Hypertension, the potassium ion and impaired carbohydrate tolerance

Aldosterone and diabetic kidney disease

Aldosterone plays an important role in salt and water homeostasis and blood pressure control through the classical mineralocorticoid receptor. However, recent findings of the mineralocorticoid receptor in nonepithelial tissues suggest that aldosterone may have additional functions. Significant evidence now exists suggesting that aldosterone directly induces tissue injury. Systemic or local aldosterone has emerged as a multifunctional hormone exhibiting profibrotic and proinflammatory actions that extend beyond the classical hemodynamic effect. The incomplete blockade of the renin-angiotensin-aldosterone system by angiotensin-converting enzyme inhibitors or angiotensin II receptor blockers has led to experimental and clinical efforts using aldosterone inhibition. Recently, these efforts have provided us with an expanded understanding of a new pathogenic role for aldosterone in diabetic vascular complications. This article focuses on the role of aldosterone in the pathogenesis of diabetic kidney disease and recent important clinical data supporting the inhibition of aldosterone in treating diabetic kidney disease.

Hydrochlorothiazide and potassium chloride in comparison with hydrochlorothiazide and amiloride in the treatment of mild hypertension

A randomized, double-blind, cross-over study comparing 50 mg hydrochlorothiazide plus 5 mg amiloride (HCTZ/A) with 50 mg hydrochlorothiazide plus 26 mmol potassium chloride (HCTZ/K) was conducted in 18 patients with mild essential hypertension (diastolic pressure 90-105 mmHg). The sequence of treatment was: placebo for 2 weeks, one active drug for 3 weeks, placebo for 2 weeks, the other active drug for 3 weeks. The two agents were significantly and equally efficacious in lowering the systolic and diastolic blood pressure. Baseline vs. treatment mean serum potassium levels were 3.82 vs. 3.78 mmol/l for HCTZ/A and 3.82 vs. 3.70 mmol/l for HCTZ/K. The decrease in serum potassium level from baseline was significant for both agents but not significantly different when the two treatment forms were compared. Both treatment forms elevated fasting serum cholesterol and glucose. Serum triglycerides and uric acid rose significantly with HCTZ/K. Amiloride may affect the tubular handling of uric acid causing increased uric acid excretion, thus counteracting thiazide-induced hyperuricemia. During 3 weeks' extension of the main study, 5 patients received HCTZ/A in double the original dose (100 mg/10 mg) and 6 patients received HCTZ/K in double the original dose (100 mg/52 mmol). No further blood pressure reduction was observed on treatment with these doses. The mean serum potassium levels did not decrease further on doubling the HCTZ/A dose, while a significant fall was observed for HCTZ/K (3.60 vs. 3.42 mmol/l) (p less than 0.05, single tailed t-test). Both drug combinations were well tolerated and side-effects were not significantly different from those during placebo administration. This study demonstrates that 50 mg hydrochlorothiazide plus 26 mmol potassium chloride are as effective as 50 mg hydrochlorothiazide plus 5 mg amiloride, both in reducing blood pressure and preventing hypokalaemia in the treatment of essential hypertension. A small extension study indicates that amiloride might be more effective than potassium chloride in preventing hypokalaemia when high doses (100 mg/day) of hydrochlorothiazide are administered.

The effect of spironolactone on lipid, glucose and uric acid levels in blood during long-term administration to hypertensives

Spironolactone, an aldosterone antagonist, was given in a daily dose of 100 mg to 15 patients with primary hypertension for one year. Fasting levels of lipids, uric acid, glucose, insulin, potassium and growth hormone were measured before and after 6 and 12 months of treatment. Total cholesterol, LDL cholesterol, glucose, potassium and growth hormone were unchanged, HDL cholesterol fell from (mean +/- SD) 1.5 +/- 0.6 to 1.1 +/- 0.3 mmol/l (p less than 0.05) after 6 months of treatment and remained lowered (1.0 +/- 0.3 mmol/l) (p less than 0.01) after 12 months of treatment. There was a transient fall after 6 months of treatment in triglycerides from 2.4 +/- 1.5 to 2.0 +/- 1.1 mmol/l (p less than 0.05), uric acid from 380 +/- 73 to 342 +/- 58 mumol/l (p less than 0.05) and an increase in insulin from 16 +/- 9.5 to 28.6 +/- 26.8 mU/l (p less than 0.05). The blood glucose curves above fasting levels after glucose loading were unchanged during spironolactone treatment, whereas the area under the net insulin curve was higher after 6 months of treatment (163 +/- 103 mU X h/l) than before treatment (105 +/- 71 mU X h/l), indicating a small and transient insulin resistance. Thus, spironolactone impaired the glucose tolerance transiently and gave small and almost transient changes in fasting serum lipid and uric acid levels.

Fasting plasma glucose and serum lipids in patients with primary aldosteronism: a controlled cross-sectional study

An association between primary aldosteronism and metabolism disorders has been reported. The aim of this retrospective study was to test for this association by comparison between large cohorts of patients with primary aldosteronism and with essential hypertension. We retrieved the records of 460 cases with primary aldosteronism (103 lateralized, 150 not lateralized, and 207 undetermined) and of 1363 controls with essential hypertension individually matched for age and sex. We compared clinical history; blood pressure levels; body mass index; levels of fasting plasma glucose and serum triglycerides; total, high-density lipoprotein, and low-density lipoprotein cholesterol; and the prevalence of diabetes mellitus and impaired fasting glucose among subtypes of primary aldosteronism, as well as between cases with primary aldosteronism and their matched controls. Fasting plasma glucose and serum lipid levels did not differ among the 3 subtypes of primary aldosteronism. The prevalence of impaired fasting glucose was lower in patients with primary aldosteronism than their matched controls, but the prevalence of hyperglycemia (impaired fasting glucose or diabetes mellitus) and blood levels of glucose and lipids did not differ between cases and controls. There was no significant difference between preoperative and postoperative levels of either fasting plasma glucose or serum lipids in patients who underwent adrenalectomy and had follow-up data available. The analysis of this large group of patients with primary aldosteronism and essential hypertension does not confirm a higher prevalence of carbohydrate or lipid metabolism disorders in the former. It is unlikely that the prevalence of metabolic syndrome differs significantly between patients with primary aldosteronism and those with essential hypertension.

Inappropriate Left Ventricular Mass in Patients With Primary Aldosteronism

Assessment of appropriateness of left ventricular mass (LVM) for a given workload may better stratify hypertensive patients. Inappropriate LVM may reflect the interaction of genetic and neurohumoral factors other than blood pressure playing a significant role in myocardial growth. Primary aldosteronism (PA) represents a clinical model useful in assessing the effect of aldosterone increase on LVM. The aim of this study was to evaluate the inappropriateness of LVM in patients with PA. In 125 patients with PA (54 females; adrenal hyperplasia in 73 and adenoma in 52 patients) and in 125 age-, sex-, and blood pressure–matched, essential hypertensive patients, echocardiography was performed. The appropriateness of LVM was calculated by the ratio of observed LVM to the predicted value using a reference equation. In all of the subjects plasma renin activity and aldosterone, as well as clinic and 24-hour blood pressure, were measured. The prevalence of inappropriate LVM was greater in patients with traditionally defined left ventricular hypertrophy (70% and 44%, respectively; P =0.02) but also in patients without left ventricular hypertrophy (17% and 9%, respectively; P =0.085). In PA patients, a correlation was observed between the ratio of observed:predicted LVM and the ratio of aldosterone:plasma renin activity levels ( r =0.29; P =0.003) or the postinfusion aldosterone concentration ( r =0.44; P =0.004; n=42). In conclusion, in patients with PA, the prevalence of inappropriate LVM is increased, even in the absence of traditionally defined left ventricular hypertrophy. The increase in aldosterone levels could contribute to the increase of LV mass exceeding the amount needed to compensate hemodynamic load.

Renin-angiotensin system, natriuretic peptides, obesity, metabolic syndrome, and hypertension: an integrated view in humans

The obesity pandemic is closely related to hypertension and metabolic syndrome. Visceral adipose tissue plays a key role in the metabolic and cardiovascular complications of being overweight. The pathophysiological link between visceral adiposity and cardiometabolic complications focuses on insulin sensitivity, sympathetic nervous system, renin-angiotensin-aldosterone system (RAAS) and, only recently, on cardiac natriuretic peptide system (CNPS). RAAS and CNPS are endogenous antagonistic systems on sodium balance, cardiovascular system, and metabolism. The circulating RAAS is dysregulated in obese patients, and adipose tissue has a full local renin-angiotensin system that is active at local and systemic level. Adipocyte biology and metabolism are influenced by local renin-angiotensin system, with angiotensin II acting as a 'growth factor' for adipocytes. CNPS induces natriuresis and diuresis, reduces blood pressure, and, moreover, has powerful lipolytic and lipomobilizing activity in humans but not in rodents. In obesity, lower plasmatic natriuretic peptides levels with increasing BMI, waist circumference, and metabolic syndrome have been documented. Thus, reduced CNPS effects coupled with increased RAAS activity have a central role in obesity and its deadly complications. We propose herein an integrated view of the dysregulation of these two antagonistic systems in human obesity complicated with hypertension, metabolic syndrome, and increased cardiovascular risk.

The role of aldosterone in cardiovascular disease in people with diabetes and hypertension: an update

The role of mineralocorticoids in the development of cardiovascular disease (CVD), cardiometabolic syndrome, type 2 diabetes mellitus, chronic kidney disease (CKD), and hypertension is a growing field of interest. Aldosterone, mainly through nongenomic actions that result in proliferation, fibrosis, inflammation, and tissue remodeling, has been linked to CVD and CKD. Increased circulating aldosterone is also associated with insulin resistance and impaired glucose homeostasis that contribute to the development of endothelial dysfunction, atherosclerosis, and kidney disease. Aldosterone-induced oxidative stress and inflammation play a key role in impairing insulin signaling. Mineralocorticoid receptor blockade restores insulin sensitivity, counterbalances the deleterious cardiovascular and renal effects of aldosterone, and emerges as an alternative to improve blockade of the renin-angiotensin-aldosterone system, which potentially could contribute to reduce the burden of CVD and CKD.

The effect of body mass index on fasting blood glucose after initiation of thiazide therapy in hypertensive patients

BACKGROUND

The prevalence of obesity, hypertension, and type 2 diabetes mellitus is increasing in the United States. In this setting, it is important to understand the effects of antihypertensives on glucose metabolism. We therefore examined the association between body mass index (BMI) (kg/m(2)) and fasting blood glucose (FBG) in subjects in whom thiazide antihypertensive therapy had been initiated.

METHODS

A retrospective observational study was carried out on individuals with hypertension who had been started on thiazide therapy. The subjects' age, thiazide dose, BMI, serum potassium, FBG, new onset of diabetes mellitus, and concurrent use of other antihypertensives were included in the analysis. Predictors of change in FBG were analyzed using multiple linear regression analysis, while predictors of new-onset diabetes mellitus were determined using multiple logistic regression.

RESULTS

A total of 2,624 individuals who had been started on thiazide therapy for hypertension were divided into quartiles of increasing BMI. FBG was found to be associated with baseline BMI and, after thiazide initiation, there was a step-wise increase in the magnitude of change in FBG with increasing BMI (P < 0.001 for both). Analysis using multiple linear regression found that BMI and baseline FBG predicted the magnitude of FBG change in subjects initiated on thiazide treatment (P < 0.001 for both). Analysis with logistic regression found that, after thiazide initiation, BMI, serum potassium baseline (P < 0.05 for both), and baseline FBG (P < 0.001) predicted the development of diabetes mellitus.

CONCLUSIONS

There is an overall increase in FBG in individuals who are started on treatment with thiazides for hypertension. The magnitude of change in FBG and the development of new-onset diabetes mellitus after thiazide initiation were associated with increases in BMI and baseline FBG. American Journal of Hypertension (2008) doi:10.1038/ajh.2007.75American Journal of Hypertension (2008); 21 4. 438-442 doi:10.1038/ajh.2007.75.

The metabolic syndrome in primary aldosteronism

Patients with hypertension have a high prevalence of concurrent metabolic abnormalities (eg, obesity, dyslipidemia, and hyperglycemia). Clustering of these risk factors, defined as the metabolic syndrome, is associated with a high cardiovascular risk profile. This review summarizes current knowledge about the prevalence and characteristics of the metabolic syndrome in primary aldosteronism, and discusses the possible pathophysiological link between aldosterone and individual components of the metabolic syndrome, other than hypertension. Impaired glucose metabolism due to insulin resistance appears to be the major contributor to metabolic dysfunction in primary aldosteronism. Experimental observations support the possibility that aldosterone could act directly on insulin receptor function. The potential proadipogenic role of aldosterone and its negative effect on insulin sensitivity through production of cytokines remains to be investigated. Higher rates of cardiovascular events reported in primary aldosteronism could be due in part to the increased prevalence of the metabolic syndrome in this disorder.

A possible association between primary aldosteronism and a lower β-cell function

OBJECTIVE

Primary aldosteronism (PA) is the most common secondary cause of hypertension and recently has been implicated as a cause of impaired glucose tolerance. We investigated the glucose insulin sensitivity and insulin secretion in patients with idiopathic primary aldosteronism.

DESIGN

Thirty PA patients and 60 essential hypertensive (EH) patients as controls were included, matched (1: 2) by their body mass index (BMI) (29.9 +/- 4.3 versus 29.8 +/- 5.8 m/kg), age (53.7 +/- 9.4 versus 59.9 +/- 8.6 years old) and gender (male/female: 8/22 versus 17/43). In all patients, we measured insulin, total cholesterol, triglycerides, C-peptide and fasting glucose levels. Homeostasis model assessment for insulin resistance (HOMA-IR) and HOMA of pancreatic beta-cell function (HOMA-betaF) indexes were calculated. We also evaluated the response to spironolactone in 19 PA patients.

RESULTS

PA patients had higher levels of glucose (5.2 +/- 0.7 versus 4.9 +/- 0.7 mmol/l; P = 0.017). Insulin levels (10.7 +/- 6.5 versus 11.5 +/- 5.8 uUI/ml, P = 0.525) and HOMA-IR (2.51 +/- 1.59 versus 2.45 +/- 1.29 uUI/ml x mmol/l, P = 0.854) were similar in both groups. HOMA-betaF index (138.9 +/- 89.8 versus 179.8 +/- 100.2%, P = 0.049) and C-peptide (0.83 +/- 0.63 versus 1.56 +/- 0.84 ng/dl, P = 0.0001) were lower in PA patients. Potassium was normal in both groups. Negative correlations between serum aldosterone/plasma renin activity (SA/PRA) ratio and HOMA-betaF, and between C-peptide and SA levels were found in all patients. After the spironolactone treatment, we found an increase of C-peptide and insulin levels without changes in HOMA-IR or HOMA-betaF.

CONCLUSION

Our results showed differences in glucose metabolism between PA patients and those with hypertension suggesting that these findings could probably be determined by a lower beta-cell function influenced by aldosterone. These findings highlight the importance of aldosterone in glucose metabolism.

Aldosterone Suppresses Insulin Signaling Via the Downregulation of Insulin Receptor Substrate-1 in Vascular Smooth Muscle Cells

Clinical reports indicate that patients with primary aldosteronism commonly have impaired glucose tolerance; however, the relationship between aldosterone and insulin signaling pathway has not been clarified. In this study, we examined the effects of aldosterone treatment on insulin receptor substrate-1 expression and insulin signaling pathway including Akt phosphorylation and glucose uptake in rat vascular smooth muscle cells. Insulin receptor substrate-1 protein expression and Akt phosphorylation were determined by Western blot analysis with anti-insulin receptor substrate-1 and phosphorylated-Akt antibodies, respectively. Glucose metabolism was evaluated using (3)H-labeled 2-deoxy-d-glucose uptake. Aldosterone (1-100 nmol/L) dose-dependently decreased insulin receptor substrate-1 protein expression with a peak at 18 hours (n=4). Aldosterone-induced degradation of insulin receptor substrate-1 was markedly attenuated by treatment with the selective mineralocorticoid receptor antagonist eplerenone (10 micromol/L; n=4). Furthermore, degradation was blocked by the Src inhibitor PP1 (20 micromol/L; n=4). Treatment with antioxidants, N-acetylcysteine (10 mmol/L), or ebselen (40 micromol/L) also attenuated aldosterone-induced insulin receptor substrate-1 degradation (n=4). In addition, proteasome inhibitor MG132 (1 micromol/L) prevented insulin receptor substrate-1 degradation (n=4). Aldosterone treatment abolished insulin-induced Akt phosphorylation (100 nmol/L; 5 minutes; n=4). Furthermore, aldosterone pretreatment decreased insulin-stimulated (100 nmol/L; 60 minutes; n=4) glucose uptake by 50%, which was reversed by eplerenone (10 micromol/L; n=4). These data indicate that aldosterone decreases insulin receptor substrate-1 expression via Src and reactive oxygen species stimulation by proteasome-dependent degradation in vascular smooth muscle cells; thus, aldosterone may be involved in the pathogenesis of vascular insulin resistance via oxidative stress.

Aldosterone and end-organ damage

Aldosterone concentrations are inappropriately high in many patients with hypertension, as well as in an increasing number of individuals with metabolic syndrome and sleep apnoea. A growing body of evidence suggests that aldosterone and/or activation of the MR (mineralocorticoid receptor) contributes to cardiovascular remodelling and renal injury in these conditions. In addition to causing sodium retention and increased blood pressure, MR activation induces oxidative stress, endothelial dysfunction, inflammation and subsequent fibrosis. The MR may be activated by aldosterone and cortisol or via transactivation by the AT(1) (angiotenin II type 1) receptor through a mechanism involving the EGFR (epidermal growth factor receptor) and MAPK (mitogen-activated protein kinase) pathway. In addition, aldosterone can generate rapid non-genomic effects in the heart and vasculature. MR antagonism reduces mortality in patients with CHF (congestive heart failure) and following myocardial infarction. MR antagonism improves endothelial function in patients with CHF, reduces circulating biomarkers of cardiac fibrosis in CHF or following myocardial infarction, reduces blood pressure in resistant hypertension and decreases albuminuria in hypertensive and diabetic patients. In contrast, whereas adrenalectomy improves glucose homoeostasis in hyperaldosteronism, MR antagonism may worsen glucose homoeostasis and impairs endothelial function in diabetes, suggesting a possible detrimental effect of aldosterone via non-genomic pathways.

The metabolic syndrome in primary aldosteronism

Patients with hypertension have a high prevalence of concurrent metabolic abnormalities (eg, obesity, dyslipidemia, and hyperglycemia). Clustering of these risk factors, defined as the metabolic syndrome, is associated with a high cardiovascular risk profile. This review summarizes current knowledge about the prevalence and characteristics of the metabolic syndrome in primary aldosteronism, and discusses the possible pathophysiological link between aldosterone and individual components of the metabolic syndrome, other than hypertension. Impaired glucose metabolism due to insulin resistance appears to be the major contributor to metabolic dysfunction in primary aldosteronism. Experimental observations support the possibility that aldosterone could act directly on insulin receptor function. The potential proadipogenic role of aldosterone and its negative effect on insulin sensitivity through production of cytokines remains to be investigated. Higher rates of cardiovascular events reported in primary aldosteronism could be due in part to the increased prevalence of the metabolic syndrome in this disorder.

Addison's disease and the regulation of potassium: the role of insulin and aldosterone

It is proposed that insulin has a cardinal role in the regulation of serum potassium levels in man, which may be of greater importance than the effect of insulin on glucose metabolism. Although the first described action of insulin was on glucose transport, it is a hormone with many functions some of which may operate in a metabolic hierarchy depending on the relative importance of the action required. Insulin also promotes the transport of potassium ions from the extracellular space to the intracellular space and it is suggested that there are occasions where this action may take place at the expense of glucose regulation. In metabolic terms, tight control of serum potassium is of greater importance than precise control of serum glucose, because quite small variations in serum potassium may cause death whereas wide variations in serum glucose may be tolerated. Serum potassium levels generally remain very stable despite large daily variations in potassium intake. It follows that potassium control mechanisms must be of outstanding efficiency as serious disturbances of potassium balance are relatively uncommon. 'Nature makes experiments on Man': shadowy but important physiological mechanisms that may almost be taken for granted in normal health are often brightly illuminated by unusual pathological conditions. This paper describes two remarkable patients who presented with extreme hyperkalaemia. This condition was the result of simultaneous insulin and aldosterone deficiency occurring because of concomitant diabetes and Addison's disease. Other medical conditions with disturbances in aldosterone, insulin and potassium control will be referred to in support of the hypothesis that insulin secretion is central to potassium regulation. This hypothesis explains the secondary disturbances in glucose metabolism that occurs in clinical situations where the primary problem is perturbation of potassium regulation.

The Prevalence of Primary Aldosteronism in Diabetic Patients

Increased plasma aldosterone concentrations (PACs) are associated with higher cardiovascular risk and target organ damage (TOD). Hyperglycemia can potentiate the cellular effects of aldosterone, and the prevalence of diabetes in primary aldosteronism (PA) is 7%-59%. The prevalence of PA in hypertensive individuals is estimated to be 10%-14%. This study of 61 hypertensive diabetic patients not taking spironolactone and with serum creatinine values <2.5 mg/dL sought to establish the prevalence of PA in hypertensive diabetics and compare the prevalence of PA in patients with TOD with those patients without TOD. PA was suspected if PACs were >15 ng/dL and plasma renin activity was <1 ng/dL/h (ratio >30). Although 14 patients had suppressed renin with PACs >8 ng/dL (including two with PACs >11 ng/dL), none met our criteria for PA. There was no correlation between PAC and TOD. This study indicates that routine screening for PA in hypertensive diabetic patients is not justified and that PAC does not correlate with TOD. Further study is needed.

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.

Effects of valsartan compared to amlodipine on preventing type 2 diabetes in high-risk hypertensive patients: the VALUE trial

CONTEXT

Type 2 diabetes is emerging as a major health problem, which tends to cluster with hypertension in individuals at high risk of cardiovascular disease.

OBJECTIVE

To test for the first time the hypothesis that treatment of hypertensive patients at high cardiovascular risk with the angiotensin-receptor blocker (ARB) valsartan prevents new-onset type 2 diabetes compared with the metabolically neutral calcium-channel antagonist (CCA) amlodipine.

DESIGN

Pre-specified analysis in the VALUE trial. Follow-up averaged 4.2 years. The risk of developing new diabetes was calculated as an odds ratio (OR) with 95% confidence intervals (CI) for different definitions of diabetes.

PATIENTS

A sample of 9995 high-risk, non-diabetic hypertensive patients.

INTERVENTIONS

Valsartan or amlodipine with or without add-on medication [hydrochlorothiazide (HCTZ) and other add-ons, excluding other ARBs, angiotensin-converting enzyme (ACE) inhibitors, CCAs].

MAIN OUTCOME MEASURE

New diabetes defined as an adverse event, new blood-glucose-lowering drugs and/or fasting glucose > 7.0 mmol/l.

RESULTS

New diabetes was reported in 580 (11.5%) patients on valsartan and in 718 (14.5%) patients on amlodipine (OR 0.77, 95% CI 0.69-0.87, P < 0.0001). Using stricter criteria (without adverse event reports) new diabetes was detected in 495 (9.8%) patients on valsartan and in 586 (11.8%) on amlodipine (OR 0.82, 95% CI 0.72-0.93, P = 0.0015).

CONCLUSION

Compared with amlodipine, valsartan reduces the risk of developing diabetes mellitus in high-risk hypertensive patients.

Antihypertensive treatment and new-onset diabetes mellitus

The various antihypertensive regimens have varying effects on glucose metabolism and the development of diabetes mellitus. Recent large hypertension trials have shown great differences in the development of new-onset diabetes among antihypertensive drug therapies. The incidence of diabetes is unchanged or increased by thiazide diuretics and b-adrenergic blockers, and unchanged or decreased by angiotensin-converting enzyme inhibitors, calcium channel blockers, and angiotensin-receptor blockers. The differences in new-onset diabetes mellitus have not influenced the outcome of cardiovascular mortality and morbidity in all of the large clinical trials, but drug-induced diabetes among hypertensive patients is known to carry the same cardiovascular risk as that seen in patients with previously known diabetes; however, it might take years for the increased risk to become apparent.

Therapeutic Controversies in Hypertension

Although numerous prospective randomized trials since the Veterans Administration studies clearly have attested to the efficacy and safety of antihypertensive therapy, there remain some controversial issues with all classes of antihypertensive drugs. Thiazide diuretics increase the risk for new-onset diabetes and their long-term safety has been questioned. Alpha-blockers do not reduce morbidity and mortality in uncomplicated hypertension but are well known to cause a variety of poorly tolerated side effects. The safety of calcium antagonists has been questioned for many years, although recent large prospective randomized trials such as Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial, International Verapamil-Trandolapril Study, Intervention as a Goal in Hypertension, Valsartan Antihypertensive Long-Term Use Evaluation and the Anglo-Scandinavian Cardiac Outcomes Trial (ASCOT) have attested to their safety and efficacy. Angiotensin-converting enzyme inhibitors, in general, are well tolerated but have potentially fatal adverse effects in a few patients. Angiotensin-receptor blockers are exceedingly well tolerated, but may be less-efficacious antihypertensive agents than other drug classes. Most antihypertensive drug classes have an effect on new-onset diabetes that should be taken into account in patients at risk. No head-to-head comparison of combination therapy looking at efficacy and safety has been available. The long-term safety of antihypertensive therapy is documented poorly because most trials only last 4 to 6 years. Despite these drawbacks and concerns, the benefits of antihypertensive therapy clearly outweigh its potential risk.

The renin-angiotensin-aldosterone system, glucose metabolism and diabetes

In diabetes mellitus (DM), the circulating renin-angiotensin system (RAS) is suppressed, but the renal tissue RAS is activated. Hyperglycemia increases tissue angiotensin II (Ang II), which induces oxidative stress, endothelial damage and disease pathology including vasoconstriction, thrombosis, inflammation and vascular remodeling. In early DM, the type 1 Ang II (AT(1)) receptor is upregulated but the type 2 Ang II (AT(2)) receptor is downregulated. This imbalance can predispose the individual to tissue damage. Hyperglycemia also increases the production of aldosterone, which has an unknown contribution to tissue damage. The insulin resistance state is associated with upregulation of the AT(1) receptor and an increase in oxygen free radicals in endothelial tissue caused by activation of NAD(P)H oxidase. Treatment with an AT(1) receptor blocker normalizes oxidase activity and improves endothelial function. An understanding of the tissue renin-angiotensin-aldosterone system, which is a crucial factor in the progression of tissue damage in DM, is imperative for protection against tissue damage in this chronic disease.

Prevention of type 2 diabetes mellitus through inhibition of the Renin-Angiotensin system

Type 2 diabetes mellitus is becoming a major health problem associated with excess morbidity and mortality. As the prevalence of type 2 diabetes is rapidly increasing, prevention of the disease should be considered as a key objective in the near future. Besides lifestyle changes, various pharmacological treatments have proven their efficacy in placebo-controlled clinical trials, including antidiabetic drugs such as metformin, acarbose and troglitazone, or antiobesity agents such as orlistat. Arterial hypertension, a clinical entity in which insulin resistance is common, is strongly associated with type 2 diabetes and may precede the disease by several years. While antihypertensive agents such as diuretics or beta-adrenoceptor antagonists may worsen insulin resistance and impair glucose tolerance, newer antihypertensive agents exert neutral or even slightly positive metabolic effects. Numerous clinical trials have investigated the effects of ACE inhibitors or angiotensin II receptor antagonists (ARAs) on insulin sensitivity in hypertensive patients, with or without diabetes, with no consistent results. Almost half of the studies with ACE inhibitors in hypertensive nondiabetic individuals demonstrated a slight but significant increase in insulin sensitivity as assessed by insulin-stimulated glucose disposal during a euglycaemic hyperinsulinaemic clamp, while the other half failed to reveal any significant change. The effects of ARAs on insulin sensitivity are neutral in most studies. Mechanisms of improvement of glucose tolerance and insulin sensitivity through the inhibition of the renin-angiotensin system (RAS) are complex. They may include improvement of blood flow and microcirculation in skeletal muscles and, thereby, enhancement of insulin and glucose delivery to the insulin-sensitive tissues, facilitating insulin signalling at the cellular level and improvement of insulin secretion by the beta cells. Six recent large-scale clinical studies reported a remarkably consistent reduction in the incidence of type 2 diabetes in hypertensive patients treated with either ACE inhibitors or ARAs for 3-6 years, compared with a thiazide diuretic, beta-adrenoceptor antagonist, the calcium channel antagonist amlodipine or even placebo. The relative risk reduction averaged 14% (p = 0.034) in the CAPPP (Captopril Prevention Project) with captopril compared with a thiazide or beta1-adrenoceptor antagonist, 34% (p < 0.001) in the HOPE (Heart Outcomes Prevention Evaluation) study with ramipril compared with placebo, 30% (p < 0.001) in the ALLHAT (Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial) with lisinopril compared with chlortalidone, 25% (p < 0.001) in the LIFE (Losartan Intervention For Endpoint reduction in hypertension study) with losartan compared with atenolol, and 25% (p = 0.09) in the SCOPE (Study on Cognition and Prognosis in the Elderly) with candesartan cilexetil compared with placebo, and 23% (p < 0.0001) in the VALUE (Valsartan Antihypertensive Long-term Use Evaluation) trial with valsartan compared with amlodipine. All these studies considered the development of diabetes as a secondary endpoint, except the HOPE trial where it was a post hoc analysis. These encouraging observations led to the initiation of two large, prospective, placebo-controlled randomised clinical trials whose primary outcome is the prevention of type 2 diabetes: the DREAM (Diabetes REduction Approaches with ramipril and rosiglitazone Medications) trial with the ACE inhibitor ramipril and the NAVIGATOR (Nateglinide And Valsartan in Impaired Glucose Tolerance Outcomes Research) trial with the ARA valsartan. Finally, ONTARGET (ONgoing Telmisartan Alone and in combination with Ramipril Global Endpoint Trial) will also investigate as a secondary endpoint whether it is possible to prevent the development of type 2 diabetes by blocking the RAS with either an ACE inhibitor or an ARA or a combination of both. Thus, the recent consistent observations of a 14-34% reduction of the development of diabetes in hypertensive patients receiving ACE inhibitors or ARAs are exciting. From a theoretical point of view, they emphasise that there are many aspects of the pathogenesis, prevention and treatment of type 2 diabetes that still need to be uncovered. From a practical point of view, they may offer a new strategy to reduce the ongoing epidemic and burden of type 2 diabetes.

Evolution of diagnostic criteria for primary aldosteronism: why is it more common in "drug-resistant" hypertension today?

The recent "epidemic" of primary aldosteronism reported in the literature is most likely related to the widespread acceptance that with easy access to accurate measurements of renin and aldosterone, it is no longer necessary to wait until hypokalemia has become profound before embarking on diagnostic testing to attempt to ferret out this most common cause of "essential" hypertension. This is especially true for those who are now classified as "drug resistant" using today's popular drugs, which are particularly ineffective in lowering blood pressure in primary aldosteronism and its variants. Understanding the physiologic consequences of a slowly increasing aldosterone production by autonomous cells will help both the family practitioner and the specialist understand the role of the aldosterone renin ratio (ARR) in the care of the hypertensive patient. In addition, the increasing number of specific genetic mutations that drive sodium retention and lead to low levels of renin activity and familial hypertension must be incorporated into the routine evaluation and care of hypertensive patients and their families.

Renin-angiotensin system inhibition prevents type 2 diabetes mellitus

The inhibition of the renin-angiotensin system (RAS) with either angiotensin converting enzyme inhibitors (ACEIs) or AT1 angiotensin receptor blockers (ARBs) consistently and significantly reduces the incidence of type 2 diabetes in patients with hypertension or congestive heart failure. The mechanisms underlying this protective effect appear to be complex and may involve an improvement of both insulin sensitivity and insulin secretion. These two effects may result, at least in part, from the well known effects of these pharmacological agents on the vascular system on the one hand, on the ionic balance on the other hand. Indeed, the vasodilation induced by ACEIs or ARBs could improve the blood circulation in skeletal muscles, thus favouring peripheral insulin action, but also in the pancreas, thus promoting insulin secretion. Preserving cellular potassium and magnesium pools by blocking the aldosterone effects could also improve both cellular insulin action and insulin secretion. However, besides these classical effects, new mechanisms have been recently suggested. A direct effect of the inhibition of angiotensin and/or of the enhancement of bradykinin on various steps of the insulin cascade signalling has been described as well an increase in GLUT4 glucose transporters after RAS inhibition. Furthermore, it has been demonstrated that angiotensin II inhibits adipogenic differentiation of human adipocytes via A1 receptors and, therefore, it has been hypothesised that RAS blockade may prevent diabetes by promoting the recruitment and differentiation of adipocytes. Finally, some lipophilic ARBs appear to induce PPAR-gamma activity in the adipose tissue. Hence, the protection against type 2 diabetes observed after RAS inhibition may be partially linked to a thiazolidinedione-like effect. In conclusion, numerous physiological and biochemical mechanisms could explain the protective effect of RAS inhibition against the development of type 2 diabetes in individuals with arterial hypertension or congestive heart failure. What might be the main mechanism in the overall protection effect of ACEIs or ARBs remains an open question.

Old antihypertensives and new diabetes

Diuretic antihypertensive therapy is recommended as first choice by many guidelines, often in combination with beta-blockers. However, such recommendations are based on relatively short-term trials, whereas treatment for hypertension is often a lifetime process. A meta-analysis of seven studies in 58,010 individuals, showed that the 'new' therapies, namely angiotensin-converting enzyme (ACE) inhibitors, angiotensin II type 1 receptor blockers (ARBs) and calcium channel blockers (CCBs) provoke less new diabetes than the conventional 'old' therapies (diuretics and beta-blockers). ACE inhibitors/ARBs decreased new diabetes by 20% (P < 0.001), whereas CCBs decreased new diabetes by 16% (P < 0.001). The number needed to treat for approximately 4 years by new rather than old conventional therapy to avoid one case of new diabetes is about 60-70. Other factors contributing to increased coronary risk are increased metabolic syndrome, blood lipid changes and hypokalaemia. It is not certain whether it is the new therapy that provides protection against new diabetes or the conventional therapy that precipitates new diabetes. However, when compared with placebo, ACE inhibition by ramipril or by the ARB, candesartan, both decrease the incidence of new diabetes, raising the hypothesis that these agents actually prevent the changes leading to insulin resistance, possibly by lessening the adverse effects of angiotensin II on the endothelium. Conversely, lipid abnormalities with conventional treatment could exert adverse effects on the endothelium. Therefore endothelial changes could help to explain the benefits of 'modern' treatment compared with the defects of conventional therapy.

Aldosterone stimulates gene expression of hepatic gluconeogenic enzymes through the glucocorticoid receptor in a manner independent of the protein kinase B cascade

Primary aldosteronism is associated with glucose intolerance and diabetes, which is due in part to impaired insulin release caused by reduction of potassium, although other possibilities remain to be elucidated. To evaluate the in vivo effects of aldosterone on glucose metabolism, a single dose of aldosterone was administered to mice, which resulted in elevation of the blood glucose level. In primary cultured mouse hepatocytes, the gene expression of gluconeogenic enzymes such as glucose-6-phosphatase (G6Pase), fructose-1,6-bisphosphatase and phosphoenolpyruvate carboxykinase increased in response to aldosterone in a dose-dependent manner even at a concentration similar to a physiological condition (10(-9) M). The inhibitory effect of insulin on G6Pase gene expression was partially suppressed by aldosterone. Furthermore, aldosterone enhanced G6Pase promoter activity in human hepatoma cell line HepG2, which was prevented by co-treatment with a glucocorticoid antagonist RU-486, but not a mineralocorticoid antagonist spironolactone. In contrast, aldosterone had no effects on major insulin signaling pathways including insulin receptor substrate-1, protein kinase B, and forkhead transcription factor. These results suggest that aldosterone may affect the inhibitory effect of insulin on hepatic gluconeogenesis through the glucocorticoid receptor, which may be one of the causes of impaired glucose metabolism in primary aldosteronism.

The effect of aldosterone on glucose metabolism

There is an association of glucose intolerance and diabetes with primary aldosteronism, but the frequency and mechanisms are not clear. This paper reviews the possible mechanisms of impaired glucose metabolism in primary aldosteronism. Patients with primary aldosteronism can have impaired pancreatic insulin release and reduction in insulin sensitivity. These effects may be due to hypokalemia, but the evidence suggests other factors such as a direct impact of excess aldosterone on insulin action in contributing to the metabolic dysfunction. In general adrenal surgery in cases of aldosterone-producing adenoma will correct the metabolic abnormalities, but it is less sure if treatment with spironolactone in cases of idiopathic hyperplasia will correct impaired glucose tolerance.

Familial hyperaldosteronism

Aldosterone, the major circulating mineralocorticoid, participates in blood volume and serum potassium homeostasis. Primary aldosteronism is a disorder characterised by hypertension and hypokalaemia due to autonomous aldosterone secretion from the adrenocortical zona glomerulosa. Improved screening techniques, particularly application of the plasma aldosterone:plasma renin activity ratio, have led to a suggestion that primary aldosteronism may be more common than previously appreciated among adults with hypertension. Glucocorticoid-remediable aldosteronism (GRA) was the first described familial form of hyperaldosteronism. The disorder is characterised by aldosterone secretory function regulated chronically by ACTH. Hence, aldosterone hypersecretion can be suppressed, on a sustained basis, by exogenous glucocorticoids such as dexamethasone in physiologic range doses. This autosomal dominant disorder has been shown to be caused by a hybrid gene mutation formed by a crossover of genetic material between the ACTH-responsive regulatory portion of the 11ss-hydroxylase (CYP11B1) gene and the coding region of the aldosterone synthase (CYP11B2) gene. Familial hyperaldosteronism type II (FH-II), so named to distinguish the disorder from GRA or familial hyperaldosteronism type I (FH-I), is characterised by autosomal dominant inheritance of autonomous aldosterone hypersecretion which is not suppressible by dexamethasone. Linkage analysis in a single large kindred, and direct mutation screening, has shown that this disorder is unrelated to mutations in the genes for aldosterone synthase or the angiotensin II receptor. The precise genetic cause of FH-II remains to be elucidated.

Anaesthesia for Conn's syndrome

We describe the peri-operative management of two patients undergoing bilateral adrenalectomy for Conn's syndrome; one using an open surgical approach and the other a laparoscopic technique. The first patient, aged 64 years, died of a myocardial infarction 5 days postoperatively; the second, aged 29 years, had an uneventful recovery. The pre-operative preparation, peroperative management and postoperative care of these patients are detailed, and the pathophysiology and clinical management of Conn's syndrome are reviewed.

In vivo tissue specific modulation of rat insulin receptor gene expression in an experimental model of mineralocorticoid excess

Insulin receptor (IR) gene expression at the mRNA level was investigated in hindlimb skeletal muscle, epididymal adipose tissue and in the liver of rats exposed to prolonged in vivo administration of deoxycorticosterone acetate (DOCA). Following treatment, plasma insulin levels were reduced while glucose levels increased compared to values in control rats. DOCA-treated animals showed an increase in blood pressure and a reduction in body weight. This treatment also induced hypokalemia and decreased plasma protein levels. Sodium levels were unaffected. Moreover, no differences in DNA and protein content or in the indicator of cell size (protein/DNA) were observed in the skeletal muscle or adipose tissue of animals. In contrast, there was a clear increase in the protein and DNA contents of the liver with no change in the indicator of cell size. Northern blot assays revealed 2 major IR mRNA species of approximately 9.5 and 7.5 Kb in the 3 tissues from control animals. DOCA treatment induced no change in the levels of either RNA species in skeletal muscle. However, a decrease of approximately 22% was detected in the levels of both species in adipose tissue whereas the liver showed an increase of 64%. These results provide the first evidence for an in vivo tissue-specific modulation of IR mRNA levels under experimental conditions of mineralocorticoid excess.

Hyperglycemia, lumbar plexopathy and hypokalemic rhabdomyolysis complicating Conn's syndrome

BACKGROUND

Lumbosacral plexopathy is a complication of diabetes mellitus. Conn's syndrome from an aldosterone secreting adenoma may be associated with hypokalemia and rhabdomyolysis but mild hyperglycemia also usually occurs.

METHODS

Case description.

RESULTS

A 70-year-old male diagnosed as having Conn's syndrome, hypokalemia and mild hyperglycemia developed rhabdomyolysis and lumbar plexopathy as a presenting feature of his hyperaldosteronism. His rhabdomyolysis rapidly cleared following correction of hypokalemia but recovery from the plexopathy occurred slowly over several months. Definite resection of the aldosterone secreting adenomas reversed the hyperglycemia.

CONCLUSIONS

Our patient developed lumbar plexopathy resembling that associated with diabetes mellitus despite the presence of only mild and transient hyperglycemia.

Increased insulin sensitivity in patients with aldosterone producing adenoma

OBJECTIVE

Primary aldosteronism is a recognized endocrine cause of glucose intolerance. A blunted insulin response to glucose in patients with primary aldosteronism is well known, but insulin sensitivity has not been thoroughly determined. We investigated insulin sensitivity and insulin secretion in patients with aldosterone producing adenoma.

DESIGN

Glucose tolerance and insulin responses to glucose were evaluated using a standard 75 g oral glucose tolerance test in patients with aldosterone producing adenoma before and after surgery, and in control subjects. Parameters for insulin resistance (HOMA-R) and pancreatic beta-cell function (HOMA-beta F) were derived from a homeostasis model assessment.

PATIENTS

Fifteen patients with aldosterone producing adenoma and 41 control subjects with normal glucose tolerance matched for age and body mass index, were studied. Eight patients were re-evaluated after surgical removal of the adenoma. In 5 patients 125I-insulin binding to erythrocytes was also measured.

MEASUREMENTS

Plasma glucose was measured by a glucose oxidase method. Plasma insulin, aldosterone and renin activity were measured by radioimmunoassay.

RESULTS

Both fasting plasma glucose and insulin were lower in the patients than in the controls. Although the areas under the curve for plasma glucose during the oral glucose tolerance test did not differ, that for plasma insulin was less in the patients with hyperaldosteronism. Insulin sensitivity was increased in the patients, as evidenced by decreased HOMA-R compared with controls, while HOMA-beta F was comparable between the groups. 125I-insulin binding to erythrocytes was higher in 5 patients than in 19 normal controls. After surgical removal of adenoma, neither fasting plasma glucose nor the glucose area under the curve during the oral glucose tolerance test changed. However, fasting plasma insulin and the insulin area under the curve increased significantly. HOMA-R increased and HOMA-beta F remained unaltered.

CONCLUSION

Insulin sensitivity was increased in untreated patients with aldosterone producing adenoma. Enhanced insulin receptor binding may contribute to this increased insulin sensitivity.

Drug-induced diabetes

The only drugs which commonly cause diabetes during therapeutic use are the anti-hypertensive vasodilator diazoxide, and corticosteroids in high doses such as those used to palliate intracranial tumours. Thiazide diuretics have in the past been used in higher doses than necessary to treat hypertension, and the lower doses now used probably carry only a slight risk of inducing diabetes. The risk from beta-blockers is also quite small, but there is some evidence that thiazides combined with beta-blockers may be more likely to cause diabetes than either drug alone. The combination is probably best avoided in patients with a family history of non-insulin-dependent diabetes. The effect of the low-oestrogen combined oral contraceptive pill seems to be slight, and it presents a risk only to women who have had gestational diabetes. Bodybuilders who take enormous doses of anabolic-androgens can develop impaired glucose tolerance. Several drugs, including theophylline, aspirin, isoniazid and nalidixic acid can cause transient hyperglycaemia in overdosage, but only streptozotocin, alloxan and the rodenticide Vacor are likely to cause permanent diabetes.