Influence of systemic arterial blood pressure and nonhemodynamic factors on the brachial artery pulsatility index in mild to moderate essential hypertension

The risks and benefits of aldosterone antagonists

Spironolactone and eplerenone are mineralocorticoid- blocking agents used for their ability to block a host of epithelial and nonepithelial actions of aldosterone. These compounds are of proven benefit in reducing blood pressure and urine protein excretion, and in conferring cardiovascular gain in diverse circumstances of heart failure. However, as enthusiasm grows for use of mineralocorticoid-blocking agents, the risks inherent to use of such drugs become more pertinent. Whereas the endocrine side effects of spironolactone are in reality little more than a cosmetic disfigurement, the potassium-sparing properties of spironolactone and eplerenone can prove life-threatening if hyperkalemia develops. However, for most patients the risk of developing hyperkalemia should not dissuade the prudent clinician from use of these compounds. Hyperkalemia should be considered as a possibility in any patient receiving these medications and as such is best addressed preemptively.

Aldosterone target organ protection by eplerenone

The classical mineralocorticoid effect of aldosterone on unidirectional transepithelial sodium transport in the kidney was long thought to be the predominant effect of this hormone. However, there is convincing evidence for additional extrarenal actions of aldosterone that are mediated via activation of mineralocorticoid receptors (MRs) in the heart, vasculature and brain. It is now postulated that many of the detrimental effects of aldosterone are mediated through MR activation in these nonclassical target organs. The selective aldosterone blocker, eplerenone (Inspra), is under development for human therapeutic use for treatment of hypertension and heart failure post-myocardial infarction (MI). Clinical and preclinical studies have linked elevated aldosterone to hypertension, left ventricular and vascular remodeling, cardiac, renal, and cerebral vascular inflammation and injury, and increased risk of mortality in heart failure patients. Multiple studies in experimental models of hypertension and heart failure demonstrate that selective blockade of aldosterone by eplerenone effectively preserves cardiac function, attenuates maladaptive left ventricular remodeling and tissue and vascular injury in part by reducing vascular inflammation in aldosterone target organs.

Transgenic model of aldosterone-driven cardiac hypertrophy and heart failure

Aldosterone classically promotes unidirectional transepithelial sodium transport, thereby regulating blood volume and blood pressure. Recently, both clinical and experimental studies have suggested additional, direct roles for aldosterone in the cardiovascular system. To evaluate aldosterone activation of cardiomyocyte mineralocorticoid receptors, transgenic mice overexpressing 11beta-hydroxysteroid dehydrogenase type 2 in cardiomyocytes were generated using the mouse alpha-myosin heavy chain promoter. This enzyme converts glucocorticoids to receptor-inactive metabolites, allowing aldosterone occupancy of cardiomyocyte mineralocorticoid receptors. Transgenic mice were normotensive but spontaneously developed cardiac hypertrophy, fibrosis, and heart failure and died prematurely on a normal salt diet. Eplerenone, a selective aldosterone blocker, ameliorated this phenotype. These studies confirm the deleterious consequences of inappropriate activation of cardiomyocyte mineralocorticoid receptors by aldosterone and reveal a tonic inhibitory role of glucocorticoids in preventing such outcomes under physiological conditions. In addition, these data support the hypothesis that aldosterone blockade may provide additional therapeutic benefit in the treatment of heart failure.

Aldosterone and vascular damage

Although the aldosterone escape mechanism is well known, aldosterone has often been neglected in the pathophysiologic consequences of the activated renin-angiotensin-aldosterone system in arterial hypertension and chronic heart failure. There is now evidence for vascular synthesis of aldosterone aside from its secretion by the adrenal cortex. Moreover, aldosterone is involved in vascular smooth muscle cell hypertrophy and hyperplasia, as well as in vascular matrix impairment and endothelial dysfunction. The mechanisms of action of aldosterone may be either delayed (genomic) or rapid (nongenomic). Deleterious effects of aldosterone leading to vascular target-organ damage include (besides salt and water retention) decreased arterial and venous compliance, increased peripheral vascular resistance, and impaired autonomic vascular control due to baroreflex dysfunction.

Hypertensive left ventricular hypertrophy: pathophysiology, assessment and treatment

Left ventricular hypertrophy (LVH) is a strong predictor of cardiovascular morbidity and mortality. LVH is associated with coronary events, and there is an association between cerebrovascular disease and increased left ventricular mass (LVM). Experimental studies have elucidated the importance of non-myocytic cells inducing increased perivascular and interstitial fibrosis along with thickening of the media of intramyocardial coronary arteries in hypertensive LVH. M-mode echocardiography is the most accepted standard for the diagnosis and quantification of LVH, but some controversies exist regarding the ideal methodology for serial assessment of LVM. It is still a matter of debate whether 2-dimensional echo measurements represent a more accurate method. Hopefully, both the introduction of 3-dimensional echo and new Doppler techniques can provide more accurate measurements of LVM and additional information on changes in myocardial fibrosis and stiffness. Experimental studies have shown that normalization of hypertensive myocardial and coronary artery remodelling take place with drugs like angiotensin converting enzyme (ACE)-inhibitors and calcium antagonists. Two meta-analyses suggest that ACE-inhibitors may be the most efficient drugs in reducing LVM, but a clinical correlate to this assumption is at present not available. There are some indications that regression or progression of LVH assessed by ECG and echocardiography may in fact be related to the incidence of cardiovascular events. But large-scale controlled studies of various treatment regimens are still needed to establish whether drug induced regression can improve the prognosis of hypertensive LVH independent of the antihypertensive effect.