Insulin hypersecretion: a distinctive feature between essential and secondary hypertension

High blood pressure mediated the effect of fasting insulin level on nonalcoholic fatty liver disease risk: A Mendelian randomization study

Objective

The interactions between fasting insulin levels, high blood pressure and nonalcoholic fatty liver disease (NAFLD) are still unclear. We examined the causal mechanisms between these three cardiometabolic traits using Mendelian randomization (MR) approach by utilizing genetic instruments.

Methods

Three different genome-wide association studies resources of European ancestry were utilized for the present study. Two-sample MRs were used to assess causal effects between fasting insulin levels, high blood pressure and NAFLD. Multivariate MR was used to calculate the mediating effect. The inverse variance-weighted method was used as the main analysis method.

Results

Our study confirmed a causal effect of fasting insulin levels (IVW-OR = 9.54, P = 0.001) and high blood pressure (IVW-OR = 3.926, P = 0.005) on NAFLD risk. And fasting insulin level was positively casually associated with high blood pressure risk (IVW-OR = 1.170, P < 0.001). However, the impact of high blood pressure on fasting insulin levels was still uncertain because of the presence of horizontal pleiotropy. Reverse MR showed NAFLD had a positive correlation with fasting insulin levels (IVW-OR = 1.010, P < 0.001) and a negative causal effect on high blood pressure risk (IVW-OR = 0.997, P = 0.037). Combined the multivariate MR result revealed high blood pressure partially mediated the contribution of fasting insulin level to NAFLD risk (proportion mediated: 9.091%).

Conclusions

Our study suggests there is a bidirectional causal relationship between fasting insulin levels and NAFLD. High blood pressure seems to play a mediating role in the development of NAFLD caused by changes in fasting insulin levels. However, it is uncertain whether high blood pressure is a mediator between NAFLD and the risk of fasting insulin level.

Insulin Resistance and High Blood Pressure: Mechanistic Insight on the Role of the Kidney

The metabolic effects of insulin predominate in skeletal muscle, fat, and liver where the hormone binds to its receptor, thereby priming a series of cell-specific and biochemically diverse intracellular mechanisms. In the presence of a good secretory reserve in the pancreatic islets, a decrease in insulin sensitivity in the metabolic target tissues leads to compensatory hyperinsulinemia. A large body of evidence obtained in clinical and experimental studies indicates that insulin resistance and the related hyperinsulinemia are causally involved in some forms of arterial hypertension. Much of this involvement can be ascribed to the impact of insulin on renal sodium transport, although additional mechanisms might be involved. Solid evidence indicates that insulin causes sodium and water retention, and both endogenous and exogenous hyperinsulinemia have been correlated to increased blood pressure. Although important information was gathered on the cellular mechanisms that are triggered by insulin in metabolic tissues and on their abnormalities, knowledge of the insulin-related mechanisms possibly involved in blood pressure regulation is limited. In this review, we summarize the current understanding of the cellular mechanisms that are involved in the pro-hypertensive actions of insulin, focusing on the contribution of insulin to the renal regulation of sodium balance and body fluids.

Differential roles of FOXO transcription factors on insulin action in brown and white adipose tissue

Insulin and IGF-1 are essential for adipocyte differentiation and function. Mice lacking insulin and IGF-1 receptors in fat (FIGIR-KO, fat-specific IGF-1 receptor and insulin receptor-KO) exhibit complete loss of white and brown adipose tissue (WAT and BAT), glucose intolerance, insulin resistance, hepatosteatosis, and cold intolerance. To determine the role of FOXO transcription factors in the altered adipose phenotype, we generated FIGIR-KO mice with fat-specific KO of fat-expressed Foxos [Foxo1, Foxo3, Foxo4] (F-Quint-KO). Unlike FIGIR-KO mice, F-Quint-KO mice had normal BAT, glucose tolerance, insulin-regulated hepatic glucose production, and cold tolerance. However, loss of FOXOs only partially rescued subcutaneous WAT and hepatosteatosis, did not rescue perigonadal WAT or systemic insulin resistance, and led to even more marked hyperinsulinemia. Thus, FOXOs play different roles in insulin/IGF-1 action in different adipose depots, being most important in BAT, followed by subcutaneous WAT and then by visceral WAT. Disruption of FOXOs in fat also led to a reversal of insulin resistance in liver, but not in skeletal muscle, and an exacerbation of hyperinsulinemia. Thus, adipose FOXOs play a unique role in regulating crosstalk between adipose depots, liver, and β cells.

Insulin sensitivity and pancreatic β-cell function in patients with primary aldosteronism

BACKGROUND

Primary aldosteronism (PA) is associated with an increased risk for dysglycemia. However, the effects of hyperaldosteronism on insulin sensitivity and β-cell function are unclear.

METHODS

Using a cross-sectional study design, we assessed insulin sensitivity and pancreatic β-cell function from an oral glucose tolerance test (OGTT) in patients from two cohorts: subjects with PA (n = 21) and essential hypertension control (EHC) subjects (n = 22). Age, sex, BMI, and mean arterial pressure adjusted measures of insulin sensitivity and β-cell function were compared between the groups.

RESULTS

PA individuals were less insulin sensitive compared to EHC subjects (Quantitative insulin sensitivity check index [QUICKI]: 0.340 ± 0.006 vs. 0.374 ± 0.013, p < 0.001; Matsuda index: 4.14 ± 0.49 vs. 7.87 ± 1.42, p < 0.001; S_I: 11.45 ± 4.85 vs. 21.23 ± 6.11 dL/kg/min per μU/mL, p = 0.02). The hepatic insulin resistance index (HIRI) was higher in PA subjects (PA: 5.61 ± 1.01 vs. EHC: 4.13 ± 0.61, p = 0.002). The insulinogenic index (IGI), an index of β-cell function was higher in the PA cohort (PA: 1.49 ± 0.27 vs. 1.11 ± 0.21 μU/mL/mg/dL, p = 0.03). However, the oral disposition index (DI) was similar between the groups (PA: 4.77 ± 0.73 vs. EHC: 5.46 ± 0.85, p = 0.42), which likely accounts for the similar glucose tolerance between the two cohorts, despite lower sensitivity.

CONCLUSIONS

In summary, insulin sensitivity is significantly lower in PA with an appropriately compensated β-cell function. These results suggest that excess aldosterone and/or other steroids in the context of PA may negatively affect insulin action without adversely impacting β-cell function.

Genetic variation of SORBS1 gene is associated with glucose homeostasis and age at onset of diabetes: A SAPPHIRe Cohort Study

The SORBS1 gene plays an important role in insulin signaling. We aimed to examine whether common single-nucleotide polymorphisms (SNPs) of SORBS1 are associated with prevalence and incidence of diabetes, age at onset of diabetes, and the related traits of glucose homeostasis. A total of 1135 siblings from 492 ethnic Chinese families were recruited at baseline, and 630 were followed up for 5.19 ± 0.96 years. Nine SNPs including rs7081076, rs2281939, rs3818540, rs2274490, rs61739184, rs726176, rs2296966, rs17849148, and rs3193970 were genotyped and examined. To deal with correlated data of subjects within the same families, the generalized estimating equations approach was applied throughout all association analyses. The GG genotype of rs2281939 was associated with a higher risk of diabetes at baseline, an earlier onset of diabetes, and higher steady-state plasma glucose levels in the modified insulin suppression test. The minor allele T of rs2296966 was associated with higher prevalence and incidence of diabetes, an earlier onset of diabetes, and higher 2-h glucose during oral glucose tolerance test. These two SNPs revealed independent associations with age of diabetes onset as well as risk of diabetes at baseline. These findings supported that SORBS1 gene participates in the pathogenesis of diabetes.

Genetic Variation in the Human SORBS1 Gene is Associated With Blood Pressure Regulation and Age at Onset of Hypertension: A SAPPHIRe Cohort Study

Essential hypertension is a complex disease involving multiple genetic and environmental factors. A human gene containing a sorbin homology domain and 3 SH3 domains in the C-terminal region, termed SORBS1, plays a significant role in insulin signaling. We previously found a significant association between the T228A polymorphism and insulin resistance, obesity, and type 2 diabetes. It has been hypothesized that a set of genes responsible for insulin resistance may be closely linked with genes susceptible to the development of hypertension. Identification of insulin resistance-related genetic factors may, therefore, enhance our understanding of essential hypertension. This study aimed to examine whether common SORBS1 genetic variations are associated with blood pressure and age at onset of hypertension in an ethnic Chinese cohort.We genotyped 9 common tagged single nucleotide polymorphisms of the SORBS1 gene in 1136 subjects of Chinese origin from the Stanford Asia-Pacific Program for Hypertension and Insulin Resistance family study. Blood pressure was measured upon enrolment. The associations of the SORBS1 single nucleotide polymorphisms with blood pressure and the presence of hypertension were analyzed with a generalized estimating equation model. We used the false-discovery rate measure Q value with a cutoff <0.1 to adjust for multiple comparisons. In the Cox regression analysis for hypertension-free survival, a robust sandwich variance estimator was used to deal with the within-family correlations with age at onset of hypertension. Gender, body mass index, and antihypertension medication were adjustment covariates in the Cox regression analysis.In this study, genetic variants of rs2281939 and rs2274490 were significantly associated with both systolic and diastolic blood pressure. A genetic variant of rs2274490 was also significantly associated with the presence of hypertension. Furthermore, genetic variants of rs2281939 and rs2274490 were associated with age at onset of hypertension after adjustment for gender, body mass index, and antihypertension medication.In conclusion, we provide evidence for an association between common SORBS1 genetic variations and blood pressure, presence of hypertension, and age at onset of hypertension. The biological mechanism of genetic variation associated with blood pressure regulation needs further investigation.

Association of Post-Saline Load Plasma Aldosterone Levels With Left Ventricular Hypertrophy in Primary Hypertension

BACKGROUND

Left ventricular hypertrophy (LVH) is an independent risk factor for cardiovascular morbidity in hypertension. Current evidence suggests a contribution to LVH of plasma aldosterone levels that are inappropriately elevated for the salt status. The aim of this study was to investigate whether inappropriate modulation of aldosterone production by a saline load is associated with left ventricular (LV) mass in hypertensive patients.

METHODS

In 90 hypertensive patients free of clinically relevant cardiovascular complications in whom secondary forms of hypertension were ruled out, we performed a standard intravenous saline load (0.9% NaCl, 2 l in 4 hours) with measurement of plasma aldosterone and active renin at baseline and end of infusion. Bi-dimensional echocardiography was performed for the assessment of cardiac morphology and function.

RESULTS

LVH was present in 19% of patients who had significantly worse renal function and higher body mass, blood pressure, and plasma aldosterone levels measured both at baseline and after the saline load than patients without LVH. LV mass was directly related to age, body mass, systolic blood pressure, duration of hypertension, baseline, and post-saline load plasma aldosterone levels and inversely to glomerular filtration. Multivariate regression analysis showed independent correlation of LV mass with body mass, systolic blood pressure, and plasma aldosterone levels measured after intravenous saline load, but not at baseline.

CONCLUSIONS

In patients with hypertension, aldosterone levels measured after intravenous saline load are related to LV mass independent of age, body mass, and blood pressure, suggesting that limited ability of salt to modulate aldosterone production could contribute to LVH.

Carotid artery stiffness is related to hyperinsulinemia and insulin-resistance in middle-aged, non-diabetic hypertensive patients

BACKGROUND AND AIMS

Glycometabolic abnormalities are frequently found in hypertension and could affect the mechanical properties of carotid arteries. The aim of the study was to investigate the relationship of glucose tolerance, plasma insulin, and insulin sensitivity with carotid distensibility in middle-aged, non-diabetic hypertensive patients free of cardiac and vascular complications.

METHOD AND RESULTS

In 93 patients with grade 1-2, uncomplicated, primary hypertension and 68 matched normotensive controls we measured plasma glucose and insulin at fast and after an oral glucose load (OGTT), calculated the HOMA-index as a marker of insulin sensitivity, and assessed distensibility of common carotid arteries by B-mode ultrasonography. Hypertensive patients were hyperinsulinemic and insulin-resistant as compared to normotensive controls. Hypertensive patients with impaired fasting glucose and/or impaired glucose tolerance had comparable distensibility of carotid arteries. Patients with decreased carotid distensibility were older and had higher body mass, fasting and post-OGTT plasma insulin, HOMA-index, and carotid IMT than the remaining patients, but no differences in glycated hemoglobin, and fasting or post-OGTT plasma glucose. Carotid coefficient of distensibility was inversely related and β-stiffness directly related with fasting and post-OGTT plasma insulin, and HOMA-index. Multivariate logistic regression showed that age and post-OGTT plasma insulin levels predicted carotid artery stiffening independent of body mass index, sex, blood pressure, and plasma glucose levels.

CONCLUSIONS

The study demonstrates that decreased insulin sensitivity and the related hyperinsulinemia but not hyperglycemia could contribute to carotid artery stiffening in middle-aged, non-diabetic hypertensive patients free of cardiovascular complications.

Elevated Homocysteine Levels Are Associated With the Metabolic Syndrome and Cardiovascular Events in Hypertensive Patients

BACKGROUND

Hyperhomocysteinemia and the metabolic syndrome are established cardiovascular risk factors and are frequently associated with hypertension. The relationship of plasma homocysteine (Hcy) with the metabolic syndrome and insulin resistance, however, is debated and studies in hypertensive patients are limited. In this study, we have investigated the association of Hcy with the metabolic syndrome and cerebro- cardiovascular events in hypertension.

METHODS

In 562 essential hypertensive patients who underwent accurate assessment of fasting and postload glucose metabolism, insulin sensitivity, and renal function, we measured plasma levels of Hcy, vitamin B12, folate, and fibrinogen and assessed the prevalence of the metabolic syndrome and of coronary heart and cerebrovascular disease (CVD).

RESULTS

Patients with the metabolic syndrome had significantly higher plasma Hcy levels. After correction for covariates, increasing Hcy levels were associated with an increasing prevalence of the metabolic syndrome, coronary heart disease, and CVD. Plasma Hcy was directly correlated with age, waist circumference, fasting glucose, triglyceride, uric acid, and fibrinogen levels, and homeostatic model assessment index and inversely with creatinine clearance and high-density lipoprotein cholesterol, vitamin B12, and folate levels. Logistic regression analysis showed an independent association of Hcy levels with age, male gender, vitamin B12 and folate levels, and the metabolic syndrome. Logistic regression indicated also an independent association of Hcy with cerebro-cardiovascular disease that was independent of the metabolic syndrome.

CONCLUSIONS

Elevated plasma Hcy is associated with the metabolic syndrome in hypertensive patients. Prevalence of events increases with increasing plasma Hcy levels suggesting a contribution of Hcy to cerebro-cardiovascular diseases in these patients.

Subclinical carotid artery disease and plasma homocysteine levels in patients with hypertension

Information on the association between homocysteine (Hcy) levels and subclinical carotid artery disease is limited. We investigated the relationship of plasma Hcy concentration with carotid artery plaques and intima-media thickness (IMT) in patients with hypertension. In 486 essential hypertensive patients who underwent ultrasound examination of the carotid arteries, we measured plasma levels of Hcy, vitamin B12, folate, and C-reactive protein. Plaques were detected in 34% of the study patients. Plasma Hcy levels were significantly greater in hypertensive patients with evidence of carotid plaques than patients without carotid plaques. Carotid IMT progressively increased across quartiles of plasma Hcy levels. Multivariate regression showed that carotid IMT was independently related with age, blood pressure, C-reactive protein, and Hcy levels. In a logistic regression, age, blood pressure, triglyceride, and Hcy independently predicted the presence of carotid plaques. Thus, elevated plasma Hcy levels are associated with asymptomatic carotid disease in hypertensive patients suggesting a role of Hcy in the development and progression of carotid atherosclerosis in these patients.

Relationships of plasma lipoprotein(a) levels with insulin resistance in hypertensive patients

BACKGROUND

Lipoprotein(a) [Lp(a)] is an emergent cardiovascular risk factor that is related to the presence and severity of cardiovascular damage in hypertensive patients. In these patients, insulin resistance is frequently detected but its relationship with plasma Lp(a) is not clear. The aim of this study was to examine the relationships between Lp(a) and variables of glucose metabolism in hypertension.

METHODS

In 527 consecutive, non-diabetic, middle-aged hypertensive patients we measured anthropometric indexes, 24-hour creatinine clearance, lipid profile including Lp(a) levels, fasting glucose, insulin and C-peptide, and calculated the Homeostatic Model Assessment (HOMA) index.

RESULTS

Lp(a) levels were significantly and progressively lower with increasing HOMA-index values. Lp(a) was inversely related to fasting glucose, insulin, and C-peptide, HOMA-index, and creatinine clearance and directly related to LDL-cholesterol. Multiple regression analysis adjusted for age, sex, body mass index, blood pressure, smoking habit, alcohol intake, renal function, lipid profile, history of cardiovascular events, and drug use showed that HOMA-index and creatinine clearance were inversely and independently associated to Lp(a) levels.

CONCLUSIONS

Insulin resistance and higher fasting insulin levels are associated with lower plasma Lp(a) in hypertensive patients. This association might be relevant in the assessment of cardiovascular risk in these patients.

Uricaemia and left ventricular mass in hypertensive patients

BACKGROUND

Both hyperuricaemia and left ventricular (LV) hypertrophy are associated with the metabolic syndrome and increased cardiovascular risk. The relationship between uric acid levels and left ventricular mass in hypertension, however, is unclear. In this study, we have investigated this relationship in hypertensive patients without the metabolic syndrome.

MATERIALS AND METHODS

In a cross-sectional study, 367 nondiabetic, essential hypertensive patients (age 52 ± 14; 194 males and 173 females) free of clinically relevant cardiovascular complications and without the metabolic syndrome were consecutively recruited at a university hypertension clinic. In these patients, we measured plasma levels of uric acid, lipids, glucose and insulin at fast and after an oral glucose load (OGTT), renal function and performed both conventional and tissue Doppler echocardiography.

RESULTS

Hypertensive patients with LV hypertrophy had higher uric acid levels and greater prevalence of hyperuricemia than patients with normal left ventricular mass. Uric acid levels were directly related with fasting and post-OGTT plasma insulin and with the HOMA index and inversely with 24-h creatinine clearance. Uric acid was also significantly and directly related with the left ventricular mass and multivariate regression analysis showed that this relationship was independent from components of the metabolic syndrome and renal function in women, but not in men.

CONCLUSIONS

Elevated uric acid levels are independently related to the left ventricular mass in hypertensive women without the metabolic syndrome. In these patients with a low cardiovascular risk profile, uric acid might contribute to the development of subclinical cardiac damage.

Insulin transcriptionally regulates argininosuccinate synthase to maintain vascular endothelial function

Diminished vascular endothelial cell nitric oxide (NO) production is a major factor in the complex pathogenesis of diabetes mellitus. In this report, we demonstrate that insulin not only maintains endothelial NO production through regulation of endothelial nitric oxide synthase (eNOS), but also via the regulation of argininosuccinate synthase (AS), which is the rate-limiting step of the citrulline-NO cycle. Using serum starved, cultured vascular endothelial cells, we show that insulin up-regulates AS and eNOS transcription to support NO production. Moreover, we show that insulin enhances NO production in response to physiological cues such as bradykinin. To translate these results to an in vivo model, we show that AS transcription is diminished in coronary endothelial cells isolated from rats with streptozotocin (STZ)-induced diabetes. Importantly, we demonstrate restoration of AS and eNOS transcription by insulin treatment in STZ-diabetic rats, and show that this restoration was accompanied by improved endothelial function as measured by endothelium-dependent vasorelaxation. Overall, this report demonstrates, both in cell culture and whole animal studies, that insulin maintains vascular function, in part, through the maintenance of AS transcription, thus ensuring an adequate supply of arginine to maintain vascular endothelial response to physiological cues.

Hypertension in obesity

Obesity and HTN are on the rise in the world. HTN seems to be the most common obesity-related health problem and visceral obesity seems to be the major culprit. Unfortunately, only 31% of hypertensives are treated to goal. This translates into an increased incidence of CVD and related morbidity and mortality. Several mechanisms have been postulated as the causes of obesity-related HTN. Activation of the RAAS, SNS, insulin resistance, leptin, adiponectin, dysfunctional fat, FFA, resistin, 11 Beta dehydrogenase, renal structural and hemodynamic changes, and OSA are some of the abnormalities in obesity-related HTN. Many of these factors are interrelated. Treatment of obesity should begin with weight loss via lifestyle modifications, medications, or bariatric surgery. According to the mechanisms of obesity-related HTN, it seems that drugs that blockade the RAAS and target the SNS should be ideal for treatment. There is not much evidence in the literature that one drug is better than another in controlling obesity-related HTN. There have only been a few studies specifically targeting the obese hypertensive patient, but recent trials that emphasize the importance of BP control have enrolled both overweight and obese subjects. Until we have further studies with more in-depth information about the mechanisms of obesity-related HTN and what the targeted treatment should be, the most important factor necessary to control the obesity-related HTN pandemic and its CVD and CKD consequences is to prevent and treat obesity and to treat HTN to goal.

Comparison of clinical outcomes following acute myocardial infarctions in hypertensive patients with or without diabetes

Background and Objectives

It is thought that patients with diabetes mellitus (DM) have a poor prognosis after an acute myocardial infarction (AMI), but the effect of diabetes on the outcomes of hypertensive patients with AMIs has not been elucidated in the Korean population. The aim of this study was to investigate the effects of diabetes on long-term clinical outcomes following AMIs in patients with hypertension.

Subjects and Methods

Using data from the Korea Acute Myocardial Infarction Registry (November 2005 to December 2006), 2,233 hypertensive patients with AMIs were grouped as follows based on the presence of DM: group I, diabetic hypertension (n=892, 544 men, mean age=66.2±10.9 years); and group II, non-diabetic hypertension (n=1341, 938 men, mean age=63.9±12.8 years). The primary study outcomes included in-hospital death and major adverse cardiac events (MACE; cardiac death, myocardial infarction (MI), repeat percutaneous coronary intervention, and coronary artery bypass surgery) at the 1 year follow-up.

Results

Hypertensive patients with DM were older and more likely to be women. The diabetic group had lower blood pressure (p<0.001), a lower left ventricular ejection fraction (p<0.001), a more severe degree of heart failure (p<0.001), a longer duration of coronary care unit admission (p<0.001), and a higher incidence of hyperlipidemia (p=0.007). The N-terminal pro-brain natriuretic peptide level (4602.5±8710.6 pg/mL vs. 2320.8±5837.9 pg/mL, p<0.001) was higher and the creatinine clearance (62.4±29.9 mL/min vs. 73.0±40.8 mL/min, p<0.001) was lower in the diabetic group than the non-diabetic group. Coronary angiographic findings revealed more frequent involvement of the left main stem (p=0.002) and multiple vessels (p<0.001) in the diabetic group. The rate of in-hospital death was higher in the diabetic group (p<0.001). During follow-up, the rates of composite MACE at 1 month, 6 months, and 12 months were higher in the diabetic group (p<0.001).

Conclusion

In hypertensive patients with AMI, DM was associated with worse clinical and angiographic features, with a higher risk of development of severe heart failure, and an increased risk of MACE on long-term clinical follow-up.

Hypertension in obesity

Hypertension and obesity are major components of the cardiometabolic syndrome and are both on the rise worldwide, with enormous consequences on global health and the economy. The relationship between hypertension and obesity is multifaceted; the etiology is complex and it is not well elucidated. This article, reviews the current knowledge on obesity-related hypertension. Further understanding of the underlying mechanisms of this epidemic will be important in devising future treatment avenues.

Insulin resistance and hyperinsulinemia are related to plasma aldosterone levels in hypertensive patients

OBJECTIVE

An association between aldosterone and insulin resistance has been demonstrated in obesity and primary aldosteronism and in blacks with the metabolic syndrome. The aim of this study was to evaluate the relationship of plasma aldosterone with insulin sensitivity in white subjects.

RESEARCH DESIGN AND METHODS

In 356 patients with essential hypertension and 102 normotensive control subjects of comparable age and BMI, we measured, after discontinuation of treatment, plasma active renin, aldosterone, cortisol, glucose, insulin, and C-peptide levels and calculated markers of insulin sensitivity. Direct assessment of insulin sensitivity was obtained in a subset of 64 hypertensive patients by a hyperinsulinemic clamp.

RESULTS

Hypertensive patients had significantly greater fasting plasma insulin and C-peptide concentrations and homeostasis model assessment (HOMA) indexes than normotensive control subjects. A positive association with increasing plasma aldosterone concentrations was demonstrated for plasma glucose, insulin, C-peptides, and HOMA. Assessment of insulin sensitivity by clamp showed a significant decrease of the metabolic clearance rate of glucose with increasing aldosterone levels. Significant correlations were found between plasma aldosterone, plasma insulin, and C-peptide levels, HOMA, and glucose metabolic clearance rate. Blood pressure and plasma potassium, plasma cortisol, and renin levels, but not BMI, were also directly correlated with plasma aldosterone. Multiple regression analysis showed that HOMA, together with plasma potassium, cortisol, and renin levels, was independently correlated with plasma aldosterone.

CONCLUSIONS

This study demonstrates a direct relationship between aldosterone, insulin resistance, and hyperinsulinemia in white subjects. In patients with hypertension, this relationship might contribute to maintenance of high blood pressure and increased cardiovascular risk.

Insulin resistance, hyperinsulinemia, and hypertension: an epidemiologic approach

During the past 2 decades, numerous experimental studies have provided solid evidence for the existence of several mechanisms connecting insulin resistance and hyperinsulinemia with blood pressure elevation, within the context of the cardiometabolic syndrome. In parallel, several groups have attempted to examine these associations from an epidemiologic perspective, but relevant findings were less consistent and not extensively discussed. Hyperinsulinemia has been associated with high blood pressure levels and hypertension development in cross-sectional, case-control, and prospective cohort studies. An association between insulin resistance and hypertension is also evident in existing studies, but prospective data on this relation are limited. Moreover, most of the evidence supporting close associations between these factors derives from Caucasian and Japanese populations, whereas data in other populations are not in agreement. This review summarizes and evaluates the relevant epidemiologic evidence to elucidate an important aspect of the relationship between hypertension and the cardiometabolic syndrome.

Angiotensin II-induced NADPH oxidase activation impairs insulin signaling in skeletal muscle cells

The renin-angiotensin system (RAS) and reactive oxygen species (ROS) have been implicated in the development of insulin resistance and its related complications. There is also evidence that angiotensin II (Ang II)-induced generation of ROS contributes to the development of insulin resistance in skeletal muscle, although the precise mechanisms remain unknown. In the present study, we found that Ang II markedly enhanced NADPH oxidase activity and consequent ROS generation in L6 myotubes. These effects were blocked by the angiotensin II type 1 receptor blocker losartan, and by the NADPH oxidase inhibitor apocynin. Ang II also promoted the translocation of NADPH oxidase cytosolic subunits p47phox and p67phox to the plasma membrane within 15 min. Furthermore, Ang II abolished insulin-induced tyrosine phosphorylation of insulin receptor substrate 1 (IRS1), activation of protein kinase B (Akt), and glucose transporter-4 (GLUT4) translocation to the plasma membrane, which was reversed by pretreating myotubes with losartan or apocynin. Finally, small interfering RNA (siRNA)-specific gene silencing targeted specifically against p47phox (p47siRNA), in both L6 and primary myotubes, reduced the cognate protein expression, decreased NADPH oxidase activity, restored Ang II-impaired IRS1 and Akt activation as well as GLUT4 translocation by insulin. These results suggest a pivotal role for NADPH oxidase activation and ROS generation in Ang II-induced inhibition of insulin signaling in skeletal muscle cells.

Insulin sensitivity in patients with primary aldosteronism: a follow-up study

CONTEXT

The relationship between aldosterone and glucose metabolism is poorly understood, and there is substantial disparity among findings of studies that have examined glucose tolerance and insulin sensitivity in patients with primary aldosteronism.

OBJECTIVE

The objective of the study was to determine the outcome of glucose tolerance and insulin sensitivity in patients with primary aldosteronism after treatment.

DESIGN

This was a prospective study of patients who received a diagnosis of primary aldosteronism and were followed up for an average period of 5.7 yr (range, 3-9 yr).

SETTING

The study was conducted at a university referral center.

PATIENTS

A consecutive sample of 47 patients with tumoral or idiopathic aldosteronism was followed up after either surgical or medical treatment. Patients with primary aldosteronism were compared with 247 patients with essential hypertension with the same severity and duration of disease and 102 normotensive subjects.

MAIN OUTCOME MEASURES

Short- and long-term changes in glucose tolerance and insulin sensitivity were measured.

RESULTS

After adjustment for age, gender, and body mass index, patients with primary aldosteronism had greater homeostasis model assessment index (P < 0.05) and plasma insulin response to an oral glucose load (P < 0.05) and lower quantitative insulin sensitivity check index (P < 0.01) than normotensive controls. Changes in insulin sensitivity were significantly greater in essential hypertension than primary aldosteronism, and this difference was confirmed by assessment with the hyperinsulinemic-euglycemic clamp (P < 0.01). Treatment of primary aldosteronism decreased blood pressure significantly, and during the initial 6 months of follow-up, parameters of insulin sensitivity were restored to normal. Analysis of subsequent follow-up showed nonsignificant changes in glucose metabolism parameters in both adrenalectomized and spironolactone-treated patients.

CONCLUSIONS

Insulin resistance is present in patients with tumoral and idiopathic aldosteronism, but the defect appears less severe than in patients with essential hypertension. Treatment with surgery or aldosterone antagonists restores rapidly and persistently normal sensitivity to insulin.

Insulin resistance in spontaneously hypertensive rats is associated with endothelial dysfunction characterized by imbalance between NO and ET-1 production

Insulin stimulates production of NO in vascular endothelium via activation of phosphatidylinositol (PI) 3-kinase, Akt, and endothelial NO synthase. We hypothesized that insulin resistance may cause imbalance between endothelial vasodilators and vasoconstrictors (e.g., NO and ET-1), leading to hypertension. Twelve-week-old male spontaneously hypertensive rats (SHR) were hypertensive and insulin resistant compared with control Wistar-Kyoto (WKY) rats (systolic blood pressure 202 +/- 11 vs. 132 +/- 10 mmHg; fasting plasma insulin 5 +/- 1 vs. 0.9 +/- 0.1 ng/ml; P < 0.001). In WKY rats, insulin stimulated dose-dependent relaxation of mesenteric arteries precontracted with norepinephrine (NE) ex vivo. This depended on intact endothelium and was blocked by genistein, wortmannin, or N(omega)-nitro-l-arginine methyl ester (inhibitors of tyrosine kinase, PI3-kinase, and NO synthases, respectively). Vasodilation in response to insulin (but not ACh) was impaired by 20% in SHR (vs. WKY, P < 0.005). Preincubation of arteries with insulin significantly reduced the contractile effect of NE by 20% in WKY but not SHR rats. In SHR, the effect of insulin to reduce NE-mediated vasoconstriction became evident when insulin pretreatment was accompanied by ET-1 receptor blockade (BQ-123, BQ-788). Similar results were observed during treatment with the MEK inhibitor PD-98059. In addition, insulin-stimulated secretion of ET-1 from primary endothelial cells was significantly reduced by pretreatment of cells with PD-98059 (but not wortmannin). We conclude that insulin resistance in SHR is accompanied by endothelial dysfunction in mesenteric vessels with impaired PI3-kinase-dependent NO production and enhanced MAPK-dependent ET-1 secretion. These results may reflect pathophysiology in other vascular beds that directly contribute to elevated peripheral vascular resistance and hypertension.

Diabetes, hypertension, and cardiovascular derangements: Pathophysiology and management

Hypertension frequently coexists with diabetes mellitus, occurring twice as frequently in diabetic as in nondiabetic persons. It accounts for up to 75% of added cardiovascular disease (CVD) risk in people with diabetes, contributing significantly to the overall morbidity and mortality in this high-risk population. Patients with hypertension are two times more prone to have diabetes than are normotensive persons. Hypertension substantially increases the risk for coronary heart disease (CHD), stroke, retinopathy, and nephropathy. In patients with type 2 diabetes, hypertension usually clusters with the other components of the cardiometabolic syndrome, such as microalbuminuria, central obesity, insulin resistance, dyslipidemia, hypercoagulation, increased inflammation, and left ventricular hypertrophy (LVH). In type 1 diabetes, hypertension often occurs subsequent to the development of diabetic nephropathy. Hypertension in people with diabetes is characterized by volume expansion, increased salt sensitivity, isolated systolic blood pressure (BP) elevation, loss of the nocturnal dipping of BP and pulse, and increased propensity toward orthostatic hypotension and albuminuria. Among the treatment strategies tested in hypertensive diabetic persons, low-density lipoprotein (LDL)-cholesterol lowering to less than 100 mg/dL and aggressive BP control to less than 130/80 mm Hg have proven effective in CVD risk reduction. The combination of two or more drugs is usually necessary to achieve the target BP.

Insulin and insulin resistance: impact on blood pressure and cardiovascular disease

Cardiovascular disease is a major cause of mortality in individuals with diabetes. Many factors, including hypertension, contribute to the high prevalence of CVD in this population. Hypertension occurs approximately twice as frequently in patients with diabetes compared with patients without diabetes. Conversely, recent data suggest that hypertensive persons are more likely to develop diabetes than normotensive persons. In addition, up to 75% of CVD in patients with diabetes may be attributed to hypertension, leading to recommendations for more aggressive blood pressure control (ie, < 130/85 mm Hg) in persons with coexistent diabetes and hypertension. Increasing obesity further contributes to both diabetes and hypertension and significantly increases CVD morbidity and mortality. Other important risk factors for CVD in these patients include atherosclerosis, dyslipidemia, microalbuminuria, endothelial dysfunction, platelet hyperaggregability, coagulation abnormalities, and diabetic cardiomyopathy. The current knowledge regarding these risk factors has been reviewed, placing special emphasis on the metabolic syndrome, hypertension, microalbuminuria, and the role of obesity in these disorders. Although not discussed in detail, it is acknowledged that both hygienic measures (weight loss and aerobic exercise) and treatment strategies that include aspirin, statins, INS sensitizers, and antihypertensive agents that reduce renin-angiotensin-aldosterone system activity have been shown to reduce inflammation, coagulation abnormalities, endothelial function, proteinuria, and in some cases reduce CVD and renal disease progression. Additional therapeutic agents are currently being developed specifically to improve INS sensitivity and other CVD risk factors that are components of the cardiometabolic syndrome.

Insulin increases angiotensinogen expression in human abdominal subcutaneous adipocytes

The renin-angiotensin system is an important regulator of blood pressure, and blockade of this system improves blood pressure in obesity and type 2 diabetes. Recently, components of the system have been described in adipose tissue. However, to date no study has investigated the influence of varying insulin concentrations on angiotensinogen (AGT) protein expression in human subcutaneous abdominal fat. Isolated subcutaneous adipocytes were treated with insulin (1-1000 nm) for 48 h. As part of the studies, a novel AGT antibody was developed and validated by Western blotting and immunohistochemistry. Western blotting was performed on the protein extracted from the adipocytes treated with insulin to determine AGT expression. Increasing doses of insulin raised AGT protein expression in a dose-dependent manner (control 1.0 +/- 0.0 (mean +/- s.e.) - protein expression standardized relative to control; 1 nm insulin: 2.64 +/- 0.0.32 upward arrow ***; 100 nm insulin: 4.37 +/- 0.57 upward arrow ***; 1000 nm insulin: 6.50 +/- 0.97 upward arrow ***; ***p < 0.001, n = 3). In conclusion, increasing insulin doses stimulates AGT production. In this study, protein analysis suggests that hyperinsulinaemia may be an important factor in obesity-related hypertension.

Insulin resistance syndrome in children : pathophysiology and potential management strategies

The simultaneous presence of various cardiovascular risk factors in the same individual is not rare, even in the pediatric age group. The clustering of risk factors can be termed insulin resistance syndrome (IRS) because of the putative central role of tissue insulin insensitivity in the background of the inter-related metabolic disturbances. Fasting hyperinsulinemia, impaired glucose tolerance, dyslipidemia, and hypertension are considered to represent the basic abnormalities of IRS. The most prevalent related disturbances are increased plasma levels of plasminogen activator inhibitor-1, fibrinogen, uric acid, homocysteine, and C-reactive protein, as well as visceral adiposity, microalbuminuria, disturbed essential fatty acid metabolism, low availability of lipid-soluble antioxidant vitamins, and enhanced expression of tumor necrosis factor-alpha in adipose tissues. Certain genetic abnormalities have been associated with IRS, but explain only a small part of the variability in insulin resistance. The exact prevalence of IRS in children remains to be defined; it was found to be 9% in one survey among children with obesity seeking medical attention. Modification of lifestyle, i.e. reduction of energy intake and enhancement of physical activity, are unquestionable prerequisites for long-term success in the management of IRS. In at least two randomized controlled studies, metformin proved to be clinically effective in increasing insulin sensitivity in hyperinsulinemic, nondiabetic adolescents. Thiazolidinediones have been successfully tested for the treatment of insulin resistance in adults, but not in children as yet. Prevention of the development of IRS in children is obviously of great significance for the health status of the community. However, the efficacy of various preventive approaches should be investigated further in carefully designed controlled trials.

Prevention of type 2 diabetes

Diabetes is a major public health problem that is approaching epidemic proportions in our society and worldwide. Cardiovascular disease is the major cause of morbidity and mortality in people with diabetes. Control of cardiovascular disease risk factors is achieved only in a minority of patients. Given the magnitude of the problem and the seriousness of diabetes complications, prevention appears to be a logical approach to curb the rising prevalence of the disease. Interventions such as lifestyle modifications and the use of metformin and acarbose have been shown in randomized prospective trials to prevent diabetes in high-risk patients. Other interventions are currently being examined in large prospective studies. It is likely that one or a combination of these approaches will make diabetes prevention a reality in the near future.

Serum lipoprotein(a) concentrations and alcohol consumption in hypertension: possible relevance for cardiovascular damage

OBJECTIVES

To evaluate the relationships between alcohol intake and serum lipoprotein(a) [Lp(a)], a powerful predictor of organ damage, in patients with essential hypertension with a wide range of alcohol intake, and to investigate whether the association between alcohol intake and serum Lp(a) concentrations occurs over the entire spectrum of apo(a) phenotypes.

DESIGN

Cross-sectional study of a case series.

SETTING

University medical centre.

PATIENTS

Four hundred and two patients with untreated essential hypertension recruited at a hypertension clinic.

MAIN OUTCOME MEASURES

Serum Lp(a) concentrations, apo(a) isoforms, alcohol consumption, smoking habits and cardiovascular status.

RESULTS

No difference in Lp(a) concentrations was observed between teetotalers and occasional drinkers. Light drinkers (1-20 g/day ethanol), moderate drinkers (21-50 g/day), and heavy drinkers (> 50 g/day) had, respectively, 21, 26 and 57% lower median Lp(a) concentrations than teetotalers and occasional drinkers. Similar findings were obtained when male and female patients were analysed separately. Log Lp(a) concentrations were inversely and independently correlated with alcohol consumption in both men and women with hypertension. The frequency distributions of apo(a) isoforms and liver function parameters were comparable across the different alcohol intake groups. Patients with evidence of cardiovascular damage had greater concentrations of serum Lp(a) and higher frequency of low-molecular weight apo(a) isoforms as compared with patients without such evidence.

CONCLUSIONS

Serum Lp(a) is inversely and dose-dependently related with alcohol intake in patients with hypertension, and this relationship is independent of the size distribution of apo(a) isoforms. Reduction of Lp(a) concentrations by regular consumption of alcohol might favourably affect the atherosclerotic risk profile of patients with hypertension and thereby decrease cardiovascular morbidity.

Abnormalities of glucose metabolism in patients with early renal failure

Abnormalities of glucose metabolism and hyperinsulinemia have been demonstrated in patients with end-stage renal disease and may contribute to the development of atherosclerotic complications in these patients. In the present study, we investigated the stage of renal failure in which abnormalities of glucose metabolism develop and whether these abnormalities were associated with an increased prevalence of cardiovascular events in patients with early renal failure. In 321 untreated essential hypertensive patients, we assessed renal function by measuring 24-h creatinine clearance, urinary protein excretion, and microalbuminuria; we assessed cardiovascular status by clinical and laboratory tests; and we measured plasma glucose, insulin, and C-peptide levels at fasting and after a 75-g oral glucose load. To evaluate insulin sensitivity, a hyperinsulinemic-euglycemic clamp was performed in a subgroup of 104 patients. Patients with creatinine clearance < 30 ml.min(-1).1.73 m(-2), severe hypertension, BMI < 30 kg/m(2), and diabetes or family history of diabetes were excluded. Hypertensive patients were found to be hyperinsulinemic when compared with 92 matched normotensive subjects. Early renal failure (creatinine clearance < 90 ml.min(-1).1.73 m(-2)) caused by hypertensive nephrosclerosis was detected in 116 of 321 patients. Analysis of patients with varying degrees of renal function impairment demonstrated increased plasma glucose and insulin response to oral glucose load, decreased fasting glucose-to-insulin ratio, and reduced sensitivity to insulin only in those patients with creatinine clearance < 50 ml.min(-1).1.73 m(-2). Parameters of glucose metabolism were not correlated with creatinine clearance and microalbuminuria. Prevalence of atherosclerotic cardiovascular events was significantly related to reduction of creatinine clearance, but parameters of glucose metabolism were comparable in patients with and without evidence of atherosclerotic damage. Thus, in patients with hypertensive nephrosclerosis and early impairment of glomerular filtration, alterations of glucose metabolism become evident only when creatinine clearance is < 50 ml.min(-1).1.73 m(-2) and are not related to microalbuminuria and cardiovascular complications.

Relationship of lipoprotein(a) to variables of coagulation in hypertensive subjects

BACKGROUND

Coagulation factors are independent predictors of cardiovascular damage in the general population. The purpose of this study was to investigate the relationships between general cardiovascular risk factors, lipoprotein(a) (Lp(a)), and some hemostatic variables, and to characterize the isoforms of apolipoprotein(a) (apo(a)) in hypertensive subjects.

METHODS

Plasma lipids, apolipoproteins, Lp(a), apo(a) isoforms, fibrinogen, and parameters that directly reflect the coagulation activation were measured in 389 untreated essential hypertensive patients recruited at a hypertension clinic. Hypertensive patients were compared with 323 normotensive controls.

RESULTS

In normotensive subjects, Lp(a) concentrations were significantly correlated with fibrinogen (r = 0.138; P < 0.02) but not D-dimer (r = 0.074; not significant). In hypertensive subjects, log Lp(a) concentrations were significantly correlated with age (r = 0.127; P < 0.02), apo-B (r = 0.128; P < 0.02), plasma fibrinogen (r = 0.193; P < 0.001), and fibrin D-dimer (r = 0.200; P < 0.001) levels, but not with body mass index, blood pressure, cholesterol, triglycerides, apo-AI, prothrombin fragment 1 + 2, and antithrombin III. The relationship of Lp(a) with fibrinogen (male: r = 0.198, P < 0.002; female: r = 0.177, P < 0.01) and D-dimer (male: r = 0.211, P < 0.002; female: r = 0.188, P < 0.01) was significant in both sexes, whereas the relationship of Lp(a) with age and apo-B was found only in males. Multivariate analysis showed that both fibrinogen and D-dimer were independently related with Lp(a). Elevated fibrinogen, D-dimer, and Lp(a) levels were significantly and independently associated with clinical evidence of atherosclerotic disease. Apo(a) phenotypes were analyzed to investigate the genetic background of the relationships between Lp(a) and coagulation parameters. In both hypertensive and normotensive subjects, Lp(a) levels were inversely correlated with apo(a) isoform protein size, whereas fibrinogen and D-dimer concentrations were comparable in patients with apo(a) isoforms of different size.

CONCLUSIONS

The relationship between Lp(a) and clotting variables is significantly stronger in hypertensive than in normotensive subjects, providing a compelling argument for accelerated progression of atherothrombosis in these patients.

Abnormalities of coagulation in hypertensive patients with reduced creatinine clearance

PURPOSE

The prothrombotic state that occurs in uremic patients may increase their cardiovascular risk. We studied hypertensive patients with mild-to-moderate impairment of renal function to determine if they had evidence of abnormalities in the coagulation system.

SUBJECTS AND METHODS

Renal function was assessed in 382 patients with essential hypertension, in whom 24-hour creatinine clearance, urinary protein excretion, and microalbuminuria were measured. We evaluated the function of the coagulation system by measurement of platelet counts, prothrombin time, partial thromboplastin time, and plasma antithrombin III, fibrinogen, D-dimer, and prothrombin fragment 1 + 2 levels.

RESULTS

Impaired renal function, defined as a creatinine clearance of 30 to 89 mL per minute per 1.73 m(2) of body surface area, was found in 168 (44%) of the patients. Age, blood pressure, duration of hypertension, and plasma levels of fibrinogen, D-dimer, prothrombin fragment 1 + 2, and lipoprotein(a) were significantly greater in these patients than in those with normal renal function; these differences persisted after adjustment for potential confounders. Creatinine clearance was significantly and inversely correlated with levels of plasma fibrinogen (Spearman's rho = -0.26, P <0.001), D-dimer (rho = -0.33, P <0.001), and prothrombin fragment 1 + 2 (rho = -0.20, P <0.001). Levels of plasma fibrinogen (P = 0.009) and D-dimer (P = 0.003) were correlated with renal function independent of age, blood pressure, duration of hypertension, triglyceride level, urinary protein excretion, and erythrocyte sedimentation rate. Lipoprotein(a) levels were correlated with fibrinogen (rho = 0.16, P = 0.003) and D-dimer (rho = 0.26, P <0.001) levels.

CONCLUSIONS

Increased plasma levels of fibrinogen, D-dimer, and prothrombin fragment 1 + 2 are present in hypertensive patients with mildly decreased creatinine clearance, suggesting that the coagulation system is activated in these patients.

Characterization of insulin-resistance: role of receptor alteration in insulin-dependent diabetes mellitus, essential hypertension and cardiac hypertrophy

Insulin-resistance is associated with a number of disease states such as diabetes, syndrome X, and hypertension. These situations may be coupled to insulin-resistance through the insulin signaling system as a common pathway. The purpose of this study was to investigate the receptor binding alterations in streptozotocin-induced diabetic rats, spontaneously hypertensive rats and aortocaval shunted rats (eccentric cardiac hypertrophy). A physical model describing a 1:1 stoichiometry of ligand binding with its receptor is proposed describing reversible binding of [(125)I]insulin or [(125)I]IGF-1 at the microvascular endothelial as well as with the cardiac myocytes after CHAPS-treatment. Analysis of the collected effluents are curve-fitted with a conservation equation and a first-order Bessel function which allowed the calculation of the forward binding constants (k(n)), the reversible constants (k(-n)), the dissociation constants (k(d)) and the residency time constants (tau). The results showed that streptozotocin-induced diabetic rats showed insulin-resistance through alterations in the kinetics of insulin receptor binding. The normotensive controls of the spontaneously hypertension rats (SHR) carry themselves insulin-resistant receptors whose binding to insulin worsens in the hypertensive SHR. Negative cooperativity between insulin-like growth factor IGF-1 and insulin receptors could be a causative factor predisposing for insulin-resistance in the aortocaval shunted rats to insulin resistance. The defects may be occurring at the receptor level in insulin-dependent diabetes mellitus, Wistar-Kyoto rats and spontaneously hypertensive rats. In conclusion, alterations in the kinetics of insulin binding to its receptor seem to play a central role for the initiation of insulin-resistance during the various pathophysiological states.

The circulating hormonal milieu of the endocrine pancreas in healthy individuals, organ donors, and the isolated perfused human pancreas

Although basal circulating levels of individual islet cell hormones have been measured, few studies compared the molar ratios of the major hormones secreted by the endocrine pancreas. This study examined the basal levels of four major islet hormones: insulin, C-peptide (C-P), glucagon (G), and pancreatic polypeptide (PP) in normal subjects, in organ donors with brain death, and in the isolated perfused human pancreas. Basal blood samples were taken from normal, fasted control subjects (NCs). Pancreata were obtained from 17 organ donors (ODs) with donor portal vein (DPV) and radial arterial (DRA) blood samples taken before organ procurement. Single-pass perfusion was performed on the procured pancreata, and after rewarming and equilibration, basal samples were collected from the splenic vein (SV) for 30 min. Radioimmunoassays of insulin, C-P, G, and PP were performed on all samples, and basal levels of all hormones were expressed as a common unit, femtomoles per milliliter. The data suggest that in the basal state, these four major islet hormones circulate in a relatively constant molar ratio. The ratio of the hormones is altered in brain death and with in vitro perfusion of the pancreas. The isolated perfused human pancreas secretes a relatively constant molar ratio of these hormones; however, this ratio is markedly different from the circulating ratio seen in either the NC group or the OD group. We conclude that a relatively constant hormonal milieu is secreted from the normal endocrine pancreas, and this hormonal milieu is altered after brain death and with isolation and perfusion of the human pancreas.

Lipoprotein (a), haemostatic variables and cardiovascular damage in hypertensive patients

OBJECTIVE

Lipoproteins and coagulation factors are independent predictors of atherothrombotic events in the general population and their interaction may contribute to the development of cardiovascular damage. This study was designed to assess relationships between lipoproteins, haemostatic variables, and atherosclerotic complications in hypertensive patients.

METHODS

In 389 untreated essential hypertensive patients recruited at a hypertension clinic, we measured plasma lipids, apolipoproteins, lipoprotein (a), apolipoprotein (a) isoforms, fibrinogen, and parameters that directly reflect the coagulation activation. Hypertensive patients were compared to 92 normotensive controls.

RESULTS

Univariate analysis showed log lipoprotein (a) concentrations to be significantly correlated with age (P< 0.02), apolipoprotein B (P< 0.02), plasma fibrinogen (P< 0.001), and fibrin D-dimer (P< 0.001) levels, but not with body mass index, blood pressure, dietary fat intake, cholesterol, triglycerides, apolipoprotein Al, prothrombin fragment 1 + 2, and antithrombin III. The relationship of lipoprotein (a) with fibrinogen and D-dimer was present in both sexes, whereas the relationship of lipoprotein (a) with age and apolipoprotein B was found only in males. Multiple regression analysis showed that both fibrinogen and D-dimer were independently related with lipoprotein (a). Elevated fibrinogen, D-dimer, and lipoprotein (a) levels were significantly and independently associated with clinical evidence of atherosclerotic disease. To investigate whether the relationships of lipoprotein (a) with coagulation parameters are genetically determined, we analysed apolipoprotein (a) phenotypes in a subset of 188 hypertensive patients. While lipoprotein (a) levels were inversely correlated with apolipoprotein (a) isoform protein size, both fibrinogen and D-dimer concentrations were comparable in patients with apolipoprotein (a) isoforms of different size.

CONCLUSIONS

This study demonstrates a relationship between lipoprotein (a) and clotting variables in hypertensive patients that may contribute to atherosclerotic damage in these patients. There is no evidence of a genetic background for this relationship.

Lipoprotein(a) and apolipoprotein(a) isoforms and proteinuria in patients with moderate renal failure

BACKGROUND

Atherosclerotic diseases are a major cause of death in patients with renal failure. Increased serum concentrations of lipoprotein(a) [Lp(a)] have been established as a genetically controlled risk factor for these diseases and have been demonstrated in patients with moderate renal failure, suggesting that this lipoprotein contributes to the increased cardiovascular risk seen in these patients. Variable alleles at the apolipoprotein(a) [apo(a)] gene locus are the main determinants of the serum Lp(a) level in the general population. The purpose of this study was to investigate apo(a) isoforms in patients with moderate renal failure and mild proteinuria (less than 1.0 g/day).

METHODS

In 250 consecutive subjects recruited at a hypertension clinic, we assessed the renal function by 24-hour creatinine clearance, proteinuria, and microalbuminuria, as well as the prevalence of atherosclerotic disease, and we also measured apo(a) isoforms, serum albumin, and Lp(a) concentrations.

RESULTS

Moderate impairment of renal function (creatinine clearance, 30 to 89 ml/min per 1.73 m2 of body surface area) was found in 97 patients. Lp(a) levels were significantly greater in patients with moderate renal failure (21.7+/-23.9 mg/dl) as compared with patients with normal renal function (15.6+/-16.4 mg/dl, P<0.001), and an inverse correlation was observed between log Lp(a) and creatinine clearance (r = -0.181, P <0.01). However, no difference was found in the frequency of low molecular weight apo(a) isoforms between patients with normal (25.5%) and impaired (27.8%) renal function. Only patients with the smallest size apo(a) isoforms exhibited significantly elevated levels of Lp(a), whereas the large-size isoforms had similar concentrations in patients with normal and impaired renal function. No significant relationship was found between serum Lp(a) and proteinuria. Clinical and laboratory evidence of one or more events attributed to atherosclerosis was found in 9.8% of patients with normal renal function and 25.8% of patients with moderate renal failure (P<0.001).

CONCLUSIONS

These results indicate that renal failure per se or other genes beside the apo(a) gene locus are responsible for the elevation of serum Lp(a) levels in patients with moderate impairment of renal function. The elevation of Lp(a) levels occurs independently of the level of proteinuria and may contribute to the risk for atherosclerotic disease in these patients.

Mechanisms of insulin resistance in rat models of hypertension and their relationships with salt sensitivity

Several lines of evidence suggest that insulin resistance and the resultant hyperinsulinaemia are causally related to hypertension. Insulin actions are initiated by binding to a high-affinity transmembrane protein receptor which is present in all mammalian cells. These effects are predominant in skeletal muscle, liver, and fat and involve a number of tissue-specific and biochemically diverse events. Less well known are effects of insulin occurring in tissues not usually considered as insulin targets, which are hypothetical contributors to the pro-hypertensive action of the hormone. These effects include activation of renal sodium reabsorption, stimulation of the sympathetic nervous system, growth-promoting activity on vascular smooth muscle cells, and modulation of transmembrane cation transport. Epidemiological investigations have implicated sodium intake in the pathogenesis of hypertension. Because of the sodium-retaining effects of insulin, it has been postulated that insulin resistance with associated hyperinsulinaemia may be critical for the pathogenesis of salt-sensitivity in essential hypertensive subjects. Insulin resistance is present also in strains of rats with genetic hypertension that can be utilized as models to study the molecular mechanisms of this abnormality. In the present article, we summarize the current knowledge of the mechanisms of insulin resistance in rat models of arterial hypertension in which decreased sensitivity to insulin occurs and propose a rationale hypothesis that links insulin resistance with salt-sensitivity and hypertension.

Insulin-receptor binding characteristics in perfused SHR and WKY rat hearts

This work uses a new heart-perfusion technique to measure 125I-insulin binding on capillary endothelium and myofiber cell membranes in Wistar-Kyoto and spontaneously hypertensive rats. Ringer-Lock buffer was infused at a rate of 1 ml min-1 in the presence of 20 meq l-1 K+ and 125I-insulin through an aortic cannula. The effluent was collected through a catheter introduced into the right atrium. The capillary endothelial lining was removed by detergent treatment to expose the cardiac myocyte surfaces. A physical model describing a 1:1 binding stoichiometry of 125I-insulin with its receptors is proposed and the derived mathematical equations allow for the calculation of binding constants (kn), unbinding constants (k-n), dissociation constants (kd), and residency time constants (tau). The results showed that in the spontaneously hypertensive rats' hearts significant alterations were not noticed in the kinetics of insulin binding with its receptor at the capillary endothelial site compared to hearts of the normotensive control Wistar-Kyoto rats. However, at the myocyte site and in the spontaneously hypertensive rats, steric, configurational, and/or structural modifications for insulin binding with the receptor were observed as indicated by changes in insulin affinity for its receptor. Hence, alterations in insulin binding rather than reduction in insulin receptor number due to hyperinsulinemia, can be considered among the peculiarities of insulin resistance in the spontaneously hypertensive rats. Hyperinsulinemia, therefore, may be considered an upregulatory process as a consequence of insulin-resistance. The results support the hypothesis that insulin-resistance on the myocytes could be a pathophysiologic defect in insulin-receptor structure, function and affinity, and therefore myocardial function.

Relationship between insulin resistance and endothelium-dependent vascular relaxation in patients with essential hypertension

The infusion of L-arginine induces the production of nitric oxide and stimulates the immediate secretion of insulin. To examine the relationship between insulin resistance and endothelium-dependent vascular relaxation in patients with essential hypertension, we evaluated the renal and insulin responses to L-arginine, 500 mg/kg infused intravenously over 30 minutes, in 23 patients with mild essential hypertension who were neither obese nor diabetic and in 20 normotensive control subjects. We found no difference between the two groups in blood glucose or insulin in the fasting condition. The renovascular relaxation induced by L-arginine was significantly less in patients with essential hypertension than in normotensive control subjects. The increase in plasma cyclic GMP in response to L-arginine was lower in hypertensive patients than in normotensive subjects. Although the serum concentrations of glucose in response to L-arginine were similar in the two groups, the serum insulin response of the essential hypertensives was significantly higher than that of the normotensive subjects. In all subjects, the peak cyclic GMP response to L-arginine was significantly correlated with the peak delta glucose/ delta insulin ratio response to L-arginine (r = .69, P < .001). Findings suggested that an impairment of endothelium-dependent renal vascular relaxation and a reduced sensitivity to insulin are present in patients with essential hypertension. A link may be present between the abnormality of the L-arginine/nitric oxide/cyclic GMP pathway and insulin resistance in patients with essential hypertension.

Abnormalities of insulin receptors in spontaneously hypertensive rats

Insulin resistance is present in some strains of rats with genetic hypertension. To determine whether this abnormality is present at the level of the insulin receptor, we compared insulin sensitivity, insulin receptor binding, and mRNA levels in tissues of 10-week-old spontaneously hypertensive rats (SHR) and their normotensive Wistar-Kyoto (WKY) controls. Because we have previously demonstrated an inverse relationship between dietary sodium intake and renal insulin receptor density and mRNA levels in normal Sprague-Dawley rats, the two rat strains in the current experiment were fed either low salt (0.07% NaCl) or high salt (7.5% NaCl) chow until the SHR became hypertensive. Fasting plasma glucose and plasma insulin levels did not differ between SHR and WKY and were not affected by salt intake. When the rats were maintained on the low salt diet, the rate of glucose infusion required to main euglycemia during a hyperinsulinemic clamp was significantly lower in SHR than WKY. High salt diet decreased the rate of glucose utilization during the hyperinsulinemic clamp in WKY but not SHR. During the low salt diet, insulin infusion decreased sodium excretion in both WKY and SHR. When the rats were maintained on the high salt diet, the antinatriuretic response to insulin was blunted in WKY but not SHR. Both the density and mRNA levels of insulin receptor were comparable in the kidney of WKY and SHR, but only WKY had the previously demonstrated decrease in receptor number and mRNA levels when fed the high salt chow. Hepatic insulin receptor mRNA levels were significantly lower in SHR than WKY fed the low salt diet. High salt diet decreased significantly insulin receptor mRNA levels in the liver of WKY but not of SHR. Thus, SHR appear to have lost the feedback mechanism that normally limits insulin-induced sodium retention when extracellular volume is expanded. A decreased expression of insulin receptor in the liver of SHR provides a possible explanation for the insulin resistance and decreased insulin clearance present in this strain.