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

Aldosterone and aldosterone antagonism in cardiovascular disease: focus on eplerenone (Inspra)

Aldosterone has long been known to mediate water and electrolyte balance by acting on mineralocorticoid receptors in the kidneys. However, recent studies have demonstrated the presence of these receptors in nonclassical locations, including the brain, blood vessels, and the heart. This finding suggests that aldosterone may play a larger role than once appreciated in normal physiologic function and cardiovascular disease. Some of the adverse cardiovascular effects that have been described include cardiac and vascular fibrosis, left ventricular hypertrophy, congestive heart failure, hypertension, endothelial dysfunction, reduced fibrinolysis, and cardiac arrhythmias. In light of these findings, aldosterone receptor blockers have become increasingly more important. This is especially true considering the fact that traditional therapies, such as angiotensin-converting enzyme inhibitors and angiotensin II-receptor blockers, may not be effective in maintaining long-term suppression of aldosterone. Therefore, a great deal of focus has been placed on spironolactone, which has proven to be an effective, albeit nonselective, aldosterone receptor blocker. The Randomized Aldactone Evaluation Study has shown that spironolactone results in a 30% reduction in mortality among patients with severe congestive heart failure. Other studies have shown spironolactone to lower high blood pressure, improve endothelial dysfunction, reduce left ventricular hypertrophy, and lower the incidence of fatal arrhythmias. However, spironolactone, because of its interaction with other steroid receptors, is not without its limitations, which include gynecomastia, breast tenderness, menstrual irregularities, and impotence. As a result, eplerenone (INSPRA), a selective aldosterone blocker, is currently being investigated for its efficacy and side-effect profile compared with spironolactone. Eplerenone has already been approved for the treatment of systemic hypertension, and several clinical trials are currently underway to identify other therapeutic uses for this agent in cardiovascular disease management.

Insulin, renin-aldosterone system and blood pressure in obese people

OBJECTIVE

To evaluate the relationship between insulin, the renin-aldosterone system and blood pressure in obese subjects.

DESIGN AND METHODS

A cross sectional study of a group of severely obese normotensive subjects who were surgical candidates (n=39; mean BMI: 47.8+/-1.4) and a group of hypertensive patients (n=57; mean BMI: 28.0+/-0.7) twenty-nine of whom had BMI>27. All subjects were studied after 15 days on a balanced diet. Insulin, plasma renin activity and aldosterone were measured.

RESULTS

Fasting insulin, plasma renin activity and aldosterone were higher in severely obese normotensive subjects than in hypertensive subjects (respectively 32.3+/-3.0 vs 13.1+/-1.0 mU/l, P=0.0001; 1.34+/-0.22 vs 0.88+/-0.12 ng/ml/h, P=0.04; 137.2+/-16.2 vs 87.9+/-12.1 pg/ml, P=0.015). Insulin was related to BMI and to aldosterone both in normotensive and in hypertensive patients.

CONCLUSION

Hyperinsulinemia itself does not determine hypertension; in some people it could play a vasodilator role in opposition to the renin-aldosterone system.

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.

Use of statins and blood pressure control in treated hypertensive patients with hypercholesterolemia

High serum cholesterol has been frequently reported in patients with arterial hypertension in whom it might influence the blood pressure control. The aim of this study was to compare the extent of blood pressure changes in 41 patients with hypertension and hypercholesterolemia, taking antihypertensive drugs and treated for 3 months with statins (HC-S; pravastatin or simvastatin) and compared with matched controls with high (HC-D; 44) or normal serum cholesterol (NC-D; 45) undergoing antihypertensive treatment combined with dietary treatment alone. After 3 months of follow-up, a greater reduction of systolic (SBP) and diastolic (DBP) blood pressure values was observed in HC-S patients (ASBP/DBP, -11.3 +/-3/-10.6 +/- 2%) when compared with both HC-D (deltaSBP/DBP, -6.6 +/- 2/-6.1 +/- 2%; p < 0.05) and NC-D (deltaSBP/DBP, -6.9 +/- 2/-6.8 +/- 1.5%; p < 0.05). In statin-treated patients, a slight linear relation has been found between the percentage changes in DBP and those in plasma total cholesterol (R = 0.37, p = 0.043), whereas no relation was found with SBP changes (R =0.11; p = 0.35). In conclusion, the results of this study demonstrate that the use of statins in combination with antihypertensive drugs can improve blood pressure control in patients with uncontrolled hypertension and high serum cholesterol levels. The additional blood pressure reduction observed in patients treated with statins is clinically relevant and only partially related to the lipid-lowering effect.

Synergistic effect of adrenal steroids and angiotensin II on plasminogen activator inhibitor-1 production

Recent data suggest an interaction between the renin-angiotensin-aldosterone system and fibrinolysis. Although previous work has focused on the effect of angiotensin II (Ang II) on plasminogen activator inhibitor (PAI-1) expression, the present study tests the hypothesis that aldosterone contributes to the regulation of PAI-1 expression. To test this hypothesis in vitro, luciferase reporter constructs containing the human PAI-1 promoter were transfected into rat aortic smooth muscle cells. Exposure of the cells to 100 nmol/L Ang II resulted in a 3-fold increase in luciferase activity. Neither 1 micromol/L dexamethasone nor 1 micromol/L aldosterone alone increased PAI-1 expression. However, both dexamethasone and aldosterone enhanced the effect of Ang II in a dose-dependent manner. This effect was abolished by mutation in the region of a putative glucocorticoid-responsive element. A similar interactive effect of Ang II and aldosterone was observed in cultured human umbilical vein endothelial cells. The time course of the effect of aldosterone on Ang II-induced PAI-1 expression was consistent with a classical mineralocorticoid receptor mechanism, and the effect of aldosterone on PAI-1 synthesis was attenuated by spironolactone. To determine whether aldosterone affected PAI-1 expression in vivo, we measured local venous PAI-1 antigen concentrations in six patients with primary hyperaldosteronism undergoing selective adrenal vein sampling. PAI-1 antigen, but not tissue plasminogen activator antigen, concentrations were significantly higher in adrenal venous blood than in peripheral venous blood. Taken together, these data support the hypothesis that aldosterone modulates the effect of Ang II on PAI-1 expression in vitro and in vivo in humans.

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.

Plasma aldosterone, plasma lipoproteins, obesity and insulin resistance in humans

Aldosterone production in vitro can be affected by many hormones, autacoids, ions, and lipids, but regulation in humans is incompletely understood. We measured plasma aldosterone in adult subjects with a wide range of obesity and insulin resistance. Aldosterone levels correlated with measures of visceral obesity in one predominantly male cohort and in the women of a second cohort. In the same subjects, aldosterone correlated with insulin resistance. Aldosterone also correlated with plasma cortisol in men and women, and with DHEA-S in women. The data suggested that visceral fat stimulates adrenal steroidogenesis. We found that certain fatty acids stimulated aldosterone production in vitro by rat adrenal cells incubated with rat hepatocytes, but not adrenal cells alone. The results suggested that fatty acids from visceral adipocytes induce hepatic formation of an adrenal secretagogue. This may explain the correlation of plasma steroids with visceral obesity. Aldosterone may contribute to vascular diseases that complicate obesity.

Can Excess Glucocorticoid, Predispose to Cardiovascular and Metabolic Disease in Middle Age?

For many years, both human and animal studies correlated changes in behaviour of the young offspring with the degree of maternal stress or glucocorticoid exposure of the foetus/neonate. In the past ten years there has been overwhelming epidemiological evidence to suggest that growth retardation in utero is a very important risk factor for the development of cardiovascular and metabolic disease in adult life. More recently, it has been shown that one important, even key, determinant is the exposure of the foetus to excess glucocorticoid. Even a brief period (48 h) of dexamethasone exposure very early in pregnancy was able to programme permanently hypertensive adult sheep. Understanding how such programming works, and the underlying physiological changes that occur, provides one of the most exciting challenges in contemporary endocrinology and developmental biology.

Aldosterone in obesity

Plasma aldosterone levels were measured in adults whose body mass index ranged from lean to obese. Blood was drawn while subjects rested supine for 30-90 minutes. Aldosterone was higher in obese subjects, but could not be explained by renin or K+. The best predictors of plasma aldosterone were abdominal obesity measured as waist/hip ratio or by CT scan, and insulin resistance measured by insulin or oral glucose tolerance tests, or euglycemic clamp. In one cohort, these correlations were limited to women; in the other, they were also found in men. In the women with a strong correlation between aldosterone and visceral fat, aldosterone also correlated with cortisol and DHEA-S. The data are consistent with an effect of visceral fat on adrenal steroidogenesis. Visceral adipocytes have a high rate of triglyceride turnover, and their circulation drains directly to the liver. In an experiment based on these characteristics, rat hepatocytes responded to fatty acids by releasing an unidentified secretagogue that stimulated aldosterone production by rat adrenal glomerulosa cells. The clinical data suggest that aldosterone participates in hypertension associated with the "Insulin Resistance Syndrome". The adrenal in viscerally obese subjects may be driven by a secretagogue released from the liver by fatty acids from abdominal adipocytes.