[Role of cardiac aldosterone in post-infarction ventricular remodeling in rats]. / Rôle de l'aldostérone cardiaque dans le remodelage ventriculaire du postinfarctus chez le rat.

Synthesis of aldosterone (Aldo) and corticosterone (B) has been recently reported in rat heart. However, regulation of this synthesis in pathophysiological states remains unknown. Thus, this study aimed to analyze effects of a one-month myocardial infarction (MI) on cardiac steroidogenic system. Levels of terminal enzymes of B (11 beta-hydroxylase: 11 beta H) and aldo (Aldo-synthase: AS) synthesis were assayed by quantitative RT-PCR. Cardiac Aldo and B levels were assessed by celite colum chromatography and radioimmunoassay. MI raised AS mRNA levels by 2.0-fold (p < 0.05) but downregulated that of 11 beta H by 2.4 fold (p < 0.05) in the noninfarcted part of the left ventricle (LV). Cardiac steroids production followed a similar pattern of regulation. Aldo level was increased in MI (319 +/- 85 vs 87 +/- 11 pg/mg of protein in control, p < 0.05) whereas that of B fell (2,412 +/- 318 vs 4,624 +/- 857 pg/mg of protein in control, p < 0.05). MI also induced an 1.9-fold increase in cardiac Ang II level. Such cardiac regulations were prevented by Ang II-AT1 receptor antagonist losartan (8 mg/kg/day) treatment. The Aldo receptor antagonist spironolactone (20 mg/kg/day) had no effect. Plasma Aldo and B, and adrenal 11 beta H and AS mRNA levels were unchanged whatever the treatment. The MI-induced collagen deposition in noninfarcted area of the LV was reduced by both spironolactone and losartan treatments by 1.6- and 2.5-fold, respectively. These data indicate that MI is associated with tissue-specific activation of myocardial aldosterone synthesis. This activation is mediated by cardiac Ang II via AT1 receptor and the resultant increase of intracardiac aldosterone level may be involved in post-MI ventricular remodeling.

Activation of cardiac aldosterone production in rat myocardial infarction: effect of angiotensin II receptor blockade and role in cardiac fibrosis.

BACKGROUND: This study analyzed the regulation and the role of the cardiac steroidogenic system in myocardial infarction (MI). METHODS AND RESULTS: Seven days after MI, rats were randomized to untreated infarcted group or spironolactone- (20 and 80 mg x kg-1 x d-1), losartan- (8 mg x kg-1 x d-1), spironolactone plus losartan-, and L-NAME- (5 mg x kg-1 x d-1) treated infarcted groups for 25 days. Sham-operated rats served as controls. In the noninfarcted myocardium of the left ventricle (LV), MI raised aldosterone synthase mRNA (the terminal enzyme of aldosterone synthesis) by 2. 0-fold and the aldosterone level by 3.7-fold. Conversely, MI decreased 11beta-hydroxylase mRNA (the terminal enzyme of corticosterone synthesis) by 2.4-fold and the corticosterone level by 1.9-fold. MI also induced a 1.9-fold increase in cardiac angiotensin II level. Such cardiac regulations were completely prevented by treatment of the infarcted heart with losartan. The MI-induced collagen deposition in noninfarcted LV myocardium was prevented by 1.6-fold by both low and high doses of spironolactone and by 2.5-fold by losartan. In addition, norepinephrine level was unchanged in infarcted heart but was attenuated by both losartan and spironolactone treatments. CONCLUSIONS: MI is associated with tissue-specific activation of myocardial aldosterone synthesis. This increase is mediated primarily by cardiac angiotensin II via AT1-subtype receptor and may be involved in post-MI ventricular fibrosis and in control of tissue norepinephrine concentration.

Recombinant CYP11B genes encode enzymes that can catalyze conversion of 11-deoxycortisol to cortisol, 18-hydroxycortisol, and 18-oxocortisol.

CYP11B1 (11beta-hydroxylase) and CYP11B2 (aldosterone synthase) are 93% identical mitochondrial enzymes that both catalyze 11beta-hydroxylation of steroid hormones. CYP11B2 has the additional 18-hydroxylase and 18-oxidase activities required for conversion of 11-deoxycorticosterone to aldosterone. These two additional C18 conversions can be catalyzed by CYP11B1 if serine-288 and valine-320 are replaced by the corresponding CYP11B2 residues, glycine and alanine. Here we show that such a hybrid enzyme also catalyzes conversion of 11-deoxycortisol to cortisol, 18-hydroxycortisol, and 18-oxocortisol. These latter two steroids are present at elevated levels in individuals with glucocorticoid suppressible hyperaldosteronism (GSH) and some forms of primary aldosteronism. Their production by the recombinant CYP11B enzyme is enhanced by substitution of further amino acids encoded in exons 4, 5, and 6 of CYP11B2. A converted CYP11B1 gene, containing these exons from CYP11B2, would be regulated like CYP11B1, yet encode an enzyme with the activities of CYP11B2, thus causing GSH or essential hypertension. In a sample of 103 low renin hypertensive patients, 218 patients with primary aldosteronism, and 90 normotensive individuals, we found a high level of conversion of CYP11B genes and four cases of GSH caused by unequal crossing over but no gene conversions of the type expected to cause GSH.

Isolated aldosterone synthase deficiency caused by simultaneous E198D and V386A mutations in the CYP11B2 gene.

Isolated deficiencies in aldosterone biosynthesis are caused by mutations in the CYP11B2 (aldosterone synthase) gene. Patients with this deficiency have impaired aldosterone synthesis, exhibit increased plasma renin activity, secrete increased amounts of the steroid precursors DOC, corticosterone, and 18OHDOC, and are subject to salt wasting and poor growth. Two forms are generally distinguished. The first, corticosterone methyloxidase type I (CMO I or type 1 deficiency), is characterized by no detectable aldosterone secretion, a low or normal secretion of the steroid 18OHB, and are always found to have mutations that completely inactivate the encoded CYP11B2 enzyme. The second form (CMO II or type 2 deficiency) may have low to normal levels of aldosterone, but at the expense of greatly increased secretion of its immediate precursor 18OHB. These patients usually have a CYP11B2 enzyme with some residual enzymatic activity, especially 11beta-hydroxylase activity. We have studied two twins with an isolated aldosterone synthase activity who have a clinical profile typical of the type 1 deficiency. Their CYP11B2 genes are homozygous for three sequence changes, R173K, E198D, and V386A. In transfection assays these substitutions individually have modest effects on the encoded enzyme, but when found together they result in an enzyme with a decreased 11beta-hydroxylase activity, a large decrease of 18-hydroxylase activity, and no detectable 18-oxidase activity. This residual activity is more typical of that observed in patients classified as having CMO II deficiency, rather than CMO I deficiency, where no activity is detectable. This disparity between the CYP11B2 enzyme with residual activity and a clinical phenotypic typical of the type 1 deficiency, suggests that phenotype genotype relationships are not yet fully understood.

[Primary hyperaldosteronism and adenoma of the adrenal cortex. Suppression of aldosterone with dexamethasone]. / Hyperaldostéronisme primaire par adénome de la glomérulée. Freinage de l'aldostérone par la Dexaméthasone.

The aim of the study was to evaluate dexamethazone test in a patient with primary aldosteronism caused by an adrenocortical adenoma. We observed a 50% decrease of plasma aldosterone as in glucocorticoid suppressible aldosteronism (GSA) but absolute value of aldosterone remained higher than 40 pg/ml. Basal plasma and urinary values of 18 OXO and 18 OH cortisol were not significantly elevated as in GSA. Inversely, the evaluation of 11 beta-hydroxylase activity of mineralocorticoids was in favor of a benign adrenal tumor.

Myocardial production of aldosterone and corticosterone in the rat. Physiological regulation.

Increasing evidence suggests that mineralo- and glucocorticoids modulate cardiovascular homeostasis via the effects of circulating components generated within the adrenals but also through local synthesis. The aim of this study was to assess the existence of such a steroidogenic system in heart. Using the quantitative reverse transcriptase-polymerase chain reaction, the terminal enzymes of corticosterone and aldosterone synthesis (11beta-hydroxylase and aldosterone synthase, respectively) were detected in the rat heart. This pathway was shown to be physiologically active, since production of aldosterone, corticosterone, and their precursor, deoxycorticosterone, was detected in both the homogenate and perfusate of isolated rat hearts using radioimmunoassay after Celite column chromatography. Perfusion of angiotensin II or adrenocorticotropin for 3 h increased aldosterone and corticosterone production and decreased deoxycorticosterone, suggesting that aldosterone and corticosterone are formed within the isolated heart from a locally present substrate. Chronic regulation of this intracardiac system was then examined. As in adrenals cardiac 11beta-hydroxylase and aldosterone-synthase mRNAs were independently regulated by 1 week's treatment with either low sodium and high potassium diet (which increased aldosterone synthase mRNA level only), angiotensin II (which raised level of both mRNAs), or adrenocorticotropin (which stimulated the 11beta-hydroxylase gene exclusively). Changes in cardiac steroid levels during treatment were not directly related to their plasma levels suggesting independent regulating mechanisms. This study, therefore, provides the first evidence for the existence of an endocrine cardiac steroidogenic system in rat heart and emphasizes its potential physiological and pathological relevance.

The amino acid substitutions Ser288Gly and Val320Ala convert the cortisol producing enzyme, CYP11B1, into an aldosterone producing enzyme.

Transfection studies with cDNAs encoding hybrids between the highly similar cytochrome P450 enzymes, CYP11B1 (steroid 11 beta-hydroxylase) and CYP11B2 (aldosterone synthase) have identified which amino acids determine the different activities of the enzymes.

[Aldosterone precursors and hypertension with hypokalemia and adrenal module non caused by primary hyperaldosteronism]. / Précurseurs de l'aldostérone et hypertension artérielle avec hypokaliémie et nodule surrénalien, non attribuée à un hyperaldostéronisme primaire.

The purpose of the study was to evaluate the interest of aldosterone precursors assays in arterial hypertension with hypokaliemia and adrenal nodules non due to aldosterone. Seven hypertensive patients, 3 men and 4 women, aged 59.5 +/- 10.1 years were included in the study. After drug withdrawal, kaliemia was 3.1 +/- 0.3 mmol/l (2.7-3.6), active renin 2.9 +/- 1.4 ng/l, plasma aldosterone (aldo) 108 +/- 49.4 pg/ml, cortisol 13 +/- 3.1 micrograms/100 ml, and [S] 0.47 +/- 0.5 micrograms/100 ml. Adrenal CT scan showed an adenoma in 3 patients (30.5 +/- 5 mm) and an unilateral nodular hyperplasia in 4 patients. In all patients, the plasma levels (RIA, chomatographic step) of the following steroids in the mineralocorticoid (MC) pathway were determined: DOC, 18 OH-DOC, B, 18 OH-B and aldosterone. Two from 7 (28%) exerted aldosterone precursors excess, 1 with DOC-producing adenoma (DOC-PA) (table), and 1 with a partial 11 beta hydroxylase deficiency (DOC: 211 pg/ml; S: 1 mu/100 ml). Aldosterone/DOC + 18 OH-DOC ratio proposed as a malignancy index was decreased in the patient with DOC-PA (8.1). No dysfunction in the MC pathway was identified in the 5 other patients. [table: see text] The study suggests the relevance of aldosterone precursors assays in low renin hypertension non due to aldosterone and in incidentally discovered adrenal masses.

[Dysfunction of the aldosterone synthesis pathway as a marker of malignity in symptomatic and asymptomatic adrenal masses]. / Du dysfonctionnement de la voie de synthèse de l'aldostérone comme marqueur de malignité des masses surrénaliennes symptomatiques et asymptomatiques.

Fundamental research performed in the author's laboratory led to the understanding of mechanisms of the mineralocorticoid biosynthetic pathway. Sensitive assays were then developed to allow measurement of the different mineralocorticoid metabolites in several biological fluids. Using these methods biological markers that contribute to the differential diagnosis between benign and malignant adrenal tumors were identified. In the present paper we report that the exploration of the entire mineralocorticoid pathway in the plasma of patients during basal state and after stimulation and/or inhibition test is a powerful tool to predict or validate diagnosis of adrenal malignancy. Moreover, mineralocorticoid exploration can help differentiate between two different types of malignancy, ie malignant cortical adrenaloma and metastases of other cancer. The biochemical mechanisms leading to the atypical mineralocorticoid metabolism in the case of malignant cortical adrenaloma are now under study.

Plasma levels of aldosterone versus aldosterone precursors: a way to estimate the malignancy of asymptomatic and nonsecretory adrenal tumors: a French Retrospective Multicentric Study.

The aim of this study was to find out whether the dysfunction of aldosterone pathway, previously proposed as a marker of secretory adrenal carcinoma, is also found in nonsecretory adrenal carcinomas, which pose even more difficult diagnostic problems even for patients with hypertension accompanied or not by hypokalemia. The exploration consisted of using the same method (RIA preceded by a chromatographic step) to determine the plasma levels of the following steroids in the mineral corticosteroid pathway: deoxycorticosterone (DOC), 18-hydroxydeoxycorticosterone (18-OHDOC), corticosterone (B), 18 hydroxycorticosterone (18 OH B), and aldosterone. The subjects included 16 adults, each presenting with an endocrinologically asymptomatic adrenal mass associated for some patients with hypokalemia and hypertension (8 with adrenal carcinoma, 2 with adrenal metastasis from other forms of cancer, and 6 adenomas). These results show that even in nonsecretory adrenal carcinoma, there is a dysfunction of the aldosterone pathway, which can be evaluated from the ratio between aldosterone and the substrate of 11 beta hydroxylase (DOC) and its derivative (18-OH DOC). This study suggests that exploration of mineralocorticosteroid pathway can be used as a hormonal marker of adrenal carcinoma for both secretory and non-secretory malignant masses.

[Hyperaldosteronism sensitive to dexamethasone with adrenal adenoma. Clinical, biological and genetic study]. / Hyperaldostéronisme sensible à la dexaméthasone avec adénome surrénalien. Etude clinique, biologique et génétique.

OBJECTIVES: Dexamethasone-sensitive hyperaldosteronism is associated with early onset hypertension and primary hyperaldosteronism. Diagnosis is difficult but can be improved by genetic testing for the mutant gene. METHODS: We collected the clinical, biological and genetic elements observed in a family with dexamethasone-sensible hyperaldosteronism. Complete data were obtained in 5 adult subjects with the disease. Degree of hypertension varied, more so in the second generations as did hypokaliaemia and hyperaldosteronism. In affected patients, there was a 10 to 50 fold increase in urinary 18-OH components and 18 oxocortisol. RESULTS: Single dose (1.5 mg) dexamethasone led to a greater than 80% drop in aldosterone levels in the blood and urine, confirming the abnormal effect of ACTH on mineralocorticoid secretion. At the dose of 1 mg/d for 10 weeks, dexamethasone lowered mean 24-H ambulatory arterial pressure (11.8/9.6 mmHg) and corrected for the hypokaliaemia (+0.54 mmol/l) and the hyperaldosteronism (mean decrease -36% and -75% in blood and urine respectively). An adrenal tumour was identified in hyperplasic glands in two subjects and a micronodular formation was identified in two others. The specific molecular diagnosis of the disease was done with Southern blotting. Among the 18 families in 3 generations, 8 carried a 11 beta OHase-aldosterone synthetase chimeric gene. This mutation cosegregates with hormonal abnormalities and confirms the autosomal dominant inheritance of the disease. CONCLUSION: The simplicity and rapidity of genetic testing allows early diagnosis of this disease among families with early onset hypertension and associated hyperaldosteronism with or without adrenal hyperplasia and/or a tumoral formation.

Effects of glibenclamide on systemic and splanchnic haemodynamics in conscious rats.

1. The effects of the sulphonylurea, glibenclamide (20 mg kg-1, i.v.), at a dose that blocks vascular potassium channels, on systemic and splanchnic haemodynamics (radioactive microspheres) were studied in conscious rats. 2. Glibenclamide significantly decreased cardiac index and hepatic artery blood flow while it significantly increased vascular resistance in systemic, portal and hepatic arterial territories. 3. In rats with suppressed cardiovascular reflexes, glibenclamide induced vasoconstriction in systemic, portal and hepatic arterial territories. 4. Intracerebroventricular administration of glibenclamide did not alter systemic or regional vascular tone. 5. Glibenclamide blunted the vasodilator effect of the potassium channel opener, diazoxide but not that of the L-type calcium channel blocker, nicardipine. 6. Another sulphonylurea, glipizide (20 mg kg-1, i.v.), induced significant systemic and splanchnic vasoconstriction. 7. Thus, the glibenclamide-induced blockade of vascular potassium channels caused a vasoconstriction in the systemic and splanchnic vascular beds. In these territories, therefore, the opening of glibenclamide-sensitive potassium channels might be responsible for a basal vasodilator tone.

Suramin: an inhibitor of the final steps of the mineralocorticoid pathway?

The authors used incubated adrenal mitochondria to study the in vitro effect of suramin, an antiparasitic drug, on the transformation of corticosterone and 18-hydroxycorticosterone into aldosterone. The results show that, under conditions preserving membrane integrity, the "impermeance" of suramin meant that concentrations similar to the plasma-levels reached in treated patients induced only slight inhibition of the final intramitochondrial steps in aldosterone synthesis. However, suramin strongly inhibited mitochondrial respiration. The inhibition of two intramitochondrial mechanisms (respiration and steroid synthesis) suggests that the effect of suramin involves partial inhibition of metabolic intermediate carriers. The inhibition of the activity of various extramitochondrial enzymes involved in intermediate metabolism, suggests that the inhibition of steroid biosynthesis can be explained only on the basis of an extramitochondrial action of suramin. The action of suramin must, therefore, primarily and directly affect extramitochondrial steroid synthesis and only indirectly affect intramitochondrial steroid synthesis as a result of an impact on the reducing equivalent supply. However, even if suramin does not bind to cytochrome P450 11 beta which catalyzes the final steps of aldosterone biosynthesis pathway, this does not imply that suramin has no direct effect on steroid synthesis within the mitochondria, in addition to its toxic effects, particularly if the cell structure is disrupted (as is often the case in tumor tissues).

Hypoaldosteronism accompanied by normal or elevated mineralocorticosteroid pathway steroid: a marker of adrenal carcinoma.

In order to find a biochemical marker to assist the physician in the difficult differential diagnosis between malignant and nonmalignant adrenal tumors, plasma levels of the mineralocorticosteroids (deoxycorticosterone, 18-hydroxydeoxycorticosterone, corticosterone, 18-hydroxycorticosterone, and aldosterone) were determined. The same method (RIA which is preceded by a crucial separation step) was used to measure all these steroids including aldosterone. The subjects included 15 adults presenting various clinical signs of adrenocortical tumors (histopathologically: 6 with adrenal carcinoma, 1 with a history of adrenal carcinoma, 1 with adrenal metastasis from other forms of cancer, 6 with adenoma, and 1 with hyperplasia). The results show that both presurgery and during a recurrence of adrenal carcinoma, hypoaldosteronism occurs which contrasts with the normal or even elevated levels of some aldosterone precursors. In the 7 cases of adrenal cortical carcinoma, this dysfunction of the aldosterone pathway was detected regardless of the impairment of the other steroidogenesis pathways, whereas it was never found with a nonmalignant tumor. Despite the limited number of cases so far available, these findings suggest that detection of abnormalities of the aldosterone pathway, and particularly the detection of hypoaldosteronism by an assay method involving a crucial steroid separating step, could contribute to a differential diagnosis between benign and malignant adrenocortical tumor and between adrenal metastasis and other forms of cancer.

Cortisol and testosterone: inhibitory agents of the mineralocorticoid pathway. Is there a physiopathological meaning in adrenal tumors?

The authors incubated adrenal mitochondria to study the in vitro action of cortisol and testosterone on the transformation of corticosterone and 18-hydroxycorticosterone into aldosterone. The results show that cortisol at concentrations of 5 x 10(-6) and 10(-4) M inhibit the conversion of corticosterone into aldosterone by 23.6 to 90%; testosterone 5 x 10(-5) and 10(-4) M inhibit the reaction by 78.4 and 87.2%, respectively. The inhibition of the conversion of 18-hydroxycorticosterone into aldosterone is 12.5 to 91% by cortisol with concentrations ranging from 5 x 10(-7) to 5 x 10(-5) M and testosterone 5 x 10(-5) and 10(-4) M inhibits the reaction by 87.3 and 91%, respectively. Aldosterone (10(-8) and 10(-6) M) does not inhibit aldosterone biosynthesis from corticosterone or 18-hydroxycorticosterone. It thus appears that cortisol and testosterone have an effect on the aldosterone biosynthesis pathways in mitochondria. This action may be located at the binding site of the cytochrome P450 11 beta, which catalyzes all hydroxylation steps in the mineralocorticoid biosynthesis pathway. Because cortisol and testosterone may interfere with aldosterone biosynthesis, and since functional zonation is expected in adrenal carcinomas, the presence of these steroids in substantial amounts could explain the very low plasma aldosterone level usually observed, in adrenal carcinomas studied in our laboratory.

[Organ transplantation. One of the biochemical reasons for the race against the clock]. / Transplantations d'organes. Une des raisons biochimiques de la course contre la montre.

The authors have studied the subcellular functioning of human adrenal glands removed from subjects in a stage IV coma. The present study has a two-fold interest: on the one hand, it offers biochemical information on a key element in the intermediate metabolism (namely, the mitochondrial energetic metabolism, occurring in a fragile tissue which, under a state of shock, is primarily affected; the results obtained on such type of tissue may therefore be inferred to other organs); on the other hand, it allows a wider approach of the adrenal biochemical mechanisms during a stage IV coma. The mitochondrial fraction was obtained by differential centrifugation carried out immediately after organ removal. The steroid synthesis, studied using radioactive precursors, turned out to be similar to that found in other mammals. Respiratory characteristics, determined by polarography with a Clark oxygen electrode, at 37 degrees C, were satisfactory: respiratory intensity was 77.25 +/- 12.16 nanomoles O2/min/mg mitochondrial protein in the presence of succinate 15 mM and respiratory control was 1.93 +/- 0.15 in the presence of ADP 37 microM. The respiratory chain functioned in a classical manner: rotenone 25 microM did not inhibit respiration in the presence of succinate 15 mM, while it did with L-malate 15 mM. In the presence of succinate 15 mM, the respiratory intensity was inhibited at 87.4 percent and 76.7 percent by KCN 0.01 microM and antimycin A 0.09 microM respectively; with DNP 85 microM, it was multiplied by 5. However, the value of the P/O ratio was low (0.24 +/- 0.04). Under the present conditions, this may highlight the difficulty to synthetize ATP whenever neither the functioning nor the regulation of the multi-enzymatic complex accounting for oxygen consumption are affected. This result clearly confirms that the shortest possible delay between organ removal and transplantation is crucial, as the renewal of cell structures requires energy. These fundamental research studies account for the major concerns of reanimation teams. This also raises the issue of the role of fundamental researchers within a transplant surgery team.

Plasma levels of aldosterone precursors (including the 18-hydroxylated compounds in this synthesis pathway)--a tool for the analysis of adrenal disorders?

Some current ideas concerning the 18-hydroxylated corticosteroids (18-hydroxycorticosterone and 18-hydroxydeoxycorticosterone) and the other steroids of the mineralocorticosteroid pathway from deoxycorticosterone (DOC) are reviewed. Then, some recent findings from our own laboratory, obtained during the analysis of all aldosterone precursors from DOC in various adrenal disorders, such as enzyme deficiencies, and particularly adrenal masses detected in patients from various hospitals in France are discussed. The findings reported here show that these specialized assays can be valuable tools to determine adrenal function in complex cases.