hypertension compared with subjects in the lowest quartile [1.67 (1.31–2.14), P < 0.005], and this trend was not significant in the elderly participants.

Conclusion

The results from our large-scale study elucidate the superiority of the TyG-BMI and TyG-WC compared with the HOMA-IR in the prediction of hypertension, which may be related to lipid deposition. The sex-specific predictive value is distinct for different IR indicators.

Unique Associations of DNA Methylation Regions With 24-Hour Blood Pressure Phenotypes in Blacks

BACKGROUND

Epigenetic marks (eg, DNA methylation) may capture the effect of gene-environment interactions. DNA methylation is involved in blood pressure (BP) regulation and hypertension development; however, no studies have evaluated its relationship with 24-hour BP phenotypes (daytime, nighttime, and 24-hour average BPs).

METHODS

We examined the association of whole blood DNA methylation with 24-hour BP phenotypes and clinic BPs in a discovery cohort of 281 Blacks using reduced representation bisulfite sequencing. We developed a deep and region-specific methylation sequencing method, Bisulfite ULtrapLEx Targeted Sequencing and utilized it to validate our findings in a separate validation cohort (n=117).

RESULTS

Analysis of 38 215 DNA methylation regions (MRs), derived from 1 549 368 CpG sites across the genome, identified up to 72 regions that were significantly associated with 24-hour BP phenotypes. No MR was significantly associated with clinic BP. Two to 3 MRs were significantly associated with various 24-hour BP phenotypes after adjustment for age, sex, and body mass index. Together, these MRs explained up to 16.5% of the variance of 24-hour average BP, while age, sex, and BMI explained up to 11.0% of the variance. Analysis of one of the MRs in an independent cohort using Bisulfite ULtrapLEx Targeted Sequencing confirmed its association with 24-hour average BP phenotype.

CONCLUSIONS

We identified several MRs that explain a substantial portion of variances in 24-hour BP phenotypes, which might be excellent markers of cumulative effect of factors influencing 24-hour BP levels. The Bisulfite ULtrapLEx Targeted Sequencing workflow has potential to be suitable for clinical testing and population screenings on a large scale.

Association of renin and aldosterone with glucose metabolism in a Western European population: the KORA F4/FF4 study

INTRODUCTION

Primary aldosteronism is associated with impaired glucose tolerance. Whether plasma aldosterone and/or renin concentrations are associated with type 2 diabetes and continuous measures of glucose metabolism in the general population is still under debate.

RESEARCH DESIGN AND METHODS

The analyses included 2931 participants of the KORA F4 study at baseline and 2010 participants of the KORA FF4 study after a median follow-up of 6.5 years. The associations of active plasma renin and aldosterone concentrations with type 2 diabetes and continuous measures of glucose metabolism were assessed using logistic and linear regression models. Results were adjusted for sex, age, body mass index (BMI), estimated glomerular filtration rate, potassium, use of ACE inhibitors, angiotensin receptor blockers, beta blockers, diuretics and calcium channel blockers.

RESULTS

Cross-sectionally, renin was associated with type 2 diabetes (OR per SD: 1.25, 95% CI 1.10 to 1.43, p<0.001), fasting glucose, 2-hour glucose, insulin, proinsulin, HOMA-B (homeostasis model assessment of beta cell function) and HOMA-IR (homeostasis model assessment of insulin resistance) (all p values <0.001). Aldosterone was not associated with type 2 diabetes (OR: 1.04, 95% CI 0.91 to 1.19; p=0.547) but with insulin, proinsulin and HOMA-IR (all p values <0.001). The aldosterone-renin ratio was inversely associated with type 2 diabetes and several measures of glucose metabolism. Longitudinally, neither renin (OR: 1.12, 95% CI 0.92 to 1.36) nor aldosterone (OR: 0.91, 95% CI 0.74 to 1.11) were associated with incident type 2 diabetes. Renin was inversely associated with changes of insulin concentrations.

CONCLUSIONS

In the KORA F4/FF4 study, renin and aldosterone were not associated with incident type 2 diabetes and largely unrelated to changes of measures of glucose metabolism. Cross-sectionally, aldosterone was associated with surrogate parameters of insulin resistance. However, these associations were not independent of renin.

Associations of Insulin Resistance With Systolic and Diastolic Blood Pressure: A Study From the HCHS/SOL

[Figure: see text].

Gender differences in human adrenal cortex and its disorders

The adrenal cortex plays pivotal roles in the maintenance of blood volume, responsiveness to stress and the development of gender characteristics. Gender differences of human adrenal cortex have been recently reported and attracted increasing interests. Gender differences occur from the developing stage of the adrenal, in which female subjects had more activated stem cells with higher renewal capacity resulting in gender-associated divergent structures and functions of cortical zonations of human adrenal. Female subjects generally have the lower blood pressure with the lower renin levels and ACE activities than male subjects. In addition, HPA axis was more activated in female than male, which could possibly contribute to gender differences in coping with various stressful events in our life. Of particular interest, estrogens were reported to suppress RAAS but activate HPA axis, whereas androgens had opposite effects. In addition, adrenocortical disorders in general occur more frequently in female with more pronounced adrenocortical hormonal abnormalities possibly due to their more activated WNT and PRK signaling pathways with more abundant activated adrenocortical stem cells present in female adrenal glands. Therefore, it has become pivotal to clarify the gender influence on both clinical and biological features of adrenocortical disorders. We herein reviewed recent advances in these fields.

Aldosterone-to-renin ratio is related to arterial stiffness when the screening criteria of primary aldosteronism are not met

Aldosterone-to-renin ratio (ARR) is a screening tool for primary aldosteronism (PA), but the significance of ARR when the PA criteria are not met remains largely unknown. In this cross-sectional study we investigated the association of ARR with haemodynamic variables in 545 normotensive and never-medicated hypertensive subjects (267 men, 278 women, age range 19-72 years) without suspicion of PA. Supine haemodynamic data was recorded using whole-body impedance cardiography and radial tonometric pulse wave analysis. In sex-adjusted quartiles of ARR, determined as serum aldosterone to plasma renin activity ratio, the mean values were 282, 504, 744 and 1467 pmol/µg of angiotensin I/h, respectively. The only difference in haemodynamic variables between the ARR quartiles was higher pulse wave velocity (PWV) in the highest quartile versus other quartiles (p = 0.004), while no differences in blood pressure (BP), heart rate, wave reflections, cardiac output or systemic vascular resistance were observed between the quartiles. In linear regression analysis with stepwise elimination, ARR was an independent explanatory factor for PWV (β = 0.146, p < 0.001, R2 of the model 0.634). In conclusion, ARR was directly and independently associated with large arterial stiffness in individuals without clinical suspicion of PA. Therefore, ARR could serve as a clinical marker of cardiovascular risk.Trial registration: ClinicalTrails.gov: NCT01742702.

Age- and sex-specific reference ranges are needed for the aldosterone/renin ratio

OBJECTIVE

Current Endocrine Society Clinical Practice Guidelines use a specific aldosterone/renin ratio (ARR) threshold to screen for primary aldosteronism (a treatable disease causing up to 15% of hypertension in primary care) in all patients. We sought to characterize demographic variations in the ARR, hypothesizing a need for age- and sex-specific reference ranges to improve the accuracy of the test.

DESIGN

Retrospective cross-sectional analysis of ARR measurements at a single tertiary hospital from December 2016 to June 2018.

PATIENTS

A total of 442 patients with clinically indicated ARR were included, after excluding those who were on spironolactone or the oral contraceptive pill, were pregnant or had an existing adrenal condition.

MEASUREMENTS

Aldosterone, renin and the ARR.

RESULTS

Among those aged 20-39 years (n = 74), females had significantly higher median aldosterone (369 vs 244 pmol/L, P = .028), lower median renin (17.0 vs 27.6 mIU/L, P = .034) and higher median ARR (20.7 vs 10.3 (pmol/L)/(mIU/L), P = .001) than males, despite having lower systolic (135 vs 145 mmHg, P = .021) and diastolic (89 vs 96.5 mmHg, P = .007) blood pressure. The ≥ 60-year age group (n = 157) also had significant sex differences in the ARR. With increasing age (20-39 vs ≥ 60 years), there was a significant fall in plasma aldosterone in females (369 pmol/L vs 264 pmol/L, P = .005), with no change observed in males.

CONCLUSIONS

For those 20-39 years old, aldosterone and the ARR are significantly higher in females despite a lower systolic and diastolic BP, highlighting the potential for false-positive results. Our findings indicate the need for prospective studies with a control population to define age- and sex-specific ARR reference ranges.

Twenty-four-hour versus clinic blood pressure levels as predictors of long-term cardiovascular and renal disease outcomes among African Americans

In Caucasian and Asian populations, evidence suggests that 24-h blood pressures (BP) are more predictive of long-term cardiovascular events than clinic BP. However, few long-term studies have evaluated the predictive value of 24-h BP phenotypes (24-h, daytime, nighttime) among African Americans (AA). The purpose of this study is to evaluate the added value of 24-h BP phenotypes compared to clinic BP in predicting the subsequent fatal and non-fatal cardiovascular/renal disease events in AA subjects. AA subjects (n = 270) were initially studied between 1994 and 2006 and standardized clinic BP measurements were obtained during screening procedures for a 3-day inpatient clinical study during which 24-h BP measurements were obtained. To assess the subsequent incidence of cardiovascular and renal disease events, follow-up information was obtained and confirmed by review of paper and electronic medical records between 2015 and 2017. During a mean follow-up of 14 ± 4 years, 50 subjects had one or more fatal or non-fatal cardiovascular/renal disease events. After adjustment for covariates, clinic systolic and diastolic BP were strongly associated with cardiovascular/renal disease events and all-cause mortality (p < 0.0001). Twenty-four-hour BP phenotypes conferred a small incremental advantage over clinic BP in predicting cardiovascular/renal events, which was limited to making a difference of one predicted event in 250-1,000 predictions depending on the 24-h BP phenotype. Nocturnal BP was no more predictive than the other 24-h BP phenotypes. In AA, 24-h BP monitoring provides limited added value as a predictor of cardiovascular/renal disease events. Larger studies are needed in AA to confirm these findings.

Sex specific impact of different obesity phenotypes on the risk of incident hypertension: Tehran lipid and glucose study

Background

To investigate the association between different obesity phenotypes and the risk of incident hypertension among both genders.

Methods

The study population included 3659 Iranians (men = 1540), aged ≥20 years free of hypertension at baseline. Participants were classified into six categories of body mass index (BMI)-metabolic health status, in which unhealthy metabolic status was defined based on the presence of > 1 component of metabolic syndrome (MetS) using the joint interim statement (JIS) criteria or the presence of insulin resistance (IR). The association between different obesity phenotypes and incident hypertension was assessed using multivariate Cox's proportional hazard models adjusted for age, current smoking, low physical activity, diabetes mellitus, family history of premature cardiovascular disease, estimated glomerular filtration rate, phase of recruitment, BMI and systolic blood pressure, considering metabolically healthy normal weight group as the reference.

Results

After a median follow-up of 11.6 years 1122 participants (men = 493) experienced hypertension. Using JIS criteria, a significant higher risk of hypertension was observed among metabolically healthy obese and well as metabolically unhealthy groups among men in the age adjusted model; however, a significant higher risk in the fully adjusted model was seen among women in the metabolically healthy obese [hazard ratio (HR) 95% confidence interval (CI) 1.96(1.16-3.32)] as well as metabolically unhealthy normal weight [1.98(1.37-2.86)], overweight [2.08(1.49-2.90)] and obese [2.06(1.27-3.30)] groups. Using insulin sensitive normal weight group as the reference, among men, being overweight or obese with and without IR was significant predictors of incident hypertension in the age adjusted model; however, among women, insulin resistant overweight [1.46(1.06-2.02)] and obese groups, [1.63(1.01-2.62)] showed significant risk in the fully adjusted model.

Conclusion

We concluded that first, there was significant difference between genders in the associations between obesity phenotypes and incident hypertension. Second, in general, metabolic status defined by MetS components as compared to IR could do better in identifying high risk women for hypertension. Third, women populations who are metabolically healthy obese using MetS definition or those with either > 1 component of metabolic syndrome or overweight/obese ones with IR should be prioritized for implementing urgent preventive strategies against hypertension focusing on lifestyle changes.

Links between aldosterone excess and metabolic complications: A comprehensive review

Shortly after the first description of primary aldosteronism (PA) appeared in the 1950s by Jerome Conn, an association of the condition with diabetes mellitus was documented. However, a clear pathophysiological interrelationship linking the two entities has yet to be established. Nevertheless, so far, many mechanisms contributing to insulin resistance and dysregulation of glucose uptake have been described. At the same time, many observational studies have reported an increased prevalence of the metabolic syndrome (MetS) among patients with PA. Regarding the relationship between aldosterone levels and obesity, a vicious cycle of adipokine-induced aldosterone production and aldosterone adipogenic action may be further contributing to MetS manifestations in PA patients. However, whether aldosterone excess affects lipid metabolism is still under investigation. Also, recent findings of the coexistence of glucocorticoid excess in many cases of PA highlight the need for further studies to examine the presumed link between high aldosterone levels and various metabolic parameters. In the present review, our focus is to comprehensively present the spectrum of available research findings concerning the possible associations between aldosterone excess and metabolic alterations, including impaired glucose metabolism, insulin resistance and, consequently, diabetes, altered lipid metabolism and the development of fatty liver. In addition, the complex relationship between obesity and aldosterone is discussed in detail.

Effect of gender and adiposity on in vivo vascular function in young African Americans

The relationship between obesity and high blood pressure is not as strong among African Americans (AA) as compared to Caucasians. We designed the current study to determine the effect of adiposity on vascular endothelial function (a harbinger of hypertension) among young healthy AA without additional cardiovascular disease risk factors. A total of 108 AA subjects (46 women) between the ages of 18 and 45 years were recruited. All the subjects were normotensive, nonsmokers, and normoglycemic. Anthropometric and cardiovascular disease risk factor measurements (lipid, insulin resistance, and inflammatory markers) were obtained. Vascular endothelial function was measured by brachial artery flow-mediated dilation (FMD). Adiposity distribution was measured by using magnetic resonance imaging scan. There were no gender differences in age and levels of blood pressure, lipids, insulin resistance, and inflammatory markers. Women had higher total body fat percentage and higher peripheral adiposity compared to men. We observed that total and central adiposity did not correlate significantly with brachial artery FMD in women (r = -0.12 and r = 0.23, respectively; P = NS). However, in men, waist circumference was positively associated with FMD (r = 0.3, P ≤ .05). Hyperemic flow was negatively correlated significantly with total and central adiposity in men (r = -0.34 and r = -0.48, respectively; P < .05), but not in women (r = -0.26 and r = 0.03, respectively; P = NS). Our study suggests that increased adiposity may pose greater risk to AA men compared to AA women by adversely affecting resistance vessel function (as measured by hyperemic flow). Larger studies are necessary to validate these findings.

Fasting insulin, insulin resistance and risk of hypertension in the general population: A meta-analysis

BACKGROUND

Studies on the association of fasting insulin concentrations or insulin resistance with subsequent risk of hypertension have yielded conflicting results.

OBJECTIVE

To quantitatively assess the association of fasting insulin concentrations or homeostasis model assessment insulin resistance (HOMA-IR) with incident hypertension in a general population by performing a meta-analysis.

METHODS

We searched the PubMed and Embase databases until August 31, 2016 for prospective observational studies investigating the elevated fasting insulin concentrations or HOMA-IR with subsequent risk of hypertension in the general population. Pooled risk ratio (RR) and 95% confidence interval (CI) of hypertension was calculated for the highest versus the lowest category of fasting insulin or HOMA-IR.

RESULTS

Eleven studies involving 10,230 hypertension cases were identified from 55,059 participants. Meta-analysis showed that the pooled adjusted RR of hypertension was 1.54 (95% CI 1.34-1.76) for fasting insulin concentrations and 1.43 (95% CI 1.27-1.62) for HOMA-IR comparing the highest to the lowest category. Subgroup analysis results showed that the association of fasting insulin concentrations with subsequent risk of hypertension seemed more pronounced in women (RR 2.07; 95% CI 1.19-3.60) than in men (RR 1.48; 95% CI 1.17-1.88).

CONCLUSIONS

This meta-analysis suggests that elevated fasting insulin concentrations or insulin resistance as estimated by homeostasis model assessment is independently associated with an exacerbated risk of hypertension in the general population. Early intervention of hyperinsulinemia or insulin resistance may help clinicians to identify the high risk of hypertensive population.

Plasma Renin Activity and Resting Heart Rate in a Population of Community-Dwelling Japanese: The Tanushimaru Study

BACKGROUND

Heart rate is a strong predictor of mortality and development of obesity and diabetes. The renin-angiotensin-aldosterone system plays an important role in blood pressure control and volume homeostasis. Although many studies have indicated the association between aldosterone and hypertension or insulin resistance, epidemiological evidence of the association of heart rate with plasma renin activity (PRA) remains scant. Therefore, we investigated whether heart rate is associated with PRA.

METHODS

A total of 1,943 subjects were enrolled, who underwent a health examination in Tanushimaru in 2009. Plasma renin and aldosterone concentrations were measured by radioimmunoassay. PRA and the homeostasis model assessment (HOMA) were used by natural-log transformed. Resting heart rate was measured using electrocardiography.

RESULTS

We divided the subjects into four groups by heart rate (<60/min, 60-69/min, 70-79/min, ≥80/ min), and analyzed an association between PRA and heart rate by analysis of covariance after adjustments for age and sex. The adjusted mean PRA and HOMA index showed a significant trend (P < 0.01) as higher heart rate, although there was no significant trend between aldosterone and heart rate (P = 0.26). In multiple linear regression analysis adjusted for age, sex, systolic blood pressure, HOMA index, and hypertensive medication, PRA was positively and strongly associated with elevated heart rate (P < 0.01).

CONCLUSIONS

This epidemiological study demonstrated that PRA, but not aldosterone, is significantly and positively associated with higher resting heart rate in a general population.

Effects of aldosterone on insulin sensitivity and secretion

Dr. Conn originally reported an increased risk of diabetes in patients with hyperaldosteronism in the 1950s, although the mechanism remains unclear. Aldosterone-induced hypokalemia was initially described to impair glucose tolerance by impairing insulin secretion. Correction of hypokalemia by potassium supplementation only partially restored insulin secretion and glucose tolerance, however. Aldosterone also impairs glucose-stimulated insulin secretion in isolated pancreatic islets via reactive oxygen species in a mineralocorticoid receptor-independent manner. Aldosterone-induced mineralocorticoid receptor activation also impairs insulin sensitivity in adipocytes and skeletal muscle. Aldosterone may produce insulin resistance secondarily by altering potassium, increasing inflammatory cytokines, and reducing beneficial adipokines such as adiponectin. Renin-angiotensin system antagonists reduce circulating aldosterone concentrations and also the risk of type 2 diabetes in clinical trials. These data suggest that primary and secondary hyperaldosteronism may contribute to worsening glucose tolerance by impairing insulin sensitivity or insulin secretion in humans. Future studies should define the effects of MR antagonists and aldosterone on insulin secretion and sensitivity in humans.

Insulin resistance status and four-year changes in other cardiometabolic risk factors in West-African adults: the Benin study

BACKGROUND

The association of insulin resistance (IR) with other cardiometabolic risk (CMR) factors in sub-Saharan Africans is poorly documented. This study examined the links between IR and the evolution of blood pressure (BP), glycaemia, serum lipids and abdominal obesity in the population of Benin.

DESIGN

Population-based longitudinal study.

METHODS

This study initially included 541 apparently healthy Beninese adults (50% women) aged 25-60 years who were randomly selected in a large city, a small town and a rural area. After a baseline survey, our subjects were followed up after 2 years, and again at 4 years. IR based on homeostasis model assessment (HOMA), blood glucose, BP, waist circumference (WC), triglycerides, total cholesterol and HDL-cholesterol were measured. Complete data at the end of the follow-up periods was available for 416 subjects.

RESULTS

IR was more prevalent in women than in men (33.2% versus 17.8%) and it was generally associated with more adverse values of CMR factors, excepting BP. In controlling for baseline age, sex, WC, diet, lifestyle variables and WC changes; the relative risk (RR) of hyperglycemia over 4 years was as least 3-fold in IR subjects, compared to normal subjects. The RR of abdominal obesity was 5.3 (1.04-26.93) in IR women, compared to non-IR. The association of IR with the evolution of dyslipidemia was inconsistent, but IR tended to exacerbate low HDL-cholesterol.

CONCLUSION

Over 4 years, IR exacerbated hyperglycemia in both men and women, and abdominal obesity in women, but IR did not affect blood pressure. Further research on the link found between IR and dyslipidemia, particularly low HDL-C, is needed in sub-Saharan Africa.

Fasting insulin level is positively associated with incidence of hypertension among American young adults: a 20-year follow-up study

OBJECTIVE

Although hyperinsulinemia, a surrogate of insulin resistance, may play a role in the pathogenesis of hypertension (HTN), the longitudinal association between fasting insulin level and HTN development is still controversial. We examined the relation between fasting insulin and incidence of HTN in a large prospective cohort.

RESEARCH DESIGN AND METHODS

A prospective cohort of 3,413 Americans, aged 18-30 years, without HTN in 1985 (baseline) were enrolled. Six follow-ups were conducted in 1987, 1990, 1992, 1995, 2000, and 2005. Fasting insulin and glucose levels were assessed by a radioimmunoassay and hexokinase method, respectively. Cox proportional hazards models were used to calculate hazard ratios (HRs) and 95% CIs of incident HTN (defined as the initiation of antihypertensive medication, systolic blood pressure ≥140 mmHg, or diastolic blood pressure ≥90 mmHg).

RESULTS

During the 20-year follow-up, 796 incident cases were identified. After adjustment for potential confounders, participants in the highest quartile of insulin levels had a significantly higher incidence of HTN (HR 1.85 [95% CI 1.42-2.40]; P(trend) < 0.001) compared with those in the lowest quartile. The positive association persisted in each sex/ethnicity/weight status subgroup. A similar dose-response relation was observed when insulin-to-glucose ratio or homeostatic model assessment of insulin resistance was used as exposure.

CONCLUSIONS

Fasting serum insulin levels or hyperinsulinemia in young adulthood was positively associated with incidence of HTN later in life for both men and women, African Americans and Caucasians, and those with normal weight and overweight. Our findings suggested that fasting insulin ascertainment may help clinicians identify those at high risk of HTN.

Role of mineralocorticoid receptor in insulin resistance

PURPOSE OF REVIEW

Recent data suggest that mineralocorticoid receptor activation can affect insulin resistance independent of its effects on blood pressure. This review discusses new evidence linking mineralocorticoid receptor to insulin resistance and the underlying mechanisms of these effects.

RECENT FINDINGS

Observational studies have shown mineralocorticoid activity to be associated with insulin resistance irrespective of race, blood pressure or body weight. Increased mineralocorticoid activity may be the common link between obesity, hypertension, dyslipidemia and insulin resistance, features that make up the metabolic syndrome. Treatment of primary aldosteronism is associated with a decrease in insulin resistance and provides one of the most convincing evidences in favor of the contribution of mineralocorticoid receptor to insulin resistance. Dietary salt restriction, which increases aldosterone levels, is also associated with an increase in insulin resistance. Potential mechanisms by which mineralocorticoid receptor may contribute to insulin resistance include a decreased transcription of the insulin receptor gene, increased degradation of insulin receptor substrates, interference with insulin signaling mechanisms, decreased adiponectin production and increased oxidative stress and inflammation. Advantages of mineralocorticoid receptor antagonists on insulin resistance have been demonstrated in animal models.

SUMMARY

There may be a benefit of mineralocorticoid receptor antagonists in human insulin resistance states, but more clinical research is needed to explore these possibilities.

Plasma aldosterone levels and development of insulin resistance: prospective study in a general population

Aldosterone plays a role in hypertension, and hypertension is prevalent in patients with insulin resistance. Cross-sectional studies have reported that plasma aldosterone levels are higher in patients with insulin resistance. However, it is not known whether plasma aldosterone levels predict the development of insulin resistance. Subjects of the present study were 1235 local residents (490 men and 745 women) who participated in health screenings in Japan in 1999. Plasma aldosterone levels were measured by radioimmunoassay. We investigated the cross-sectional relationship between plasma aldosterone levels and insulin resistance (homeostasis model assessment index ≥1.73 according to the diagnostic criteria used in Japan) in 1088 nondiabetic participants. At the 10-year follow-up, 141 subjects had died, and 260 subjects refused re-examination. We performed a prospective analysis of 564 subjects to predict incident insulin resistance. We found a significant (P<0.001) cross-sectional relationship between plasma aldosterone and homeostasis model assessment index at baseline. In the prospective analysis, a significantly higher (P<0.05) relative risk (1.71 [95% CI: 1.03-2.84]) was observed in the highest tertile versus lowest tertile of plasma aldosterone for the development of insulin resistance, after adjustment for confounding factors. This 10-year prospective study demonstrated that plasma aldosterone levels predicted the development of insulin resistance in a general population.

Cardiovascular correlates of insulin resistance in normotensive and hypertensive African Americans

Insulin resistance (IR) is associated with obesity and predisposes to diabetes mellitus (DM) and cardiovascular disease. The purpose of this study is to determine if IR is related to cardiovascular function independent of DM or hypertension among African Americans (AA). Four hundred sixty-two nondiabetic AA (50% hypertensive and 51% women) were studied on an inpatient General Clinical Research Center. Measurements included anthropometrics and 24-hour blood pressure (BP), heart rate (HR), fasting blood glucose, plasma aldosterone, and insulin. Stroke volume (SV) and cardiac output (CO) were measured by impedance plethysmography; peripheral vascular resistance (PVRI) and vascular compliance indices (VCI) were computed. These measurements were also obtained in response to mental (computerized math testing) and pharmacologic (graded norepinephrine infusion) stress. Insulin resistance was calculated using the homeostasis model assessment (HOMA-IR). SV, CO, and VCI decreased with increasing HOMA-IR, whereas HR and PVRI increased. Overall, BP, HR, and PVRI were positively correlated with HOMA-IR (P < .01); and SV index, cardiac index, and VCI were negatively correlated with HOMA-IR (P < .0001). The correlations persisted after adjustment for BP, age, sex, plasma aldosterone, total cholesterol, or low-density lipoprotein and high-density lipoprotein cholesterol. In addition, multiple linear regression analyses showed that HOMA-IR contributes to the maximum variability of all the hemodynamic variables. Blood pressure responses to math stress and norepinephrine infusion did not correlate with HOMA-IR. Unrelated to DM and BP, IR is associated with increased PVRI and decreased CO in AA. These observations suggest that an exclusive focus on effects of IR on DM or BP may ignore independent pathophysiologic contributions of IR to cardiovascular disease.

Stimulus response of blood pressure in black and white young individuals helps explain racial divergence in adult cardiovascular disease: the Bogalusa Heart Study

Blood pressure (BP) is a highly variable physiologic trait with short-term and long-term fluctuations within the same individual at different time points. The burden of BP on the cardiovascular (CV) system has been studied in terms of multiple cross-sectional BP measurements at rest, response of BP to stresses, and long-term longitudinal variability of BP. Observations from childhood are available extending into early middle age in the biracial (black-white) population of Bogalusa, Louisiana. Left ventricular mass index was used to illustrate damaging effects on the CV system by both resting BP levels and fluctuations. Long-term BP variability reflecting intermittent and repeated variability was shown to have a greater effect in blacks. The childhood BP response to several stressors was found to be greater in blacks. These observations suggest that, although at rest a greater vagal effect occurs in blacks, they show a greater response when reacting to a stimulus. This, along with aspects such as carbohydrate-insulin metabolism or other biochemical/physiological differences, may account for the greater acceleration of CV atherosclerosis in blacks. The racial contrasts suggest, in part, that effects of lipoproteins may be greater in whites, whereas the effects of excess BP levels and variability of BP and Na(+)-K(+) intake and diet as well as other environmental effects result in more CV damage in blacks. The strong association of hemodynamic measures with anatomic, metabolic, and environmental factors emphasizes the need to begin prevention of risk factors at an early age. Taken together, understanding racial (black-white) contrasts to stress contribute to both prevention and treatment of hypertension, especially for black males.

Obesity-related hypertension: epidemiology, pathophysiology, and clinical management

The prevalence of obesity, including childhood obesity, is increasing worldwide. Weight gain is associated with increases in arterial pressure, and it has been estimated that 60-70% of hypertension in adults is attributable to adiposity. Centrally located body fat, associated with insulin resistance and dyslipidemia, is a more potent determinant of blood pressure elevation than peripheral body fat. Obesity-related hypertension may be a distinct hypertensive phenotype with distinct genetic determinants. Mechanisms of obesity-related hypertension include insulin resistance, sodium retention, increased sympathetic nervous system activity, activation of renin-angiotensin-aldosterone, and altered vascular function. In overweight individuals, weight loss results in a reduction of blood pressure, however, this effect may be attenuated in the long term. An increasing number of community-based programs (including school programs and worksite programs) are being developed for the prevention and treatment of obesity. Assessment and treatment of the obese hypertensive patient should address overall cardiovascular disease (CVD) risk. There are no compelling clinical trial data to indicate that any one class of antihypertensive agents is superior to others, and in general the principles of pharmacotherapy for obese hypertensive patients are not different from nonobese patients. Future research directions might include: (i) development of effective, culturally sensitive strategies for the prevention and treatment of obesity; (ii) clinical trials to identify the most effective drug therapies for reducing CVD in obese, hypertensive patients; (iii) continued search for the genetic determinants of the obese, hypertensive phenotype.

Hepatic steatosis in overweight/obese females: New screening method for those at risk

AIM: To identify which parameters could help to distinguish the “metabolically benign obesity”, which is not accompanied by insulin resistance (IR) and early atherosclerosis.

METHODS: Eighty two of 124 overweight/obese females formed the study population, which was divided into two groups (52 and 30 subjects, respectively) with and without IR according to a HO meostatic Metabolic Assessment (HOMA) cut-off of 2, and were studied in a cross-sectional manner. The main outcome measures were waist circumference, serum uric acid, high-density lipoprotein-cholesterol and triglycerides, alanine aminotransferase, blood pressure and the two imaging parameters, hepatic steatosis and longitudinal diameter of the spleen, which were measured in relation to the presence/absence of IR.

RESULTS: A variable grade of visceral obesity was observed in all subjects with the exception of three. Obesity of a severe grade was represented more in the group of IR individuals (P = 0.01). Hepatic steatosis, revealed at ultrasound, was more pronounced in IR than in non-IR subjects (P = 0.005). The two groups also demonstrated a clear difference in longitudinal spleen diameter and blood pressure, with raised and significant values in the IR group. Metabolic syndrome was frequent in the IR group, and was not modified when adjusted for menopause (P = 0.001). At linear regression, the β values of waist circumference and body mass index predicting HOMA were 0.295, P = 0.007 and 0.41, P = 0.0001, respectively. Measures of spleen longitudinal diameter were well predicted by body mass index (BMI) values, β = 0.35, P = 0.01, and by HOMA, β = 0.41, P = 0.0001. Blood pressure was predicted by HOMA values, β = 0.39, P = 0.0001). HOMA and hepatic steatosis were highly associated (rho = 0.34, P = 0.002). Interestingly, IR patients were almost twice as likely to have hepatic steatosis as non-IR patients. Among the MS criteria, blood pressure was very accurate in identifying the presence of IR (AUROC for systolic blood pressure 0.66, cut-off 125 mm of Hg, sensibility 64%, specificity 75%; AUROC for diastolic blood pressure 0.70, cut-off 85 mm of Hg, sensibility 54.5%, specificity 75%).

CONCLUSION: As health care costs are skyrocketing, reliable and mainly inexpensive tools are advisable to better define subjects who really need to lose weight.

Aldosterone contributes to blood pressure variance and to likelihood of hypertension in normal-weight and overweight African Americans

BACKGROUND

Hypertension and obesity are highly prevalent among African Americans (AAs). We have previously reported that both plasma aldosterone (PA) and body mass index (BMI) are higher in hypertensive than in normotensive AAs. This study evaluates the relative contributions of adiposity and PA to hypertension in AAs.

METHODS

A total of 466 AAs (50% hypertensive, 51% women) were evaluated in a Clinical Research Center by stratifying them into three subgroups based on BMI (normal weight, overweight, and obese). Anthropometric measurements, ambulatory blood pressure (BP), fasting glucose, insulin, 24-h urine sodium and potassium, creatinine clearance, standing PA and plasma renin activity (PRA) were measured. Insulin resistance was estimated by the homeostasis model assessment.

RESULTS

Compared to normotensives, hypertensives had higher BMI, waist circumference (WC), and were more insulin resistant (P < or = 0.01). When stratified by BMI, hypertensives in each BMI strata had higher PA (P < or = 0.05) and lower PRA (P < or = 0.01) compared to normotensives. Compared to normotensives, WC was greater in overweight and obese hypertensives, but not in normal-weight hypertensives. In the overall sample, age, WC, PA, and PRA were the major contributors to BP variance and to hypertension. Among normal-weight subjects, PA and PRA significantly predicted BP and the odds ratio for hypertension, whereas WC had no predictive value.

CONCLUSIONS

PA, but not WC, is associated with BP and likelihood of hypertension in normal-weight AAs, whereas both WC and PA are predictive of hypertension in overweight and obese individuals. This suggests that aldosterone antagonists may be useful for the treatment of hypertension among AAs, regardless of BMI.