Effect of aldosterone antagonist canrenone on plasma aldosterone concentration and plasma renin activity, and on the excretion of aldosterone and electrolytes by man

Anti-aldosterone therapy in the treatment of heart failure: new thoughts on an old hormone

Activation of the renin-angiotensin-aldosterone system (RAAS) is a prominent feature of left ventricular dysfunction and plays an important role in the progression of chronic heart failure. Clinical and animal studies investigating agents that interrupt this hormonal system have focused primarily on the proximal constituents of the RAAS, namely angiotensin converting enzyme inhibitors and angiotensin II receptor antagonists, and have largely neglected the possible pathological consequences of another hormone in the system, aldosterone. Clinical evidence indicates that aldosterone plays an important role in chronic heart failure, even when other RAAS inhibiting agents are employed. Moreover, animal studies have indicated that aldosterone, in addition to important renal effects, has direct cardiac and vascular effects. These data suggest that an anti-aldosterone therapeutic may provide important protection in chronic heart failure. Currently, only one therapeutic is available, spironolactone (Aldactone), and recent clinical studies support the contention that the addition of spironolactone to standard heart failure therapy provides additional benefit. A highly selective aldosterone receptor antagonist, eplerenone, is currently in clinical development. Data from this new agent should provide important evidence supporting the benefit of anti-aldosterone therapy in chronic heart failure, which may encourage physicians to include an anti-aldosterone agent in the armamentarium of therapeutics currently used to combat chronic heart failure.

Effect of spironolactone on electrolytes, renin, ACTH and corticosteroids in the rat

Spironolactone (S), known to act as a mineralocorticoid antagonist, has been shown in some circumstances to inhibit steroid biosynthesis. To investigate these two actions in vivo in the rat, animals fed a normal or low Na+ diet were treated with S for 7 days. In animals fed a normal Na+ diet, urinary and faecal electrolytes, aldosterone and corticosterone excretion were measured daily, plasma renin, aldosterone, corticosterone, ACTH, progesterone, DOC and 18-OH-DOC were determined after 4 and 7 days of treatment. In animals fed a low Na+ diet, urinary electrolytes were measured daily and plasma and urinary aldosterone and corticosterone were determined at intervals during the introduction of the diet and in the course of treatment. On a normal Na+ diet, S induced a slight non significant rise in the urinary Na+/K+ ratio on the first day of treatment, no change in faecal electrolyte excretion, and a sustained increase in aldosterone but not in corticosterone excretion. It produced a 6-fold elevation in plasma aldosterone levels, a less marked rise in renin and progesterone, a delayed increase in DOC and no change in ACTH, 18-OH-DOC or corticosterone concentration. On a low Na+ diet, treatment induced a rise in the urinary Na+/K+ ratio, and in urine and plasma aldosterone levels and no change in corticosterone values. Our results confirm, in the intact rat, the antimineralocorticoid action of S characterized by an increase in Na+ excretion but no change in K+ elimination. No inhibitory effect of spironolactone on aldosterone, corticosterone or 18-OH-DOC biosynthesis could be demonstrated in our experimental model.

Distal tubular segments of the rabbit kidney after adaptation to altered Na- and K-intake. I. Structural changes

The baso-lateral cell-membrane area in kidney tubules appears to be associated with the capacity for electrolyte transport; in the rabbit, it decreases from the distal convoluted tubule (DCT-cells) over the connecting tubule (CNT-cells) to the cortical collecting duct (principal cells). Adaptation to low Na-, high K-intake changes this pattern: CNT-cells at the beginning of the connecting tubule have the highest membrane area, which decreases along the segment, but remains two-fold higher than in controls. Principal cells have a four-fold higher membrane area than in controls. Simultaneous treatment with the antimineralocorticoid canrenoate-K inhibits the structural changes in CNT-cells only in end-portions of the connecting tubule and in principal cells. After prolonged high Na-, low K-intake DCT-cells display a two-fold higher membrane area than controls, while CNT-cells and principal cells are not affected. Simultaneous treatment with DOCA does not affect the DCT-cells but provokes a moderate increase in membrane area in CNT-cells, and a 5.5-fold increase in principal cells. The data provide evidence that DCT-, CNT- and principal cells are functionally different cell types. The baso-lateral cell-membrane area, associated with electrolyte-transport capacity, appears to be influenced in DCT-cells mainly by Na-intake, in CNT-cells mainly by K-intake and in part also by mineralocorticoids, and in principal cells mainly by mineralocorticoids.

A comparison of some extra-renal effects of spironolactone and canrenone

1 Measurement of changes in trans-mural rectal potential difference (t.m.r.p.d.) and plasma aldosterone levels have been used in a comparison of the extra-renal activities of spironolactone and its major metabolite canrenone. 2 A characteristic pressure artifact was observed during measurement of t.m.r.p.d. When pressure artifacts were eliminated, there was a log-linear relationship between increasing doses of intravenous aldosterone and maximum increase in t.m.r.p.d. 3 Pre-treatment for 5 days with spironolactone or canrenone produced a similar attenuation of the increase in t.m.r.p.d. produced by infused aldosterone, suggesting that canrenone is the active metabolite of spironolactone in the rectum. This is in contrast to the significantly greater renal activity of spironolactone that has been demonstrated after a similar treatment period. Neither antagonist treatment produced significant changes in pre-infusion plasma aldosterone concentrations. 4 The need for assay of the extra-renal activities of aldosterone antagonists in the assessment of their therapeutic potential is discussed.