Interactions of enhanced urocortin 2 and mineralocorticoid receptor antagonism in experimental heart failure.

BACKGROUND: Mineralocorticoid receptor antagonists (MRAs) have become established therapy in heart failure (HF). Urocortin 2 (Ucn2) is a novel peptide with potential in the treatment of this disease. The present study investigated the interactions of acute administration of Ucn2 and an MRA in experimental HF. METHODS AND RESULTS: Ucn2 and an MRA (canrenoic acid [CA]) were infused for 4 hours, both singly and together, in 8 sheeps with pacing-induced HF. Ucn2, when administered as an adjunct to CA, further improved hemodynamic indices relative to that achieved by CA alone, producing additional increases in cardiac output and decreases in left atrial pressure and peripheral resistance but without eliciting a supplementary reduction in arterial pressure. Ucn2 cotreatment reversed CA-induced rises in circulating aldosterone levels, and also significantly reduced plasma renin activity, angiotensin II, and vasopressin concentrations. Although both CA and Ucn2 infusion produced a diuresis and natriuresis, responses with Ucn2 and Ucn+CA were 2- to 3-fold greater than that elicited by separate CA. Ucn2 cotherapy additionally increased urine potassium and creatinine excretion. In contrast to the rise in plasma potassium induced by CA, Ucn2 cotreatment reduced potassium concentrations. CONCLUSIONS: Ucn2 cotreatment with an MRA in HF further improved hemodynamics relative to that achieved by CA alone, while also reducing plasma renin activity, angiotensin II, aldosterone and vasopressin levels, and enhancing renal function. Importantly, Ucn2 prevented CA-induced rises in plasma potassium. These data demonstrate a favorable profile of effects with short-term adjunct Ucn2 therapy and an MRA in HF.

Effect of spironolactone, potassium canrenoate, and their common metabolite canrenone on Dimension Vista Digoxin Assay.

Spironolactone, a potassium sparing diuretic metabolized to canrenone, is often used with digoxin to treat various conditions including congestive heart failure. Potassium canrenoate is a similar drug that is also metabolized to canrenone. Due to reported interference of spironolactone, potassium canrenoate, and their common metabolite canrenone with digoxin immunoassays, we investigated potential interference of these compounds with Dimension Vista Digoxin immunoassay using Flex reagent cartridge. Aliquots of a drug-free serum pool were supplemented with various amounts of spironolactone, potassium canrenoate, or canrenone and apparent digoxin values were measured using Dimension Vista digoxin assay, we observed none-detected value except when aliquots were supplemented with higher amounts of spironolactone or canrenone. Similarly, when aliquots of a serum digoxin pool (prepared by pooling specimens from patients receiving digoxin) where further supplemented with various amounts of spironolactone, potassium canrenoate, or canrenone, we observed moderately falsely elevated digoxin values only in specimens containing higher amounts of spironolactone or canrenone. We conclude that spironolactone and canrenone but not potassium canrenoate may cause modest interference with Dimension Vista digoxin assay but such interferences may not be clinically significant except with very high amounts of canrenone.

Effect of acute and prolonged mineralocorticoid receptor blockade on spontaneous and stimulated hypothalamic-pituitary-adrenal axis in humans.

CONTEXT: Mineralocorticoid receptors (MRs) in the hippocampus display an important role in the control of the hypothalamic-pituitary-adrenal (HPA) axis, mediating the proactive feedback of glucocorticoids, which maintains the basal HPA activity. The systemic administration of MR antagonists enhances spontaneous and CRH-stimulated ACTH, cortisol, and DHEA secretion, while the effects of chronic treatment with MR antagonists are scanty. Our study was performed in order to clarify this point. DESIGN: ACTH, cortisol, and DHEA levels were studied during the infusion of placebo, canrenoate, a MR antagonist (CAN, 200 mg i.v. bolus at 1600 h followed by 200 mg infused over 4 h), and human CRH (hCRH; 2.0 microg/kg i.v. bolus at 1800 h) before and during the last week of 28-day treatment with CAN (200 mg/day p.o.) in eight young women. RESULTS: Pre-treatment sessions: CAN and hCRH administration increased ACTH, cortisol, and DHEA levels versus placebo (P<0.05). Post-treatment sessions: during placebo infusion, cortisol and DHEA were significantly amplified versus pre-treatment session (P<0.05), while ACTH levels were not modified; CAN infusion, differently from pre-treatment session, was not able to significantly increase ACTH, cortisol, and DHEA levels; ACTH, cortisol, and DHEA responses to hCRH were amplified with respect to pre-treatment session, although statistical significance was obtained for cortisol and DHEA only. CONCLUSIONS: MR blockade by acute CAN administration significantly enhances the HPA activity in the afternoon, during the quiescent phase of the circadian rhythm. At the same period, prolonged treatment with CAN amplifies both spontaneous and CRH-stimulated activities of the HPA axis, while it blunts the HPA responsiveness to a further MR-mediated stimulation.

Fadrozole reverses cardiac fibrosis in spontaneously hypertensive heart failure rats: discordant enantioselectivity versus reduction of plasma aldosterone.

Reversal of cardiac fibrosis is a major determinant of the salutary effects of mineralocorticoid receptor antagonists in heart failure. Recently, R-fadrozole was coined as an aldosterone biosynthesis inhibitor, offering an appealing alternative to mineralocorticoid receptor antagonists to block aldosterone action. The present study aimed to evaluate the effects of R- and S-fadrozole on plasma aldosterone and urinary aldosterone excretion rate and to compare their effectiveness vs. the mineralocorticoid receptor antagonist potassium canrenoate to reverse established cardiac fibrosis. Male lean spontaneously hypertensive heart failure (SHHF) rats (40 wk) were treated for 8 wk by sc infusions of low (0.24 mg/kg.d) or high (1.2 mg/kg.d) doses of R- or S-fadrozole or by potassium canrenoate via drinking water (7.5 mg/kg.d). At the high dose, plasma aldosterone levels were decreased similarly by R- and S-fadrozole, whereas urinary aldosterone excretion rate was reduced only by S-fadrozole. In contrast, whereas at the high dose, R-fadrozole effectively reversed preexistent left ventricular interstitial fibrosis by 50% (vs. 42% for canrenoate), S-fadrozole was devoid of an antifibrotic effect. The low doses of the fadrozole enantiomers did not change cardiac fibrosis or plasma aldosterone but similarly reduced urinary aldosterone excretion rate. In conclusion, R-fadrozole may possess considerable therapeutic merit because of its potent antifibrotic actions in the heart. However, the observed discordance between the aldosterone-lowering and antifibrotic effects of the fadrozole enantiomers raises some doubt about the mechanism by which R-fadrozole diminishes cardiac collagen and about the generality of the concept of lowering aldosterone levels to treat the diseased heart.

Electropharmacological effects of a spironolactone derivative, potassium canrenoate, assessed in the halothane-anesthetized canine model.

While aldosterone receptor blockers improve survival of patients with congestive heart failure, spironolactone and its derivatives were recently shown to block ether-a-go-go-related gene (HERG) channels and native IKs and IKr currents in guinea pig ventricular myocytes. In this study, we examined in vivo electropharmacological effects of an active derivative of spironolactone, potassium canrenoate, using a halothane-anesthetized canine model. Potassium canrenoate was intravenously administered in three doses of 1, 10, and 100 mg/kg per 10 min with a pause of 20 min between doses (n = 5). The low dose hardly affected any of the cardiovascular parameters. The middle dose, a clinically recommended daily maximum i.v. dose, slightly inhibited the intraventricular conduction. The high dose decreased the heart rate, ventricular contraction and blood pressure, delayed the atrioventricular and intraventricular conduction, and prolonged the ventricular repolarization and refractory period. Increment in the refractoriness by the high dose was greater than that in the repolarization, resulting in the reduction of ventricular electrical vulnerability. This unique electrophysiological profile of potassium canrenoate may in part contribute to the favorable clinical results, whereas caution has to be paid on the cardiohemodynamic actions, particularly for patients with risk of elevated plasma drug concentration.

The stimulatory effect of canrenoate, a mineralocorticoid antagonist, on the activity of the hypothalamus-pituitary-adrenal axis is abolished by alprazolam, a benzodiazepine, in humans.

Mineralocorticoid receptors (MR) in the hippocampus play a major role in the control of the hypothalamus-pituitary-adrenal (HPA) axis, mediating the proactive feedback of glucocorticoids in the maintenance of basal activity. Intracerebroventricular and intrahippocampal MR blockade stimulates HPA axis in animals; the systemic administration of mineralocorticoid antagonists enhances spontaneous and CRH-stimulated ACTH and cortisol secretion in humans. Benzodiazepines, namely alprazolam, activate central gamma-aminobutyric acid (GABA)ergic receptors, which are mainly distributed in the hippocampus. Alprazolam has a inhibitory effect on HPA axis either in basal conditions or after central nervous system-mediated stimuli. In humans, alprazolam strongly reduces the corticotroph responsiveness to removal of glucocorticoid feedback by metyrapone. We studied the effect of alprazolam (0.02 mg/kg, orally) on the effect of canrenoate (CAN), an MR antagonist (200 mg as an iv bolus, followed by 200 mg infused in 250 ml saline) or placebo on ACTH, cortisol, and dehydroepiandrosterone (DHEA) secretion in six normal young women (aged 25-32 yr; body mass index, 19-23 kg/m(2)). During placebo, ACTH, cortisol, and DHEA secretion showed a progressive decrease (baseline vs. nadir, mean +/- SEM, from 1830-2400 h, 2.6 +/- 0.3 vs. 1.4 +/- 0.3 pmol/liter, 133.2 +/- 16.4 vs. 46.9 +/- 5.2 nmol/liter, and 22.6 +/- 2.3 vs. 18.6 +/- 2.3 nmol/liter, respectively), although statistical significance was obtained for ACTH and cortisol only (P < 0.05). During CAN treatment, ACTH, cortisol, and DHEA secretion showed a progressive rise, which began at approximately 2100 h and peaked between 2300 and 2400 h (2.9 +/- 0.3 pmol/liter, 172.6 +/- 27.9 nmol/liter, and 45.3 +/- 10.7 nmol/liter, respectively; P < 0.05). Alprazolam abolished the CAN-induced increases in ACTH, cortisol, and DHEA levels (1.8 +/- 0.1 pmol/liter, 59.7 +/- 8.6 nmol/liter, and 19.8 +/- 6.7 nmol/liter; P < 0.05), inducing hormonal peaks overlapping with those recorded after placebo in the absence of any treatment. In conclusion, our study demonstrates that the inhibitory effect of GABAergic activation by alprazolam overrides the stimulatory effect of mineralocorticoid blockade by canrenoate on the HPA axis in humans. These findings emphasize the role of GABA in the control of the HPA axis in humans.

Bidirectional (positive/negative) interference of spironolactone, canrenone, and potassium canrenoate on serum digoxin measurement: elimination of interference by measuring free digoxin or using a chemiluminescent assay for digoxin.

Spironolactone and potassium canrenoate (aldosterone antagonist diuretics) are often used with digoxin in clinical practice. Spironolactone, potassium canrenoate, and their common metabolite canrenone cross-react with the fluorescence polarization immunoassay (FPIA) for digoxin, and can falsely elevate serum digoxin concentrations. Serum digoxin concentrations were falsely lowered when the microparticle enzyme immunoassay (MEIA) was used. Aliquots of drug-free serum were supplemented with therapeutic and above-therapeutic concentrations of spironolactone, canrenone, and potassium canrenoate, and apparent digoxin activities were measured. We observed digoxin-like activities in the FPIA, but observed no activity with the MEIA or the chemiluminescent assay (CLIA). However, when serum digoxin pools prepared from patients receiving digoxin were supplemented with these compounds, we observed suppression of total digoxin levels with the MEIA. In contrast, no interference was observed in the presence of these compounds when CLIA was used for digoxin measurement. These compounds are strongly protein-bound, and no apparent digoxin activity was observed in the protein-free ultrafiltrate when drug-free sera were spiked with high levels of these compounds. Taking advantage of strong protein binding of these compounds and weak protein binding of digoxin (25%), interference of spironolactone, canrenone, and potassium canrenoate in FPIA and MEIA digoxin assays can be mostly eliminated by monitoring free digoxin concentration. Another approach to avoid this interference is to use the CLIA digoxin assay.

Effects of acute mineralocorticoid and glucocorticoid receptor blockade on the excretion of an acute potassium load in healthy humans.

To examine the role of mineralocorticoid and glucocorticoid in potassium (K) tolerance in healthy humans, we studied the effects of canrenoate, a mineralocorticoid antagonist, and RU486, a glucocorticoid antagonist, on the excretion of a KCl load. Canrenoate (200 mg, iv) or RU486 (400 mg, orally) was administered 150 min before a KCl load (1 mmol/kg BW, orally) in seven healthy males undergoing maximal water diuresis. Clearance studies were extended for 5 h after the KCl load, and the data were compared with time control, KCl load alone, and canrenoate alone. KCl increased K excretion (from 18.8 +/- 2.4 to 63.3 +/- 3.9 mmol/5 h; P < 0.01) and sodium (Na) excretion (from 35.9 +/- 2.1 to 72.9 +/- 6.0 mmol/5 h; P < 0.01). Clearance calculations, based on maximal water diuresis, were compatible with increased distal Na and volume delivery. Canrenoate alone modestly increased basal cumulative NaCl excretion and had no effect on K excretion. However, canrenoate blunted the kaliuresis after the KCl load (51.9 +/- 4.4 mmol/5 h; P < 0.05 compared to KCl alone) and stimulated natriuresis in a complementary way. Clearance data were compatible with diminished distal Na reabsorption and K secretion in response to an undisturbed KCl-induced increase in distal Na delivery. RU486 did not influence the excretion of the KCl load or its effects on renal sodium handling parameters, although effective glucocorticoid receptor blockade was likely to be present in view of the increase in plasma cortisol. These data suggest that in healthy humans, mineralocorticoid activity, but not glucocorticoid activity, is involved in the elimination of a K load. The latter contrasts with data in adrenalectomized animals, in which situation glucocorticoid as well as aldosterone are indispensible for normal K tolerance.

Acute effect of potassium canrenoate administration on renin-angiotensin, kallikrein-kinin and prostaglandin systems.

1. To investigate the possible effects of potassium canrenoate (PC) on plasma renin activity (PRA) and on renal prostaglandins (PGS) and kinins under elevated sodium and/or potassium intakes, a single dose of PC was administered to four groups of Wistar male rats. 2. They were fed a normal diet (C), a diet supplemented with 4% of NaCl, (Na), with 1% of KCl: (K) or both supplements (NaK). 3. PRA and urinary PGS excretion did not show changes after PC administration, but total urinary kinins showed higher values after the treatment in all groups. 4. A diuretic but not natriuretic effect was observed only in C animals. 5. In conclusion, the single dose of PC was able to stimulate urinary kinins and to spare potassium independently of dietary electrolyte supplements that were able to block the diuretic effect of the drug.

Progestogens with antimineralocorticoid activity.

The ability of 11 steroids with varying degrees of progestogenic potency to inhibit the renal actions of aldosterone was tested in adrenalectomized, glucocorticoid-treated rats. The rats were continuously infused with an isotonic solution of low sodium content (0.05% NaCl + 5.2% glucose, 3 ml/rat/h) supplemented with d-aldosterone [1 microgram/(kg X h)] resulting in a long-lasting reduction in renal sodium excretion, increase in renal potassium excretion and hence decrease in the urinary Na/K-ratio. The test drugs were administered either subcutaneously or orally 1 h before start of infusion. Their antimineralocorticoid activity was judged by the increase in the aldosterone-lowered Na/K-ratio in urine which was collected at hourly intervals for 15 or 21 h, respectively. Adrenalectomized, glucocorticoid-treated rats receiving an i.v. infusion without aldosterone were used for assessing possible mineralocorticoid effects of the steroids tested. D-Norgestrel, norethisterone acetate, 3-keto-desogestrel (the active metabolite of desogestrel) and cyproterone acetate, respectively, did neither show antimineralocorticoid nor mineralocorticoid activity when injected subcutaneously at a dose of 53.3 mg/kg. In contrast, gestodene (26.7 or 53.3 mg/kg s.c., respectively), progesterone (53.3 mg/kg s.c.), spironolactone (26.7 mg/kg s.c.), spirorenone (13.3 mg/kg s.c.), 1,2-dihydro-spirorenone (13.3 mg/kg s.c.), or 1,2 alpha-methylene-spirorenone (13.3 mg/kg s.c.) exhibited significant anti-mineralocorticoid activity. Canrenone (53.3 mg/kg s.c.) slightly increased the urinary Na/K-ratio. This effect, however, was not significant. Gestodene, like spironolactone or progesterone, was devoid of aldosterone-like mineralocorticoid activity. With the exception of progesterone, the antimineralocorticoid activity of the steroids tested could also be demonstrated after oral administration. Based on the Na/K-ratio or the log (Na X 100)/K-ratio, the potency of each test compound relative to spironolactone was evaluated using regression analysis. The following results (average relative potency, spironolactone = 1.0) were obtained: gestodene: approximately 0.2; canrenone: approximately 0.3-0.35; spirorenone: approximately 7-8; 1,2-dihydro-spirorenone: approximately 8; 1,2 alpha-methylene-spirorenone: approximately 3.5. Progesterone which was evaluated after s.c. injection exhibited an average relative potency of approximately 0.35. Due to these results, gestodene may be regarded as the first progestogen of the nortestosterone series exhibiting a more natural, progesterone-like profile of activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Sheep renal potassium excretion: efferent kaliuretic regulatory factors.

The possibility that efferent factors in addition to aldosterone and plasma K may mediate the renal response to large variations in K intake in sheep was explored in experiments on four mature ewes. K supplementation of a normal diet provided a total K intake of 1,300-1,500 meq/day for 3 days and produced a high K excretion (737 +/- 34 mu eq/min) with plasma K 4.67 +/- 0.07 meq/liter. K deprivation by 83 h of fasting produced low K excretion (48 +/- 10 mu eq/min) with plasma K 3.60 +/- 0.14 meq/liter. Additional treatments during both K-supplemented and K-deprived states included: raising plasma K through the range 4-7 meq/liter by intravenous infusion of 45 meq KCl in 30 min; intravenous infusion of aldosterone (20 micrograms/h) or of an aldosterone antagonist, potassium canrenoate (100 mg/h). Na supplementation during fasting was by rumen infusion of Na acetate-Na propionate (1,000 meq Na/day). Results showed that the increase in plasma K during intravenous K infusion directly elevated K excretion, that aldosterone enhanced and canrenoate depressed the kaliuretic effect of K infusion, and that Na loading during fasting enhanced the kaliuretic effect of aldosterone. Comparisons, made at the same level of plasma K, indicated that differences in plasma K, aldosterone, or Na excretion were not sufficient individually or in combination to account for the large differences of 350-1,150 mu eq/min in K excretion that existed between K-supplemented and K-deprived states. Unidentified kaliuretic regulatory factors appear to play a major role in the homeostatic control of K excretion in sheep under the circumstances of these experiments.