Assay and properties of 18-hydroxylation of endogenous and exogenous corticosterone in rat adrenals. Evidence for heterogeneity of 18-hydroxylase activity.
(1/19)
A mass fragmentographic technique for assay of 18-hydroxylation of labeled (exogenous) and unlabeled (endogenous) corticosterone in adrenal mitochondria and in reconstituted cytochrome P-450 systems has been developed. An extract of an incubation of [14-14C]corticosterone is subjected both to thin-layer radiochromatography and to mass fragmentography (as O-methyloxime-trimethylsilyl ether derivative). In the latter procedure the ions at m/e 605 and 607 (specific for the derivatives of unlabeled and labeled 18-hydroxycorticosterone, respectively), at m/e 591 and 593 (specific for the derivatives of unlabeled labeled aldosterone, respectively) and at m/e 548 and 550 (specific for the derivatives of unlabeled and labeled corticosterone, respectively) were followed through the gas-liquid chromatography. From the ratio between the peaks obtained in the mass fragmentography and from the percentage conversion of [4-14C]corticosterone obtained in the thin-layer radiochromatography, the amount of endogenous and exogenous 18-hydroxycorticosterone and aldosterone could be calculated. The effects of time, enzyme, and substrate concentration of 18-hydroxylation were studied and optimal conditions for assay were determined. Under most conditions, the ratio between labeled and unlabeled 18-hydroxylated products was about constant, indicating that labeled and unlabeled corticosterone were not in equilibrium. It was ascertained that the 18-hydroxycorticosterone and aldosterone formed in the incubations were derived from corticosterone. [4-14C]18-Hydroxydeoxycorticosterone was not converted into aldosterone or 18-hydroxycorticosterone. In vitro studies with different 18-hydroxylase inhibitors (spironolactone, canrenone, and canrenoate-K) and studies with rats pretreated with KCl in drinking fluid suggest that 18-hydroxylation of corticosterone is catalyzed by an enzyme system different from that catalyzing 18-hydroxylation of deoxycorticosterone. (+info)
Digoxin assays: frequent, substantial, and potentially dangerous interference by spironolactone, canrenone, and other steroids.
(2/19)
BACKGROUND: A case of digoxin toxicity resulted from falsely low values with the MEIA II assay for digoxin (AxSYM; Abbott). The low results were caused by negative interference from canrenone and spironolactone, the latter of which has recently been advocated for the treatment of severe heart failure. Analytical interference from spironolactone has been reported, but little information is available for this effect with newer digoxin assays. METHODS: We examined nine assays (AxSYM, IMx, TDx, Emit, Dimension, aca, TinaQuant, Elecsys, and Vitros for interference by spironolactone, canrenone, and three metabolites. Additionally, all routine digoxin measurements (AxSYM) over a period of 16.5 months (n = 3089) were monitored for interference. RESULTS: Suppression of the expected values by canrenone (3125 microg/L) was observed for the AxSYM (42% of expected value), IMx (51%), and Dimension (78%) assays. A positive bias was observed for the aca (0.7 microg/L), the TDx (0.62 microg/L), and the Elecsys (>0.58 microg/L). Twenty-five of 669 routinely monitored patients had falsely low results. Nineteen of these had potentially toxic concentrations of digoxin (Emit; >2.0 microg/L), although the AxSYM assay indicated therapeutic or less severe toxic concentrations (Delta(max) = 7.1 microg/L). Except for two unresolved cases, this was attributable to spironolactone, canrenone, hydrocortisone, or prednisolone. Standard doses of spironolactone (up to 50 mg/day) in patients with heart failure displayed inhibition <11%. CONCLUSIONS: The frequency and magnitude of the false-negative results particularly compromise the use of both microparticle enzyme immunoassays. Not only may toxic concentrations remain unidentified, but intoxication could occur should dosage be increased because of falsely low results. With 11 million digoxin tests/year ordered in the US, conceivably many patients could be adversely affected. (+info)
Aldosterone antagonist improves diastolic function in essential hypertension.
(3/19)
Experimental studies demonstrated that mineralocorticoid antagonists prevent or reverse myocardial fibrosis. Therefore, we tested the hypothesis that the aldosterone antagonist canrenone can improve left ventricular diastolic function in essential hypertension. Using digitized M-mode echocardiography and 24-hour blood pressure monitoring (ABPM), we realized a prospective, randomized, controlled study on 34 never-treated essential hypertensives with left ventricular diastolic dysfunction. Echocardiogram and ABPM were repeated after 6 months of effective antihypertensive treatment with ACE inhibitors and calcium antagonists (second evaluation) and then after a 6-month period with 17 patients randomly assigned to add canrenone 50 mg/d to the previous treatment (third evaluation). At the basal evaluation 32 patients had left ventricular concentric hypertrophy, and 2 patients had left ventricular concentric remodeling. All the patients had normal left ventricular systolic function. At the second evaluation blood pressure was reduced (P<0.0001), left ventricular mass index decreased (P<0.0001), and diastolic function improved (P<0.0001). After randomization, the canrenone and control groups had similar 24-hour blood pressure and left ventricular morpho-functional characteristics. At the third evaluation, despite unchanged blood pressure and similar decrease of left ventricular mass index, the canrenone group, compared with control group, showed a significantly greater increase in left ventricular diastolic indices. In essential hypertension, a low dose of aldosterone antagonist added to antihypertensive treatment significantly improved left ventricular diastolic function. This improvement, not accounted for by changes in blood pressure and left ventricular mass, can be therefore ascribed to a direct action of the drug on the myocardium. (+info)
Aldosterone receptor blockade improves left ventricular remodeling and increases ventricular fibrillation threshold in experimental heart failure.
(4/19)
OBJECTIVES: To investigate the effects of aldosterone receptor blockade in postinfarction heart failure. METHODS: Eighty-seven rats with moderate myocardial infarction were randomized to receive either no drug or canrenone, the active metabolite of spironolactone, 20 mg/kg/day, or ramipril, 1 mg/kg/day, or a combination of the two drugs. Treatment was initiated 1 month after coronary ligation and lasted 4 weeks. Echocardiography was performed at baseline and after 4 weeks. LV catheterization, isolated heart studies, morphometric histology, myocardial norepinephrine and SERCA-2 mRNA were assessed at the end of the treatment period. RESULTS: Infarct sizes were 33+/-3, 32+/-3, 34+/-3, and 34+/-4% in the placebo, canrenone, ramipril, and combination groups, respectively. Canrenone attenuated LV remodeling, improved LV systolic and diastolic function, and markedly reduced interstitial and perivascular fibrosis. These effects were increased by concomitant ramipril therapy. Moreover, myocardial norepinephrine content was decreased while ventricular fibrillation threshold significantly augmented by canrenone. SERCA-2 levels remained unchanged. CONCLUSIONS: Canrenone attenuated LV dilation and interstitial remodeling, and improved LV filling dynamics and systolic function in the rat model of postinfarction heart failure. Addition of ramipril conferred further cardioprotection. Canrenone also reduced myocardial norepinephrine content and increased ventricular fibrillation threshold. The data provide a potential explanation for the decreased sudden death observed in the RALES study. The mechanisms of action of aldosterone inhibition are still poorly understood, despite its proven efficacy in heart failure. Rats with postinfarction heart failure were randomized to receive for 1 month either no drug or canrenone, or ramipril, or a combination of canrenone and ramipril. Canrenone treatment was associated with a significant attenuation of LV dilation, better LV diastolic and systolic dynamics, and a marked reduction of reactive fibrosis. These effects were enhanced by concomitant ramipril therapy. Moreover, canrenone increased ventricular fibrillation threshold and reduced myocardial norepinephrine content. The data may explain the reduced mortality demonstrated by the RALES. (+info)
Safety of low-dose spironolactone administration in chronic haemodialysis patients.
(5/19)
BACKGROUND: Prevention of cardiovascular diseases is essential in chronic haemodialysis patients. Recently, low-dose spironolactone has been shown to decrease cardiovascular mortality in patients with severe heart failure. However, since haemodialysis patients are prone to hyperkalaemia, a known side effect of spironolactone, this treatment is not used in this population. We performed a study to assess whether low-dose spironolactone (3 x 25 mg/week) could be administered without inducing hyperkalaemia in haemodialysis patients. METHODS: The study design included a 2-week baseline period, followed by a 4-week treatment period in which doses of spironolactone were started at 12.5 mg three times/week for 2 weeks, then increased to 25 mg three times/week, and followed by a 2-week wash-out period. Fourteen patients receiving low-dose spironolactone after each dialysis were compared with 21 haemodialysis patients (control group). RESULTS: Low-dose spironolactone did not change mean serum potassium (4.9 +/- 0.7 vs 4.9 +/- 0.3 mmol/l: control). The mean plasma canrenone level induced by administration of spironolactone 25 mg three times/week in the 14 treated patients was 13 +/- 5.3 ng/ml. Serum aldosterone was not significantly modified by the administration of spironolactone in these patients [before, median 0.35; interquartile range (IQR) 0.11-2.83 nmol/l vs after, median 0.22; IQR 0.12-0.60 nmol/l, NS]. Dietary potassium intake and the use of ion-exchange resin, angiotensin-converting enzyme inhibitors and beta-blockers were similar for the two groups throughout the study. CONCLUSION: This non-randomized and non-blinded study shows that administration of 25 mg spironolactone thrice weekly is not associated with an increased frequency of hyperkalaemia in haemodialysis patients when they are carefully monitored. More studies are required, however, before concluding that spironolactone administration is safe in the chronic haemodialysis population. (+info)
The negative inotropic action of canrenone is mediated by L-type calcium current blockade and reduced intracellular calcium transients.
(6/19)
Spironolactone and canrenone inhibit UGT2B7-catalyzed human liver and kidney microsomal aldosterone 18beta-glucuronidation: a potential drug interaction.
(8/19)