The use of spironolactone in the diagnosis and the treatment of hypertension associated with mineralocorticoid excess

The pharmacological treatment of primary aldosteronism

Aldosterone is increasingly considered to have a fundamental role in the pathophysiology of cardiovascular disease. Primary aldosteronism is a much more common cause of secondary hypertension than once suspected, accounting for approximately 10% of cases. Screening for primary aldosteronism should be considered even in the presence of normokalaemia. The non-classical effects of aldosterone, some of which are transcription-independent, may be of similar or greater importance than its traditional effects on the kidney. Treatment of primary aldosteronism should be specific and aim to ameliorate all hormone-related effects of aldosterone, not just the most obvious manifestation of hypertension. Mineralocorticoid antagonism, shown to lead to significant additional survival advantage in heart failure, offers the best prospect for achieving therapeutic goals. For the increasing proportion of patients with primary aldosteronism suitable for long-term medical treatment, mineralocorticoid receptor blockade (better tolerated with eplerenone) should be considered the most appropriate choice of treatment, pending the development of better alternatives.

The 45-year story of the development of an anti-aldosterone more specific than spironolactone

At the early stage of its development in 1957, the daily dose of spironolactone necessary to improve various pathological conditions was not precisely determined and dose-dependent sexual side effects limited its long-term use. Prescription of high daily doses and absence of selectivity for the mineralocorticoid receptor explain these limitations. The 9-11alpha epoxy group added to mexrenone by the Ciba-Geigy chemists in 1984 and improved chemical synthesis at Searle, permitted the original international clinical development of a selective antagonist for high blood pressure and congestive heart failure treatment. This review deals with the main methodological issues of a 20-year biological and clinical development of eplerenone, the second antimineralocorticoid drug. The investigation of a large range of daily doses (25-400mg) initially selected in normal volunteers by the 9alpha-fluorohydrocortisone test has led to the conclusion that 50-100mg q.i.d. doses of eplerenone offer a favorable benefit/risk ratio in various patient populations by neutralization of the aldosterone effects on blood pressure and target organ damage. The absence of sexual side-effects has confirmed the clinical relevance of the initial biological hypothesis on the need for more selectivity at the androgen and progestogen receptor sites. Widening the distance between efficacy and adverse effects of an anti-mineralocorticoid drug will facilitate the long-term maintenance of a moderately negative sodium balance and a slightly positive potassium balance, while minimizing the direct effects of salt and aldosterone on the heart, vessels, brain, and kidneys. Wide use in unselected patients and additional controlled clinical trials are necessary to confirm the benefits expected from animal and clinical research given that a 45-year interval also characterizes the story of the Na-Cl cotransporter (NCC) blocker, chlorthalidone, from its initial clinical use to the demonstration of its beneficial effects on cardiovascular morbidity and mortality.

General overview of mineralocorticoid hormone action

The adrenal cortex elaborates two major groups of steroids that have been arbitrarily classified as glucocorticoids and mineralocorticoids, despite the fact that carbohydrate metabolism is intimately linked to mineral balance in mammals. In fact, glucocorticoids assured both of these functions in all living cells, animal and photosynthetic, prior to the appearance of aldosterone in teleosts at the dawn of terrestrial colonization. The evolutionary drive for a hormone specifically designed for hydromineral regulation led to zonation for the conversion of 18-hydroxycorticosterone into aldosterone through the catalytic action of a synthase in the secluded compartment of the adrenal zona glomerulosa. Corticoid hormones exert their physiological action by binding to receptors that belong to a transcription factor superfamily, which also includes some of the proteins regulating steroid synthesis. Steroids stimulate sodium absorption by the activation and/or de novo synthesis of the ion-gated, amiloride-sensitive sodium channel in the apical membrane and that of the Na+/K+-ATPase in the basolateral membrane. Receptors, channels, and pumps apparently are linked to the cytoskeleton and are further regulated variously by methylation, phosphorylation, ubiquination, and glycosylation, suggesting a complex system of control at multiple checkpoints. Mutations in genes for many of these different proteins have been described and are known to cause clinical disease.

Spironolactone: a re-examination

A review of the aldosterone antagonist spironolactone is presented. It is effective both as monotherapy and in combination with other hypotensive agents in the control of both essential and hyperaldosterone-induced hypertension. It is useful as a diuretic in conditions such as cirrhosis and congestive heart failure, and is most commonly employed because of its potassium- and magnesium-sparing qualities. Spironolactone also has been used as an antiandrogenic agent in managing hirsutism. Its adverse effect profile, considered somewhat prohibitive in the past, is generally not significant when reasonably low doses (less than 150 mg/d) are used.

Adrenal mitochondrial metabolism of spironolactone. Absence of metabolic activation

Previous investigations have established that spironolactone (SL) administration to guinea pigs decreases adrenal mitochondrial and microsomal cytochrome P-450 content, and that the latter requires microsomal activation of the drug. Studies were carried out to determine if adrenal mitochondrial metabolism (activation) of SL was similarly involved in the effects of the drug on mitochondrial cytochrome P-450 destruction. Incubation of guinea pig adrenal mitochondria with SL in the absence of NADPH resulted in the formation of 7 alpha-thio-SL as the only metabolite. In the presence of an NADPH-generating system, an unknown polar metabolite was also produced. The mass spectrum of the unknown compound suggested that it was a hydroxylated derivative of SL. Incubation of mitochondrial preparations with 7 alpha-thio-SL also resulted in the formation of a polar metabolite, but the latter had a different HPLC retention time than that of the SL metabolite. Formation of the polar SL metabolite was prevented by metyrapone, an 11 beta-hydroxylase inhibitor, and was greatest in mitochondria from the adrenal zone having the highest 11 beta-hydroxylase activity. Steroid substrates for 11 beta-hydroxylation inhibited the production of the SL metabolite. Mitochondrial incubations with SL or with 7 alpha-thio-SL in the presence or absence of an NADPH-generating system did not affect cytochrome P-450 concentrations. The results indicate that, unlike the microsomal effects of SL, local activation of SL is not responsible for the destruction of adrenal mitochondrial cytochromes P-450. The major adrenal mitochondrial metabolites of SL appear to be 11 beta-hydroxy-SL and 7 alpha-thio-SL.

A comparison between spironolactone and hydrochlorothiazide with and without alpha-methyldopa in the treatment of hypertension

In a single blind crossover trial, spironolactone (50 mg twice a day), and hydrochlorothiazide (50 mg twice a day) were equally effective hypotensive agents in 16 patients with untreated essential hypertension. The addition of alpha-methyldopa (250 mg three times a day) to each agent produced a further significant and equal fall in blood pressure. Spironolactone therapy was assoicated with fewer clinical and biochemical side effects. The hypotensive effect of the diuretics was independent of the renin status of the patients.

Amiloride in the treatment of primary hyperaldosteronism and essential hypertension

Amiloride (40 mg/day) was given to nineteen patients with primary hyperaldosteronism. There were significant falls in systolic and diastolic blood pressure, in total exchangeable sodium, and in serum sodium sodium and bicarbonate; while total exchangeable potassium, total body potassium, serum potassium, chloride and urea, and plasma renin, angiotensin II and aldosterone all increased significantly. Amiloride was effective in reducing blood pressure in patients with and without adrenocortical adenoma. No carry-over effect was seen on withdrawing amiloride. Similar changes were associated with amiloride treatment in five patients with essential hypertension; hyperkalaemia was not observed. Only negligible side-effects were encountered in the entire series of twenty-four patients.

Effect of high dose spironolactone and chlorthalidone in essential hypertension: relation to plasma renin activity and plasma volume

The effect on blood pressure of high (400 mg/day-S400) and moderate dose (200 mg/day-S200) spironolactone and chlorthalidone (100 mg/day-C100), given in a random double-blind manner was related to plasma renin activity and plasma volume in 38 essential hypertensives. The fall in pressure from a control of 154/103 mm Hg was essentially the same after four weeks of each drug--S400 deltaBP 24/13 mm, S200 18/9 mm, C100 17/12 mm (all P less than 0-001). Twelve of 37 patients (32%) had low initial renin, but this appeared as responsive to the chlorthalidone stimulus as that of the normal renin group. The antihypertensive effect of all regimens was unrelated to plasma renin activity. Plasma volume was significantly lowered at the end of each treatment period, but the decline could not be correlated with blood pressure effects. Patients with initially low plasma volume were more likely to respond to S400 (r = 0-545, P less than 0-001), whereas the antihypertensive effect of the S200 and C100 regimens was independent of this variable.

Rectal potential difference in the diagnosis of aldosterone excess

Rectal potential difference (pd) is directly related to the plasma aldosterone concentration, and rises when aldosterone is stimulated by sodium deprivation. However, when the measurement of rectal pd was tested at a screening test for hyperaldosteronism in 19 hypertensive subjects, four of the eight with primary hyperaldosteronism had a normal pd and four of the eight without aldosterone excess had an abnormally raised potential difference. The technique cannot therefore be recommended as a routine screening test for hyperaldosteronism. No relationship was found between rectal pd and hypertension associated with excess of deoxycorticosterone. Rectal pd rises in response to the mineralocorticoid-like agent carbenoxolone.

Diuretics: mechanism of action and clinical application

Despite the bewildering number of diuretics available to the physician, these drugs can be divided into 4 main groups, characterised by their site of action on sodium reabsorption in the kidney. Drugs acting on the ascending limb of the loop of Henle have a powerful but short acting diuretic effect; they include frusemide, ethacrynic acid and bumetanide. The benzothiadiazines and related compounds have a moderate diuretic action spread over a longer period, whilst the potassium-sparing diuretics, triamterene, amiloride and spironolactone, have only a weak diuretic effect but a marked ability to diminish urinary potassium excretion. The fourth group is made up of miscellaneous substances which function as vasodilator or osmotic agents. The pathogenesis of oedema formation in heart failure is outlined and a logical approach to treatment suggested. Duiretics are being increasingly used in the treatment of non-oedematous states, in particular hypertension, diabetes insipidus and hypercalciuria; their exact role in pregnancy and acute renal failure remains controversial. Side-effects can be related to their effect on electrolyte excretion and include hypokalaemia, hyponatraemia, hyperkalaemia and hyperuricaemia. The incidence of disturbed carbohydrate tolerance in previously normal individuals is low. Other less common side-effects are also discussed.