In vitro effects of insulin on aldosterone production in rat zona glomerulosa cells

Effect of the interaction between the visceral-to-subcutaneous fat ratio and aldosterone on cardiac function in patients with primary aldosteronism

Primary aldosteronism is the most frequent secondary hypertensive disease and is characterized by an elevated risk for cardiovascular disease. The current standard treatments are adrenalectomy and/or administration of mineralocorticoid receptor blockers, both of which are effective at ameliorating hypertension via intervention for hyperaldosteronism. However, both of these approaches have side effects and contraindications, and mineralocorticoid receptor blockers also have limited preventive efficacy against cardiovascular events. Recently, in vitro experiments have shown that aldosterone regulation is closely related to abdominal fat accumulation and that there is crosstalk between aldosterone and visceral fat tissue accumulation. We previously reported that this interaction was clinically significant in renal dysfunction; however, its effects on the heart remain unclear. Here, we analyzed data from 49 patients with primary aldosteronism and 29 patients with essential hypertension to examine the potential effect of the interaction between the ratio of visceral-to-subcutaneous fat tissue volume and the plasma aldosterone concentration on echocardiographic indices, including the tissue Doppler-derived E/e' ratio. A significant interaction was found in patients with primary aldosteronism (p < 0.05), indicating that patients with the combination of a high plasma aldosterone concentration and high visceral-to-subcutaneous fat ratio show an increased E/e' ratio, which is a well-known risk factor for future cardiovascular events. Our results confirm the clinical importance of the interaction between aldosterone and abdominal fat tissue, suggesting that an improvement in the visceral-to-subcutaneous fat ratio may be synergistically and complementarily effective in reducing the elevated risk of cardiovascular disease in patients with primary aldosteronism when combined with conventional therapies for reducing aldosterone activity. A significant effect of the interaction between plasma aldosterone concentration and the visceral-to-subcutaneous fat ratio on the tissue Doppler-derived E/e' ratio in patients with primary aldosteronism.

Secondary diabetes mellitus due to primary aldosteronism

Primary aldosteronism (PA) and diabetes mellitus (DM) are clinical conditions that increase cardiovascular risk. Approximately one in five patients with PA have DM. Nevertheless, the pathophysiology linking these two entities is not entirely understood. In addition, the majority of patients with PA have glucocorticoid co-secretion, which is associated with increased risk of impaired glucose homeostasis. In the present review, we aim to comprehensively discuss all the available research data concerning the interplay between mineralocorticoid excess and glucose metabolism, with separate analysis of the sequalae in muscle, adipose tissue, liver and pancreas. Aldosterone binds both mineralocorticoid and glucocorticoid receptors and amplifies tissue glucocorticoid activity, via 11-β-hydroxysteroid dehydrogenase type 1 stimulation. A clear classification of the molecular events as per specific receptor in insulin-sensitive tissues is impossible, while their synergistic interaction is plausible. Furthermore, aldosterone induces oxidative stress and inflammation, perturbs adipokine expression, thermogenesis and lipogenesis in adipose tissue, and increases hepatic steatosis. In pancreas, enhanced oxidative stress and inflammation of beta cells, predominantly upon glucocorticoid receptor activation, impair insulin secretion. No causality between hypokalemia and impaired insulin response is yet proven; in contrast, hypokalemia appears to be implicated with insulin resistance and hepatic steatosis. The superior efficacy of adrenalectomy in ameliorating glucose metabolism vs. mineralocorticoid receptor antagonists in clinical studies highlights the contribution of non-mineralocorticoid receptor-mediated mechanisms in the pathophysiologic process. The exact role of hypokalemia, the mechanisms linking mineralocorticoid excess with hepatic steatosis, and possible disease-modifying role of pioglitazone warrant further studies.

Differences in Glycemic Abnormalities Between Primary Aldosteronism and Essential Hypertension: A Systematic Review and Meta-Analysis

Background

The relationship of glycemic abnormalities between primary aldosteronism (PA) patients and essential hypertension (EH) patients is still debatable. This meta-analysis aimed to explore differences in the prevalence of glycemic abnormalities and levels of abnormal glucose metabolism in PA and EH patients.

Methods

A search was performed using PubMed, Scopus, Cochrane and Web of Science databases from their inception through January 2022. Inclusion criteria for this study were 1) observational studies which contained specific data of interest, 2) studies including data which compared adult PA and EH patients and 3) studies which used appropriate methods to diagnose PA. Risk ratio (RR) or standardized mean difference (SMD) with a 95% confidence interval (95% CI) was calculated.

Results

Twenty-six studies involving 53,186 patients were included in the meta-analysis. Patients with PA demonstrated significantly higher overall incidence of glycemic abnormalities than patients with EH [RR 1.54; 95% CI (1.20,1.98)]. Risk of diabetes mellitus (DM) and impaired glucose tolerance (IGT) in PA patients were higher than in EH patients [RR 1.27; 95%CI (1.08, 1.49) and RR 2.99; 95%CI (1.74, 5.16), respectively]. There was no statistically significant difference of risk between these groups for impaired fasting glucose (IFG) [RR 1.70; 95%CI (0.55, 5.26)]. Moderate heterogeneity was observed in overall glycemic abnormalities outcomes. A high level of heterogeneity was observed for IFG, while the level was low for DM and IGT.

Conclusions

PA patients have a higher risk of glycemic abnormalities than in EH patients. Further study should be conducted to investigate underlying mechanisms of glycemic abnormalities in PA.

Systematic Review Registration

www.inplasy.com, INPLASY, identifier 202220004.

Metabolic syndrome in hypertensive patients: An unholy alliance

For many years, it has been recognized that hypertension tends to cluster with various anthropometric and metabolic abnormalities including abdominal obesity, elevated triglycerides, reduced high-density lipoprotein cholesterol, glucose intolerance, insulin resistance and hyperuricemia. This constellation of various conditions has been transformed from a pathophysiological concept to a clinical entity, which has been defined metabolic syndrome (MetS). The consequences of the MetS have been difficult to assess without commonly accepted criteria to diagnose it. For this reason, on 2009 the International Diabetes Federation, the American Heart Association and other scientific organizations proposed a unified MetS definition. The incidence of the MetS has been increasing worldwide in parallel with an increase in overweight and obesity. The epidemic proportion reached by the MetS represents a major public health challenge, because several lines of evidence showed that the MetS, even without type 2 diabetes, confers an increased risk of cardiovascular morbidity and mortality in different populations including also hypertensive patients. It is likely that the enhanced cardiovascular risk associated with MetS in patients with high blood pressure may be largely mediated through an increased prevalence of preclinical cardiovascular and renal changes, such as left ventricular hypertrophy, early carotid atherosclerosis, impaired aortic elasticity, hypertensive retinopathy and microalbuminuria. Indeed, many reports support this notion, showing that hypertensive patients with MetS exhibit, more often than those without it, these early signs of end organ damage, most of which are recognized as significant independent predictors of adverse cardiovascular outcomes.

Hypertension in metabolic syndrome: vascular pathophysiology

METABOLIC SYNDROME IS A CLUSTER OF METABOLIC AND CARDIOVASCULAR SYMPTOMS: insulin resistance (IR), obesity, dyslipemia. Hypertension and vascular disorders are central to this syndrome. After a brief historical review, we discuss the role of sympathetic tone. Subsequently, we examine the link between endothelial dysfunction and IR. NO is involved in the insulin-elicited capillary vasodilatation. The insulin-signaling pathways causing NO release are different to the classical. There is a vasodilatory pathway with activation of NO synthase through Akt, and a vasoconstrictor pathway that involves the release of endothelin-1 via MAPK. IR is associated with an imbalance between both pathways in favour of the vasoconstrictor one. We also consider the link between hypertension and IR: the insulin hypothesis of hypertension. Next we discuss the importance of perivascular adipose tissue and the role of adipokines that possess vasoactive properties. Finally, animal models used in the study of vascular function of metabolic syndrome are reviewed. In particular, the Zucker fatty rat and the spontaneously hypertensive obese rat (SHROB). This one suffers macro- and microvascular malfunction due to a failure in the NO system and an abnormally high release of vasoconstrictor prostaglandins, all this alleviated with glitazones used for metabolic syndrome therapy.

Vascular actions of aldosterone

Aldosterone exerts direct effects on the vascular system by inducing oxidative stress, inflammation, hypertrophic remodeling, fibrosis, and endothelial dysfunction. Aldosterone exerts its effects through genomic and nongenomic pathways in a mineralocorticoid receptor (MR)-dependent or independent manner. Other aldosterone receptors such as GPR30 have been identified. A tight relation exists between the aldosterone and angiotensin II pathways, as well as with the endothelin-1 system. There is a correlation between plasma levels of aldosterone and cardiovascular risk. Recently, an increasing body of evidence has underlined the importance of aldosterone in cardiovascular complications associated with the metabolic syndrome, such as arterial remodeling and endothelial dysfunction. Blockade of MR is an increasingly used evidence-based therapy for many forms of cardiovascular disease, including hypertension, heart failure, chronic kidney disease, and diabetes mellitus.

Mechanisms linking obesity to hypertension

Obesity-related hypertension is increasingly recognized as a distinct hypertensive phenotype requiring a modified approach to diagnosis and management. In this review rapidly evolving insights into the complex and interdependent mechanisms linking obesity to hypertension are discussed. Overweight and obesity are associated with adipose tissue dysfunction, characterized by enlarged hypertrophied adipocytes, increased infiltration by macrophages and marked changes in secretion of adipokines and free fatty acids. This results in chronic vascular inflammation, oxidative stress, activation of the renin-angiotensin-aldosterone system and sympathetic overdrive, eventually leading to hypertension. These mechanisms may provide novel targets for anti-hypertensive drug treatment. Recognition of obesity-related hypertension as a distinct diagnosis enables tailored therapy in clinical practice. This includes lifestyle modification and accommodated choice of blood pressure-lowering drugs.

Role of the Renin-Angiotensin system and aldosterone on cardiometabolic syndrome

Aldosterone facilitates cardiovascular damage by increasing blood pressure and through different mechanisms that are independent of its effects on blood pressure. In this respect, recent evidence involves aldosterone in the pathogenesis of metabolic syndrome. Although this relationship is complex, there is some evidence suggesting that different factors may play an important role, such as insulin resistance, renin-angiotensin-aldosterone system, oxidative stress, sodium retention, increased sympathetic activity, levels of free fatty acids, or inflammatory cytokines and adipokines. In addition to the classical pathway by which aldosterone acts through the mineralocorticoid receptors leading to sodium retention, aldosterone also has other mechanisms that influence cardiovascular tissue remodelling. Finally, overweight and obesity promote the adrenal secretion of aldosterone, increasing the predisposition to type 2 diabetes mellitus. Further studies are needed to better establish therapeutic strategies that act on the blockade of mineralocorticoid receptor in the treatment and prevention of cardiovascular diseases related to the excess of aldosterone and the metabolic syndrome.

The role of aldosterone in the metabolic syndrome

The metabolic syndrome associates metabolic abnormalities such as insulin resistance and dyslipidemia with increased waist circumference and hypertension. It is a major public health concern, as its prevalence could soon reach 30% to 50% in developed countries. Aldosterone, a mineralocorticoid hormone classically involved in sodium balance regulation, is increased in patients with metabolic syndrome. Besides its classic actions, aldosterone and mineralocorticoid receptor (MR) activation affect glucose metabolism, inducing insulin resistance through various mechanisms that involve oxidative stress, inflammation, and downregulation of proteins involved in insulin signaling pathways. Aldosterone and MR signaling exert deleterious effects on the cardiovascular system and the kidney that influence the cardiovascular risk associated with metabolic syndrome. Salt load plays a major role in cardiovascular injury induced by aldosterone and MR signaling. Large multicenter, randomized clinical trials testing the beneficial effects of MR antagonists on cardiovascular events and mortality in patients with metabolic syndrome are needed.

Type 2 diabetic patients with resistant hypertension should be screened for primary aldosteronism

BP control in diabetic patients is often poor. The contribution of secondary hypertension due to undiagnosed PA in hypertensive type 2 diabetic patients is not well studied. We prospectively screened 100 consecutive Asian type 2 diabetic patients with difficult-to-control or resistant hypertension for PA. PAC (pmol/L) to PRA (ng/mL/h) ratio was measured; those with PAC-to-PRA ratio >550 (corresponding PAC >415) underwent intravenous 0.9% SLT. Patients with PAC >/=140 following SLT had CT adrenals and bilateral AVS. Thirteen patients (13%) were confirmed to have PA, and all had resistant hypertension. Eight had a surgically correctable form of PA. Patients with PA had higher mean (SD) systolic [159.0 (10.6) vs. 146.0 (10.7) mmHg, p=0.001] and diastolic BP [94.6 (6.0) vs. 87.6 (5.9) mmHg, p=0.001], lower serum potassium [3.5 (0.6) vs. 4.3 (0.5) mmol/L, p=0.001], and higher PAC [679.3 (291.0) vs. 239.5 (169.4) pmol/L, p=0.001]. Identification and institution of definitive treatment for PA resulted in better BP control and in a reduction in the use of antihypertensive medications. Our findings demonstrate a high prevalence of PA in type 2 diabetic patients with resistant hypertension. Systematic screening for PA in this select group is recommended, as targeted treatment improves BP control.

Role of aldosterone and angiotensin II in insulin resistance: an update

The role of the Renin-Angiotensin-Aldosterone system (RAAS) on the development of insulin resistance and cardiovascular disease is an area of growing interest. Most of the deleterious actions of the RAAS on insulin sensitivity appear to be mediated through activation of the Angiotensin II (Ang II) Receptor type 1 (AT(1)R) and increased production of mineralocorticoids. The underlying mechanisms leading to impaired insulin sensitivity remain to be fully elucidated, but involve increased production of reactive oxygen species and oxidative stress. Both experimental and clinical studies also implicate aldosterone in the development of insulin resistance, hypertension, endothelial dysfunction, cardiovascular tissue fibrosis, remodelling, inflammation and oxidative stress. There is abundant evidence linking aldosterone, through non-genomic actions, to defective intracellular insulin signalling, impaired glucose homeostasis and systemic insulin resistance not only in skeletal muscle and liver but also in cardiovascular tissue. Blockade of the different components of the RAAS, in particular Ang II and AT(1)R, results in attenuation of insulin resistance, glucose homeostasis, as well as decreased cardiovascular disease morbidity and mortality. These beneficial effects go beyond to those expected with isolated control of hypertension. This review focuses on the role of Ang II and aldosterone in the pathogenesis of insulin resistance, as well as in clinical relevance of RAAS blockade in the prevention and treatment of the metabolic syndrome and cardiovascular disease.

Aldosterone and alterations of hypertension-related vascular function in African Americans

BACKGROUND

African Americans have a high prevalence of hypertension and hypertension-related vascular disease. We previously reported that plasma aldosterone concentrations are relatively high in hypertensive African Americans. This study evaluates the hypothesis that hypertension and hypertension-related alterations of peripheral vascular and renal vascular function are associated with aldosterone.

METHODS

Twenty four-hour blood pressures, cardiac output, renal blood flow (RBF), plasma renin activity (PRA), and plasma aldosterone were measured in hypertensive and normotensive African Americans. Hemodynamic measurements were repeated in response to graded infusions of norepinephrine (NE).

RESULTS

Ambulatory blood pressures in hypertensives and normotensives were 142 +/- 1/86 +/- 1 and 117 +/- 1/70 +/- 1 mm Hg, respectively. Cardiac index (CI) was lower (P < 0.01), peripheral vascular resistance was higher (P < 0.0001), arterial compliance was lower (P < 0.0001), RBF was lower (P = 0.04), and renal vascular resistance (RVR) was higher (P < 0.0001) in the hypertensives. Overall, blood pressures were positively correlated with peripheral vascular resistance (P < 0.0001) and inversely correlated with vascular compliance (P < 0.0001). In response to NE, hypertensives had greater increases of systolic blood pressure (P < 0.004) and pulse pressure (P < 0.005). PRA was lower (P < 0.0001) and plasma aldosterone was higher (P < 0.0001) in the hypertensives. Overall, blood pressures and pulse pressure were correlated with aldosterone (P < or = 0.01). Vascular compliance, RVR, and the increment of RVR in response to NE were also correlated with aldosterone (P < or = 0.03).

CONCLUSIONS

Aldosterone may contribute to hypertension and to hypertension-related alterations of peripheral vascular and renal vascular function in African Americans.

Plasma aldosterone and its relationships with left ventricular mass in essential hypertensive patients with the metabolic syndrome

BACKGROUND

The association of aldosterone with the metabolic syndrome (MetS) has not been fully elucidated. The aim of our study was to evaluate the relationships of plasma aldosterone concentration (PAC) with MetS and left ventricular mass (LVM) in nondiabetic Caucasian patients with essential hypertension.

METHODS

Measurements were taken with the patients off antihypertensive medications. The measurements included 24-h blood pressure (BP) readings, plasma renin activity (PRA) and aldosterone, and an echocardiogram.

RESULTS

Subjects with MetS (n = 201) had higher age-adjusted PAC (10.2 +/- 5.8 vs. 11.6 +/- 5.9 ng/dl; P = 0.01) and greater age-adjusted LVM indexed for height2.7 (LVMH2.7) (56 +/- 19 vs. 62 +/- 20 g/m2; P = 0.001) than those without MetS (n = 249). The difference in respect of PAC between the two groups was independent of PRA and was attributable mainly to obesity. After adjusting for potential confounders, LVMH2.7 was associated with MetS as a whole (beta = 0.11; P = 0.02) and with body mass index (BMI) (beta = 0.19; P < 0.0001) in the overall population. The latter relationship was attenuated (beta = 0.15; P = 0.001) after further adjustment for PAC. In the MetS group the association of LVMH2.7 with PAC held (beta = 0.19; P = 0.007) in multivariate analyses. In subjects without MetS, this relationship had only borderline statistical significance.

CONCLUSIONS

Our results suggest that the elevated PAC related to obesity may help to explain the increased LVM observed in association with MetS, and may contribute to enhancing the cardiovascular risk associated with MetS.

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.

Association of Adrenal Steroids With Hypertension and the Metabolic Syndrome in Blacks

Blacks have a high prevalence of hypertension and adrenal cortical adenomas/hyperplasia. We evaluated the hypothesis that adrenal steroids are associated with hypertension and the metabolic syndrome in blacks. Ambulatory blood pressures, anthropometric measurements, and measurements of plasma renin activity (PRA), aldosterone, fasting lipids, glucose, and insulin were obtained in 397 subjects (46% hypertensive and 50% female) after discontinuing antihypertensive and lipid-lowering medications. Hypertension was defined as average ambulatory blood pressure >130/85 mm Hg. Late-night and early morning salivary cortisol, 24-hour urine-free cortisol, and cortisone excretion were measured in a consecutive subsample of 97 subjects (40% hypertensive and 52% female). Compared with normotensive subjects, hypertensive subjects had greater waist circumference and unfavorable lipid profiles, were more insulin resistant, and had lower PRA and higher plasma aldosterone and both late-night and early morning salivary cortisol concentrations. Twenty-four-hour urine-free cortisol and cortisone did not differ. Overall, ambulatory blood pressure was positively correlated with plasma aldosterone (r=0.22; P<0.0001) and late-night salivary cortisol (r=0.23; P=0.03) and inversely correlated with PRA (r=-0.21; P<0.001). Plasma aldosterone correlated significantly with waist circumference, total cholesterol, triglycerides, insulin, and the insulin-resistance index. Based on Adult Treatment Panel III criteria, 17% of all of the subjects were classified as having the metabolic syndrome. Plasma aldosterone levels, but not PRA, were elevated in subjects with the metabolic syndrome (P=0.0002). The association of aldosterone with blood pressure, waist circumference, and insulin resistance suggests that aldosterone may contribute to obesity-related hypertension in blacks. In addition, we speculate that relatively high aldosterone and low PRA in these hypertensive individuals may reflect a mild variant of 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.

Nitric oxide opposes glucose-induced hypertension by suppressing sympathetic activity

We have reported that glucose infusion in L-NAME-treated rats increased arterial pressure more than the additive responses to glucose and L-NAME alone. This suggested that nitric oxide synthesis inhibition potentiated the hypertensive response to chronic glucose infusion, and the heart rate data suggested an important role for the sympathetic nervous system. This study tested the role of the sympathetic nervous system by infusing glucose for 7 days in 4 groups of rats: L-NAME (L), L-NAME plus alpha- and beta-adrenergic receptor blockade (LB), vehicle, or vehicle plus adrenergic receptor blockade (blockers). Mean arterial pressure (MAP, 24 hours per day) increased significantly in both the vehicle and blockers groups, confirming our previous reports. Likewise, MAP increased significantly more during glucose infusion in the L rats, from 120+/-3 mm Hg to 158+/-4 mm Hg by day 7, which was >3 times the increase in the vehicle rats. Heart rate also increased significantly in the L rats, from 391+/-4 to 426+/-8 bpm, and that increase was prevented completely in the LB rats. However, although the increase in MAP in the LB rats was significantly less than in the L rats, the hypertension was not prevented completely. The explanation for that partial inhibition is not clear, but the overall effectiveness of adrenergic receptor blockade to attenuate the potentiated hypertensive and tachycardic responses to glucose infusion in the L-NAME-treated rats versus the normal rats suggests that nitric oxide may help protect against hypertension during glucose infusion through suppression of sympathetic activity.

Serum aldosterone changes during hyperinsulinemia are correlated to body mass index and insulin sensitivity in patients with essential hypertension

OBJECTIVE

To measure the effects of hyperinsulinemia on serum electrolyte status and associated hormones, and on serum free fatty acid (FFA) concentrations, in patients with essential hypertension.

DESIGN AND METHODS

The serum electrolyte status (Na, K, Ca, ionized Ca, Mg, P, pH) and associated hormones [plasma renin activity (PRA), serum parathyroid hormone (PTH) and aldosterone concentrations], and FFA were measured during an euglycemic hyperinsulinemic clamp test in 49 patients with untreated essential hypertension.

RESULTS

Serum potassium, phosphate, PTH, and FFA concentrations decreased during hyperinsulinemia, while serum ionized calcium concentration, pH, and PRA increased significantly (P < 0.05). The changes in serum potassium and magnesium were both inversely related to the insulin-mediated glucose uptake (r= -0.62, P< 0.0001; r= -0.31, P< 0.05, respectively). Both body mass index (BMI) and insulin-mediated glucose disposal were significantly correlated to the changes in serum aldosterone concentration during hyperinsulinemia (r = 0.41, P < 0.01; r = -0.40, P < 0.01, respectively). The change in serum aldosterone during the clamp test was not significantly related to the change in PRA, but tended to correlate to the change in potassium concentration (r= 0.25, P= 0.10). A less pronounced reduction in FFA during induced hyperinsulinemia was associated with low insulin sensitivity (r= -0.35, P< 0.05).

CONCLUSION

Hypertensive patients with normal BMI and a more pronounced glucose uptake showed a larger serum potassium decline and lowered aldosterone concentrations during induced euglycemic hyperinsulinemia. Insulin-resistant patients showed a less pronounced reduction in FFA during hyperinsulinemia. The observations in the present study may indicate that alterations in aldosterone and FFA metabolism might be linked to the insulin resistance metabolic syndrome.

Adrenocortical imprint in the fetus of a diabetic gestation

Offspring of diabetics are at increased risk for diabetes as adults. As corticosteroids are intimately involved in glucose homeostasis, we investigated aspects of corticosteroid activity in the late gestation fetuses of control, moderately diabetic and insulin-controlled streptozotocin-induced diabetic rats. We found that moderate maternal diabetes had no effect upon litter size or fetal body weight. Uncontrolled maternal diabetes was accompanied by fetal hyperglycemia, hyperinsulinemia and elevated aldosterone. Maternal insulin treatment normalized fetal glucose and aldosterone; fetal insulin and corticosterone levels increased. Maternal diabetes had no effect upon fetal adrenal expression of P450scc mRNA; the abundance of P450c11beta mRNA increased, and returned to that of the control gestation upon insulin treatment. P450c11AS mRNA was barely detectable, and decreased in the fetuses of insulin-treated diabetics. P450c11B3 mRNA was undetectable in all fetal groups. Our results implicate aspects of maternal diabetes in the expression of a fetal adrenocortical imprint, manifested as a greater abundance of P450c11beta mRNA. Although not accompanied by elevated corticosterone in the fetus, this imprint could ultimately allow for greater potential corticosterone production in response to typical stimuli, and thus contribute to the tendency towards glucose dysregulation in these offspring of diabetic gestations.

Visceral obesity and insulin resistance are associated with plasma aldosterone levels in women

OBJECTIVE

Both obesity and insulin resistance increase the risk of hypertension and other cardiovascular diseases, but the mechanisms linking these abnormalities are unknown. The current study was undertaken to examine the effects of obesity, fat distribution, and insulin resistance on plasma levels of aldosterone and other adrenal steroids that might contribute to sequelae of obesity.

RESEARCH METHODS AND PROCEDURES

Twenty-eight normotensive premenopausal women and 27 normotensive men with a wide range of body fat underwent measurements of visceral adipose tissue by CT scan, total fat mass by dual energy X-ray absorptiometry, blood pressure, insulin sensitivity, and plasma levels of three adrenal steroid hormones.

RESULTS

Plasma aldosterone in women correlated directly with visceral adipose tissue (r=0.66, p<0.001) and inversely with insulin sensitivity (r=-0.67, p<0.001), and these associations were independent of plasma renin activity. There were no corresponding correlations in men. Plasma aldosterone was significantly correlated with plasma cortisol and dehydroepiandrosterone sulfate in women. Seventeen women and 15 men completed a weight-reduction regimen, losing an average of 15.1+1.2 kg. After weight loss, plasma aldosterone was significantly lower and insulin sensitivity higher; however, the correlations of aldosterone with visceral adipose tissue and insulin sensitivity in women persisted (p = 0.09 and 0.07, respectively). Although none of the women were hypertensive, blood pressure correlated with plasma aldosterone both before and after weight loss.

DISCUSSION

We conclude that visceral adiposity and insulin resistance are associated with increased plasma aldosterone and other adrenal steroids that may contribute to cardiovascular diseases in obese women.

Insulin-induced renal dysfunction in regular Sabra rats

1. We tested the effects of chronic hyperinsulinaemia on renal function. Hyperinsulinaemia, in the range of 1.5-4 times the control levels, was achieved using a sustained-release insulin implant. Sham-treated rats served as controls. 2. Experiment 1. Acute saline loading: seven sham and seven hyperinsulinaemic rats received an acute saline load (4 mL/100 g). Two h post-load urea and creatinine excretion rats were (mu mol/min) 15 +/- 5 and 9 +/- 4, and 0.17 +/- 0.05 and 0.10 +/- 0.04, respectively; P < 0.05 for both. 3. Experiment 2. Chronic saline loading: 12 sham- and 24 insulin-treated rats drank saline for 8 weeks plus 4% NaCl in the food for 2 more weeks. By week 10 plasma creatinine (mu mol/L) was 62 +/- 12 and 78 +/- 13, and creatinine clearance (mL/min) was 1.9 +/- 0.5 and 1.5 +/- 0.4, respectively; P < 0.05 for both. 4. Experiment 3. Regular diet: 10 sham- and 14 insulin-treated rats had, by week 8, plasma creatinine (mu mol/L) of 75 +/- 34 and 96 +/- 37 and creatinine clearance (mL/min) of 1.260 +/- 0.025 and 0.97 +/- 0.22, respectively; P < 0.02 for both. Bodyweight, resting blood pressure and urinary Na+ and K+ excretion were comparable in sham- and insulin-treated rats. 5. In three experimental settings long-term hyperinsulinaemia was associated with a subtle but significant renal dysfunction. This finding may be related to the aetiology of renal complications of hypertension and diabetes mellitus, both of which are insulin-resistant and hyperinsulinaemic states.

Relationships among plasma aldosterone, high-density lipoprotein cholesterol, and insulin in humans

To investigate the pathogenesis of hypertension in patients with obesity and insulin resistance and to explore the role of plasma lipids, we studied 30 subjects at the end of 7 days of low (20 mEq/d) then high (200 mEq/d) sodium diets. Glucose and insulin tolerance tests were performed at the end of each week and blood and urine collected for measurements of plasma aldosterone, renin activity, electrolytes, insulin, and lipoproteins. There was a strong negative correlation between plasma aldosterone and high-density lipoprotein cholesterol during both diets. There were weaker positive correlations between plasma aldosterone and insulin or triglycerides. When the aldosterone-renin ratio was the dependent variable and the correlation controlled for serum potassium, the inverse relationship with high-density lipoprotein cholesterol and the positive correlation with insulin remained, but only during the high salt diet. Subjects were divided into three groups based on high-density lipoprotein cholesterol. Subjects with the lowest high-density lipoprotein cholesterol levels showed the highest aldosterone, plasma triglycerides, body mass index, and waist-to-hip ratio. Those subjects also demonstrated the greatest resistance to insulin action on glucose and plasma unesterified fatty acids. There was a weak direct correlation between plasma aldosterone and systolic blood pressure during the high salt diet. These data suggest that high aldosterone levels may be a link between dyslipidemia, insulin resistance, and hypertension, a relationship made more evident by high salt intake.

Differential short- and long-term effects of insulin on ANG II action in human adrenal glomerulosa cells

Insulin is known to modulate several functions in bovine adrenal cells, including steroidogenesis and growth. However, the role of insulin in regulating aldosterone synthesis in human adrenal glomerulosa cells has not been studied. In the present studies, we have examined the acute and chronic effects of insulin on angiotensin II (ANG II)-induced aldosterone synthesis in cultured normal and adenomatous human adrenal glomerulosa cells. Short-term insulin treatment (1.5 h) resulted in inhibition of ANG II-induced aldosterone synthesis. In contrast, chronic treatment (30 h) resulted in potentiation of ANG II action. The 12-lipoxygenase pathway of arachidonate metabolism has been shown to play a key role in ANG II-induced aldosterone synthesis. The acute inhibitory effects of insulin were in part mediated by inhibition of the 12-lipoxygenase pathway. The chronic stimulatory effect of insulin seemed to be due at least in part to the upregulation of cytochrome P-450 side-chain cleavage enzyme levels. These findings suggest that insulin has a differential temporal effect on ANG II action and therefore may be an important regulator of ANG II-induced aldosterone synthesis in the adrenal.