The final step of aldosterone biosynthesis requires reducing power. It is not a dehydrogenation.

A mitochondrial preparation from adult duck adrenal gland was used to study the mechanism (dehydrogenation or other) of the last step of aldosterone biosynthesis (18-oxidation) by incubation of tritiated 18-hydroxycorticosterone. Results show that the role of citric acid cycle metabolites is to provide reducing power. When reducing power is provided by malate, which yields NADH or NADPH directly, the reoxidation of reduced coenzymes in the oxidative phosphorylation chain is not necessary. In the presence of succinate, the oxidative phosphorylation chain is required, but only to provide ATP. Stimulation of the reaction by low concentrations of KCN in the presence of malate shows that the reducing power is not used in the oxidative phosphorylation chain. These data suggest that the reaction is not a dehydrogenation and that the reducing power is used in a pathway competing with the respiratory chain, most probably a hydroxylating pathway, in mitochondria.

Impact on energy metabolism of quantitative and functional cyclosporine-induced damage of kidney mitochondria.

In this study we have measured, under experimental conditions which maintained efficient coupling, respiratory intensity, respiratory control, oxidative phosphorylation capacity and protonmotive force. Succinate cytochrome-c reductase and cytochrome-c oxidase activities were also studied. These investigations were carried out using kidney mitochondria from cyclosporine-treated rats (in vivo studies) and from untreated rats in the presence of cyclosporine (in vitro studies). Inhibition of respiratory intensity by cyclosporine did not exceed 21.1% in vitro and 15.9% in vivo. Since there was no in vitro inhibition of succinate cytochrome-c reductase and cytochrome-c oxidase activities, the slowing of electron flow observed can be interpreted as a consequence of an effect produced by cyclosporine between cytochromes b and c1. Cyclosporine had no effect on respiratory control either in vitro or in vivo. Statistically significant inhibition of the oxidative phosphorylation was observed both in vitro (6.6%) and in vivo (12.1%). Moreover, cyclosporine did not induce any change of membrane potential either in vivo or in vitro. Our findings show that cyclosporine is neither a protonophore, nor a potassium ionophore. In cyclosporine-treated rats we notices a decrease of protein in subcellular fraction, including the mitochondrial fraction. The role of the inhibition respiratory characteristics by cyclosporine in nephrotoxicity in vivo must take account of these two parameters: inhibition of the respiratory characteristics measured in vitro and diminution of mitochondrial protein in cyclosporine-treated rats.

Stimulation of oxygen consumption at the cytochrome A3 level inhibits aldosterone biosynthesis from 18-hydroxycorticosterone.

A mitochondrial preparation from duck adrenal gland was used, under aerobic conditions, to show that the oxygen requirement for the last step of aldosterone biosynthesis (transformation of 18-hydroxycorticosterone into aldosterone) is at the cytochrome P-450 level only. Vitamin C and tetramethyl-p-phenylene-diamine (TMPD) were used to increase oxygen consumption at the cytochrome a3 level, thereby decreasing its availability to cytochrome P-450. The vitamin C plus TMPD system acts as an 'oxygen trap'. Results show that despite reducing equivalents provided by L-malate, vitamin C plus TMPD strongly inhibits aldosterone biosynthesis from 18-hydroxycorticosterone (89%). Moreover, we used KCN in order to block oxygen consumption, even in the presence of vitamin C plus TMPD. Under these conditions, the inhibition of aldosterone biosynthesis from 18-hydroxycorticosterone is reduced by 51%. The reversal of this inhibition by KCN was evident but only partial. According to polarographic and electron microscopy studies, the reversal of inhibition can only be explained by an increased availability of oxygen at the cytochrome P-450 level. Experiments performed under aerobic conditions, without a nitrogen atmosphere, show that oxygen is required in the transformation of 18-hydroxycorticosterone into aldosterone, at the cytochrome P-450 level. This suggests that a classical hydroxylating mechanism is involved.

The effects of fadrozole hydrochloride on aldosterone secretion in healthy male subjects.

The aim of this double blind placebo-controlled cross-over study was to evaluate the effects of fadrozole, a new oral nonsteroidal aromatase inhibitor, on basal and stimulated cortisol and aldosterone secretion at a daily dosage of 4 mg given for 14 days to eight healthy men. After 2 weeks of treatment, fadrozole, compared with placebo, effectively suppressed plasma estrogen levels (P less than 0.05 at 0800 h), but did not affect glucocorticoid secretion either under basal conditions or after stimulation with ACTH. Basal plasma aldosterone levels were not significantly different with fadrozole treatment compared to those after placebo treatment. However, compared with pretreatment values, basal aldosterone secretion appeared impaired (P less than 0.05). A statistically significant blunting of the responses of plasma aldosterone to ACTH (P less than 0.01) and upright posture (P less than 0.01) after fadrozole compared with placebo treatment further indicated that fadrozole impaired basal aldosterone secretion. This attenuation of aldosterone secretion was accompanied by a rise of PRA in the basal condition (P = 0.05) and after stimulation by 40 mg furosemide (P less than 0.01) and upright posture (P less than 0.01). An increase in deoxycorticosterone was observed after fadrozole treatment compared with pretreatment values (P less than 0.01) and after stimulation with ACTH compared with placebo (P less than 0.05). This study confirms that fadrozole given in daily doses of 4 mg is an effective aromatase inhibitor which does not affect glucocorticoid secretion. However, this dose may induce an impairment of aldosterone secretion which is modest and revealed mainly under specific stimulatory conditions, and does not lead to clinical symptoms of hemodynamic dysregulation or a relevant disturbance of serum electrolytes.

Relation between energy metabolism in mitochondria and conversion of 18 hydroxycorticosterone to aldosterone in adrenals.

The purpose of this study was to see whether there was any link between conversion of 18 hydroxycorticosterone to aldosterone and mitochondrial energy metabolism. In vitro incubations of duck adrenal mitochondria with 18 OH B were used in this study. Results show that 18 oxidation is inhibited by compounds blocking electron transport (antimycin A, cyanide, rotenone, amytal). Inhibition induced by cyanide and antimycin A is reversed with ATP. 2,4 dinitrophenol, oligomycin and DCCD inhibit 18 oxidation but guanidine stimulate this reaction. Thus aldosterone synthesis from 18 OH B depends on energy metabolism in mitochondria. This is a very new aspect related to the last step of aldosterone synthesis.

[Cytochrome P-450 and transformation from 18-hydroxycorticosterone to aldosterone]. / Cytochrome P450 et transformation de la 18 hydroxycorticostérone en aldostérone.

The authors have studied the in vitro conversion of 18 hydroxycorticostérone to aldosterone (18 oxidation) by duck adrenal subcellular fractions. Considering the new hypothesis about the mechanism of this step (hydroxylation mechanism) the authors have investigated a possible relationship between this reaction and cytochrome P450. With experimental conditions described, data show that metyrapone, a cytochrome P450 competitive inhibitor does not inhibit 18 oxidation. In contrast, 18 oxidation is inhibited by spirolactones (spironolactones, canrenone, potassium canrenoate). These compounds act at the cytochrome P450 level but have also an uncoupling effect which has been recently discovered. The effects of metyrapone and spirolactones on 18 oxidation as well as the different behaviour between biologicaly and organically synthetised 18 hydroxycorticosterone allow us to propose hypotheses for the mechanism of this step.

[Enzymatic character and subcellular localization of the transformation reaction of 18 hydroxycorticosterone to aldosterone]. / Caractère enzymatique et localisaiton subcellulaire de la réaction de transformation de la 18 hydroxycorticostérone en aldostérone.

The authors study in vitro the conversion of 18 hydroxycorticosterone into aldosterone in duck adrenal subcellular fractions. The enzymatic nature of this conversion is studied by classical enzymologic tests. All results are in favor of an enzymatic conversion and this enzyme is strictly located in the mitochondrial fraction. Results concerning this localisation are expressed as specific activity and relative specific activity. Preliminary results on further experimental data point out that this conversion depends on the energetic state of mitochondria. Complete electron transfer blokage inhibits this transformation whereas respiratory chain blokage with a NADPH generating system and ATP supplementation does not seem to produce any inhibition. Oligomycine and guanidine stimulation suggest that ATP or its precursors may be involved in this reaction.

[Antialdosterones and enzymes of the adrenal gland]. / Antialdostérones et enzymes de la surrénale.

With subcellular fractions of animal adrenals, the authors have looked for the effect of antialdosterones on different aspects of adrenal metabolism (steroidogenesis, some enzymes of intermediary metabolism, mitochondrial respiration). Antialdosterones act on mitochondrial respiration by inducing an uncoupling effect. Nature of this uncoupling cannot yet by precised. Antialdosterones inhibit steroidogenesis with concentrations corresponding to blood concentrations observed during treatment with these compounds. This inhibition could explain the annulation of hyperaldosteronism secondary to sodium loss and kaliemic replenishment. This enhance the interest of antialdosterones over other diuretics.

[Arterial hypertension in heart transplant patients treated with cyclosporin]. / Hypertension artérielle des transplantés cardiaques traités par la ciclosporine.

Amongst 40 patients undergoing cardiac transplantation between 1981 and 1984 and treated with cyclosporin A, 23 had hypertension. Fifteen of these patients, aged 39 years (16-57 years), without cardiac failure, treated with 8 +/- 3 mg kg-1 d-1 of cyclosporin A and 0.27 +/- 0.1 mg kg-1 d-1 of prednisolone were studied on average 288 days after transplantation (63-788 days). Blood pressure in the out-patients department of these 15 patients was 164 +/- 14/112 +/- 13 mmHg, in the absence of any antihypertensive treatment for more than 15 days, with a urinary sodium of 104 +/- 48 mEq/d and a urinary potassium of 55 +/- 13 mEq/d (mean +/- standard deviation). Two abnormalities accompany the raised blood pressure: a reduced creatinine clearance of 63 +/- 30 ml min-1 and an increased plasma volume of 445 +/- 686 ml (p less than 0.05) with reference to Hurley's norms (1975). By contrast, urinary excretion of VMA and metanephrines were invariably normal. Plasma renin activity (PRA) was normal in a lying position (1.02 +/- 0.42 ng ml-1 h-1) and after orthostatic stimulation (2.55 +/- 1.31 ng ml-1 h-1). Renin release was not stimulated by acute inhibition of converting enzyme (1.11 +/- 0.70 ng ml-1 h-1). Plasma aldosterone (110 +/- 52 pg ml-1), plasma angiotensinogen (924 +/- 213 ng/ml) and converting enzyme activity (30 +/- 6 mU ml-1) were normal. In these patients with a denervated heart, the orthostatic position increased heart rate from 85 +/- 11 to 93 +/- 12 beats/min.(ABSTRACT TRUNCATED AT 250 WORDS)

[Effect of spironolactones on aldosterone synthesis and adrenal metabolism]. / Action des spironolactones sur la synthèse de l'aldostérone et sur le métabolisme surrénalien.

The authors study antialdosterones action on several enzymatic systems in subcellular fractions of animal adrenals. They report an inhibition of aldosterone synthesis located at the corticosterone 18 hydroxylation step but also at the following step of oxydation of 18 hydroxycorticosterone into aldosterone (in the duck as well as in the sheep). In contrast, these drugs do not modify the activity of several enzymes not involved in aldosterone biosynthesis. In addition, anti-aldosterones have decoupling action on mitochondrial respiration. This effect, observed by many authors on adrenal mitochondria can be considered as an illustration of competition between two electron transport chains (phosphorylative oxydation and hydroxylation) and not as a toxic effect. These in vitro results are of clinical interest as they are obtained with antialdosterones concentrations similar to that found in plasma of subjects treated with these diuretics and could explain the absence of secondary hyperaldosteronism in these subjects.

[Cardiac transplantation. Selection of patients and long-term results]. / Transplantation cardiaque. Choix des patients et résultats à long terme.

Performed for the first time in the world, in December 1967, by Barnard in Capetown, and for the first time in Europe by our team in April 1968, cardiac transplantation has now 20 years of clinical applications. A best selection of the recipients, a more precise selection of donors, refinements in surgical technique, a better and earlier diagnosis of post-operative complications, more effective therapeutic means especially cyclosporin, have brought us, from 1981, such major improvements that many teams were prompted to resume the procedure. In our experience of more than 400 transplants at La Pitié Hospital, a five-year follow-up shows that 70 p. cent of the patients are alive, having resumed a normal familial, social, professional and often sporting life. Much progress remains to be achieved, but this procedure now seems to be quite common if not routine, only limited by the insufficient number of donors.

[18-Hydroxycorticosterone, 18-hydroxydesoxycorticosterone. Why, when, how to determine plasma levels in some adrenal pathologies]. / 18-Hydroxycorticostérone, 18-hydroxydésoxycorticostérone. Pourquoi, quand, comment en déterminer les taux plasmatiques dans certaines pathologies surrénaliennes.

The authors review some current ideas concerning the role of 18-hydroxylated corticosteroids as mineralocorticoids themselves and as possible precursors of the principal mineralocorticoid, aldosterone. In particular, the physiological and pharmacological agents affecting their secretion are discussed together with a description of the methods used for their analysis in plasma in the department of Clinical Biochemistry Pitié-Salpétrière. Finally, the value of these assays in the differential diagnosis of mineralocorticoid hypertension and inborn errors of corticosteroid biosynthesis is assessed and the constraints on sampling technique listed.

[An assay for aldosterone precursors: a tool for clinical diagnosis and adrenal physiopathology]. / Dosage des précurseurs de l'aldostérone: intérêt diagnostique et physiopathologique.

After their contribution to the study of 18 hydroxycorticosterone as an intermediate in aldosterone biosynthesis the authors present here a new series of assays for the measurement of plasma aldosterone precursors as a pertinent tool in the extensive study and clinical evaluation of the mineralocorticoid function of the adrenal. These radioimmunoassays must be undertaken under strict technical conditions: time of blood withdrawal and also posture. Their use is irrelevant in any other clinical feature but the salt loss syndrome and hyper mineralo-corticism together with or without high plasma aldosterone.