Aldosterone to Renin ratio in a primary care setting: the Bussolengo study

Urinary Prostasin

Prostasin is a serine peptidase hypothesized to regulate epithelial sodium channel (ENaC) activity in animals or on in vitro cultured cells. We investigated whether urinary prostasin may be a candidate marker of ENaC activation in humans. We studied 10 healthy volunteers and 8 hypertensive patients with raised aldosterone-to-renin ratio before and after spironolactone or saline/Florinef suppression test, respectively. Four healthy subjects were also studied before and after saline. Urinary prostasin was evaluated by SDS-PAGE, 2D maps, and Western blotting. Every sample of normotensive individuals was compared with the corresponding sample of urine collected after spironolactone or saline; every sample of hypertensive patients was compared with the corresponding sample of urine collected after saline or Florinef. Prostasin was detectable in all subjects regardless of gender, dietary sodium intake, and spironolactone treatment. Spironolactone (100 mg) increased urinary Na+/K+ ratio and decreased urinary prostasin in normotensives in whom the renin/aldosterone axis was activated by a low Na+ intake, but it was ineffective in individuals with high Na+ intake. Saline infusion also reduced prostasin in normotensive subjects. In contrast, prostasin paradoxically increased in urine of patients affected by primary aldosteronism after volume expansion. By 2D immunoblotting, several protein isoforms were observed, some of them being overexpressed after inhibition tests in patients with primary aldosteronism. In addition to a "basal" aliquot of prostasin, constitutively released in human urine regardless of sodium balance and aldosterone activation, there exists a second "aldosterone-responsive" aliquot modulated by Na+ intake and potentially suitable as candidate marker of ENaC activation.

Diagnosis of primary aldosteronism: from screening to subtype differentiation

Numerous studies conducted in recent years have reported an increase in the prevalence of primary aldosteronism (PA). This increase has arisen because of changes in our screening methods used to detect PA, notably the widespread use of the ratio of plasma aldosterone concentration to plasma renin activity. A positive screening result, however, is not diagnostic and requires a confirmatory test. Strategies for screening and confirmation of PA and the techniques to identify the two main subtypes of PA--aldosterone-producing adenoma (APA) and bilateral adrenal hyperplasia (BAH)--are particularly important because hypertension in APA can be cured by adrenalectomy, whereas individuals affected with BAH can receive targeted medical treatment with mineralocorticoid receptor antagonists.

Aldosterone as a cardiovascular risk factor

Aldosterone exerts cardiovascular effects by influencing epithelial fluid and electrolyte excretion, and thus blood volume and pressure. Mineralocorticoid receptors (MR) are found in epithelial and non-epithelial tissues (vessel walls, heart, brain), with high affinity for aldosterone and physiological glucocorticoids cortisol and corticosterone. MR blockade by spironolactone or eplerenone favorably affects cardiovascular outcomes. In some situations (primary aldosteronism, experimental mineralocorticoid administration) activation of cardiovascular MR reflects aldosterone levels inappropriate for salt status. In others (heart failure, essential hypertension) aldosterone and Na(+) status are often normal pretreatment; cardiovascular MR may thus be activated by normal glucocorticoid levels after tissue damage and reactive oxygen species generation. Therefore, although unilateral adrenalectomy is preferred therapy for unilateral aldosterone-producing adenoma or hyperplasia, MR blockade may be useful in cardiovascular diseases where aldosterone levels are normal.

Low renin hypertensive states: perspectives, unsolved problems, future research

Some causes of low renin hypertension are familial with known genetic bases. One of them, primary aldosteronism, is specifically treatable by mineralocorticoid receptor blockers or by surgery, and has at least two different familial varieties. These have provided insights into its natural history, with long normotensive and normokalemic phases, and variable expression within the same family. Primary aldosteronism was considered rare, but recent work beginning in 1992 suggests that it might be the most common curable cause of hypertension, worth screening for in every hypertensive. Evidence is now compelling that inappropriate aldosterone for salt status can cause not only hypertension, but vascular inflammation and end-organ damage, preventable by mineralocorticoid receptor blockade.

RALES, EPHESUS and redox

In RALES, low doses of the mineralocorticoid receptor (MR) antagonist spironolactone, added to standard of care for severe heart failure, improved survival by 30% and lowered hospitalization by 35%. Animal studies with the selective MR antagonist eplerenone have similarly shown MR blockade to prevent the cerebral, renal and coronary vascular inflammatory response to elevated aldosterone levels. There is now general acceptance that aldosterone concentrations inappropriate for salt status have major deleterious effects on the cardiovascular system. In many instances, however (e.g. Randomized Aldactone Evaluation Study (RALES), EPHESUS) aldosterone levels are normal and salt status unremarkable and yet MR blockade has unquestioned benefits. In these instances, there is increasing evidence that coronary and cardiac MR are activated by normal circulating cortisol levels, in the cellular context of generation of reactive oxygen species (ROS) and/or alteration in intracellular redox status. MR in VSMC and cardiomyocytes are normally predominantly occupied by cortisol in tonic inhibitory mode. Blockade of 11beta hydroxysteroid dehydrogenase type II (11betaHSD2) or ROS generation both serve to activate cortisol-MR complexes, thus mimicking the effects of mineralocorticoid/salt imbalance on blood vessels and the heart. In RALES and EPHESUS, it is likely that the antagonists are blocking normal levels of cortisol, not aldosterone, from activating MR in the context of tissue damage and ROS generation. If this is the case, MR antagonists may be of wide therapeutic potential in cardiovascular disease and not confined to those characterized by aldosterone/salt excess. Finally, the pathophysiologic roles of always-occupied MR in 'unprotected' tissues such as cardiomyocytes or neurons in response to altered intracellular redox status remain to be explored.

Eplerenone: a review of its use in essential hypertension

Eplerenone is a selective aldosterone blocker (SAB) approved for the treatment of essential hypertension. Oral eplerenone reduced BP effectively in patients with essential hypertension, both as monotherapy and in combination with other agents. The drug is generally well tolerated; the risk of hyperkalemia can be managed through careful selection and monitoring of patients. Preliminary data suggest that treatment of hypertension with eplerenone may provide protective effects against end-organ disease; further work is needed to elucidate the clinical significance of these findings, and to evaluate the outcome of treatment of hypertension in terms of cardiovascular morbidity and mortality and quality of life. In the meantime, as the first SAB to become available, eplerenone is an interesting addition to the drugs currently available for the treatment of hypertension.

The syndromes of low-renin hypertension: "separating the wheat from the chaff"

Primary aldosteronism (PA) is characterized by hypertension and suppressed renin activity with or without hypokalemia and comprises the aldosterone-producing adenoma (APA) and bilateral adrenal hyperplasia or idiopatic hyperaldosteronism (IHA). In recent series employing the aldosterone (aldo, ng/dL):renin (ng/mL·h) ratio (ARR) for screening, prevalence of PA among hypertensives soars to 8-20%; current predominance of IHA (>80%) over APA suggests the inclusion of former low-renin essential hypertensives (LREH), in whom plasma aldo can be reduced by suppressive maneuvers. We evaluated the test characteristics of the ARR obtained retrospectively from 127 patients with PA (81 APA; 46 IHA) and 55 with EH (30 LREH; 25 NREH) studied from 1975 to 1990. Using the combined ROC-defined cutoffs of 27 for the ARR and 12ng/dL for aldo, we obtained 89.8% sensitivity (Ss) and 98.2% specificity (Sp) in discriminating PA from EH: all APA and 72% of the IHA patients had values above these limits, but only one (3%) with LREH. Among the 46 IHA patients, 10 (21.7%) had ARR <27, four of whom with aldo <12ng/dL, virtually indistinguishable from LREH. Use of higher cutoff values (ARR >100; aldo >20) may attain 84%Ss and 82.6%Sp in separating APA from IHA. Because IHA and LREH ("the chaff") may be spectrum stages from the same disease, definite discrimination between these entities seems immaterial. However, precise identification of the APA ("the wheat") is critical, since it is the only surgically curable form of PA. Thus, while patients who may harbor an APA must be thoroughly investigated and surgically treated, non-tumoral disease (IHA and LREH) may be best treated with an aldo-receptor antagonist that will also prevent the aldo-mediated inflammatory effects involved in myocardial fibrosis and abnormal cardiac remodeling.