High-renin malignant hypertension secondary to an aldosterone-producing adenoma

Malignant hypertension and high plasma renin activity was found in a 39-year-old woman with an aldosterone-producing adenoma. Only 3 similar cases have been previously reported, and all patients died before or after identification of the adenoma. The present paper documents the first reported case of a successfully managed high-renin malignant hypertension secondary to an aldosterone-producing adenoma. Regardless of its sporadic occurrence and common presence with low plasma renin activity, primary aldosteronism should be considered as a possible underlying cause of high-renin malignant hypertension.

Aldosterone-producing tumors (Conn's syndrome)

Adenomas of the adrenal cortex which produce aldosterone (APA) are among the surgically correctible causes of hypertension accounting for 0.5 to 1.0% of all hypertensive etiologies. The adenomas have a 5:1 predilection for women and generally present with hypertension or profound hypokalemia. A low plasma renin activity completes the triad for primary hyperaldosteronism which could be caused by adrenocortical cancer, a neoplasm with an average diameter of 12 cm, or idiopathic hyperaldosteronism (IHA), a bilateral hyperplasia of the zona glomerulosa of the adrenal cortex which responds poorly to surgical resection. The adenomas are small (2 cm) but can be localized by imaging or selective venous sampling. Resection has a high success rate with minimal morbidity.

Effects of ACTH on the last step of aldosterone biosynthesis

The production of tritiated aldosterone and tritiated SM (a saponifiable 18-hydroxycorticosterone derivative) by rat adrenals were studied at various incubation times in absence or presence of two concentrations of ACTH. Tritiated 18-hydroxycorticosterone or 18-deoxyaldosterone served as precursors. The lower ACTH concentration (150 pM) increased the production of tritiated aldosterone. Whereas, the higher ACTH concentration (1.5 microM) stimulated tritiated aldosterone production at shorter incubation time (30 min), while after 60 min it inhibited. This time dependency would reflect variations in the levels of endogenous steroids. On the other hand, the effects of ACTH on tritiated SM production were opposite to those on tritiated aldosterone. In effect, while 150 pM ACTH inhibited SM production, 1.5 microM ACTH stimulated it. These results suggest that ACTH promotes opposite effects on the productions of aldosterone and SM and therefore both productions would be coordinated under the regulation of ACTH.

Selective inhibition of angiotensin-II-mediated aldosterone secretion by 5-hydroxyeicosatetraenoic acid

We have previously demonstrated that the 12-lipoxygenase (12-LO) pathway plays a key role in angiotensin-II (AII)-dependent aldosterone production. In the present study we examined the role of the 5LO pathway on AII-induced aldosterone secretion in rat glomerulosa cells in vitro. The 5LO product 5-hydroxyeicosatetraenoic acid (5HETE) and its unstable precursor 5-hydroxyperoxyeicosatetraenoic acid did not significantly alter basal aldosterone secretion in concentrations from 10(-9)-10(-7) M. In contrast, 5HETE reduced peak AII-induced aldosterone production from 59.1 +/- 9.0 to 37.96 +/- 7.2 ng/10(6) cells (P less than 0.01). This was accompanied by inhibition of the AII-stimulated rise in 12HETE production (10(-9)M AII, 160 +/- 4% of control; 10(-9) M AII plus 10(-7) M 5HETE, 90 +/- 1% of control production). However, 5HETE had no effect on the aldosterone response to potassium or ACTH, secretagogues that cause no activation of the 12LO pathway. These results suggest that the 5LO product 5HETE can selectively modulate AII-dependent aldosterone secretion. Further, the selective inhibitory effect of 5HETE on the AII effect in rat glomerulosa cells may be exerted by blockade of arachidonate metabolism via the 12LO pathway. These results suggest that the 5LO pathway may negatively modulate AII action in the adrenal zona glomerulosa.

Tumor necrosis factor and interleukin-1 are potent inhibitors of angiotensin-II-induced aldosterone synthesis

Cytokines such as tumor necrosis factor (TNF) and interleukin-1 (IL-1), mediate many inflammatory and cellular responses. However, the effects of TNF and IL-1 on basal and angiotensin-II (AII)-stimulated aldosterone synthesis are not known. We studied the effect of recombinant and purified TNF and IL-1 on basal as well as AII-, ACTH-, and K+-induced aldosterone synthesis in isolated rat adrenal glomerulosa cells. Since we have previously shown that AII action is mediated by activation of the 12-lipoxygenase (12LO) pathway of arachidonic acid, we also evaluated the effects of these cytokines on the 12LO product 12-hydroxyeicosatetraenoic acid (12HETE) using a validated RIA technique. TNF at 2.5 and 5.0 ng/ml produced a dose-dependent inhibition of AII-induced aldosterone synthesis [AII, 39.0 +/- 3.3 ng/10(6) cells.h; AII plus TNF (5.0 ng/ml), 14.3 +/- 1.6; P less than 0.001 vs. AII; AII plus TNF (2.5 ng/ml), 24.7 +/- 3.2; P less than 0.01 vs. AII]. Similarly, TNF at 5.0 ng/ml also attenuated the stimulatory effect of ACTH (10(-9) M). However, K+-induced aldosterone synthesis was not altered. TNF also did not alter basal aldosterone levels. AII, as previously shown, stimulates 12HETE synthesis (basal, 608 +/- 114 pg/10(5) cells.h; versus AII, 1268 +/- 197; P less than 0.02). TNF at concentrations of 1.0-5.0 ng/ml produced a dose-dependent inhibition of AII stimulatory action on 12HETE synthesis [AII plus TNF (1.0 ng/ml), 650 +/- 26 pg, P less than 0.03 vs. AII; AII plus TNF (5.0 ng/ml), 390 +/- 46; P less than 0.01 vs. AII plus TNF (1.0 ng/ml)]. In addition, 12HETE at 10(-8) M completely restored the effects of AII during blockage by TNF. Purified human IL-1 (75% beta, 25% alpha) as well as recombinant human IL-1 beta at concentrations as low as 50 pg/ml inhibited AII-induced aldosterone synthesis. IL-1 beta did not alter ACTH- or K+-induced aldosterone synthesis and, in fact, had a tendency to potentiate ACTH effects. These results suggest that the cytokines TNF and IL-1 are potent inhibitors, particularly of AII action in the adrenal glomerulosa cell. Therefore, local or systemically produced TNF or IL-1 may be important negative modulators of aldosterone synthesis.

Inhibition of aldosterone secretion by atrial natriuretic peptide in chicken adrenocortical cells

Dispersed chicken adrenocortical cells were preincubated with atrial natriuretic peptide (rANP), sodium nitroprusside (SNP) or 8-bromo cyclic GMP, followed by incubations with ACTH, chicken PTH, cholera toxin or various steroid intermediates of aldosterone production. Cyclic AMP production and aldosterone secretion were evaluated, in order to determine the sites of ANP inhibition in the sequence of events leading to aldosterone secretion. Dose-dependent inhibitory effects on ACTH-stimulated aldosterone secretion by rANP and SNP were observed. Both agents appeared to stimulate cGMP production by the particulate fraction of the avian adrenocortical cells. Aldosterone production, stimulated by cyclic AMP agonists such as ACTH, chicken PTH and cholera toxin, was significantly inhibited by ANP. On the other hand, ANP did not interfere with production or degradation of cAMP. Each of the aldosterone intermediates--pregnenolone, progesterone, 11-deoxycorticosterone and corticosterone--promoted aldosterone production when included in the incubation media. Atrial natriuretic peptide and SNP inhibited aldosterone secretion when enhanced by the intermediates, by about 40-60%, but the ACTH-stimulated secretion was inhibited by over 90%. The results suggest two sites of inhibition by ANP in the pathway of aldosterone synthesis and secretion: synthesis of cholesterol or pregnenolone, and conversion of corticosterone to aldosterone. The inhibition by 8-bromo cGMP of aldosterone secretion and the similar sites of inhibition for ANP and SNP suggest that cyclic GMP mediates the inhibition in both cases.

Purification and characterization of two distinct forms of rat adrenal cytochrome P450(11) beta: functional and structural aspects

It is generally accepted that the last three steps of aldosterone biosynthesis are catalyzed by a single enzyme, i.e., cytochrome P450(11) beta (P450XIB). We have previously reported that rat adrenal mitochondria may be capable of producing two forms of P450(11) beta which differ in molecular weight (49 and 51 kDa). In the present study we describe the purification, the enzymatic activities, and some structural properties of these two proteins. Using zona fasciculata mitochondria, the 51-kDa protein was purified to electrophoretic homogeneity by means of octyl-Sepharose chromatography. In a reconstituted system the protein catalyzed 18- and 11 beta-hydroxylation of deoxycorticosterone, but exhibited no 18-hydroxylation or 18-hydroxydehydrogenation of corticosterone. The 49-kDa protein was isolated from zona glomerulosa mitochondria of rats kept on a low-sodium, high-potassium regimen. Using octyl-Sepharose chromatography, it could be separated from the 51-kDa protein. A reconstituted eluate fraction, containing the 49-kDa protein, converted deoxycorticosterone not only to 18-OH-deoxycorticosterone and corticosterone, but also to 18-OH-corticosterone and aldosterone. These findings indicate that the rat adrenal cortex is capable of producing two distinct forms of active cytochrome P450(11) beta. A structural relationship of the 49- and 51-kDa proteins was indicated by experiments involving limited proteolysis. Thus, digestion with alpha-chymotrypsin and V8-protease yielded very similar peptide maps for both proteins. During potassium repletion of potassium-deficient rats, the disappearance of the active 51-kDa protein coincided with the appearance of the 49-kDa protein. These results are suggestive of a post-translational processing mechanism converting the 51-kDa protein into the smaller 49-kDa form. However, the 49-kDa protein might also be encoded by a distinct gene, regulated separately depending on the physiological conditions.

The new aromatase inhibitor CGS-16949A suppresses aldosterone and cortisol production by human adrenal cells in vitro

CGS-16949A is a new orally active nonsteroidal aromatase inhibitor which is more than 100-fold more potent than aminoglutethimide. This compound is an imidazole derivative, and therefore, its possible effect on cytochrome P-450-dependent enzyme activities in the adrenal gland was evaluated. In vitro investigations with dispersed normal and hyperplastic human adrenocortical cells showed that CGS-16949A at 10(-7)-10(-6) M is a potent 11 beta-hydroxylase inhibitor, which inhibits ACTH-stimulated cortisol release to a similar extent as an equimolar concentration of metyrapone (IC50 for both compounds, 10(-7)-5 X 10(-7) M). Etomidate was a more potent 11 beta-hydroxylase inhibitor (IC50, approximately 10(-8) M), while 10(-7)-10(-6) M ketoconazole caused (via 17 alpha-hydroxylase inhibition) a similar inhibition of cortisol release as 10(-7) M CGS-16949A (IC50, 10(-7)-5 X 10(-7) M). The 11 beta-hydroxylase inhibition by CGS-16949A was accompanied by a dose-dependent increase in the release of precursor steroids by the adrenocortical cells in vitro, including deoxycortisol, 17-hydroxyprogesterone, and androstenedione. Aldosterone release was suppressed 50% by 10(-9) M CGS-16949A, while the IC50 for cortisol in the same cells was 10(-7) M. Aldosterone release by the dispersed adenoma cells obtained from a patient with primary aldosteronism was also significantly suppressed by CGS-16949A. We concluded that 1) the new nonsteroidal aromatase inhibitor CGS 16949A is an inhibitor of 11 beta-hydroxylase which is equipotent to metyrapone. At present it is unclear whether the compound at the dose that causes complete aromatase inhibition in vivo also affects stress-induced cortisol release in man. 2) CGS-16949A exerts a very potent inhibitory effect on normal aldosterone release (IC50, 10(-9) M) and on tumorous aldosterone secretion. CGS-16949A might, therefore, be a drug that can be used in the treatment of primary hyperaldosteronism.

Proteolytic activation of aldosterone biosynthesis in rabbit adrenal capsular cells by alpha-chymotrypsin

The effect of chymotrypsin on aldosterone biosynthesis by dispersed rabbit adrenal capsular cells was examined. Bovine alpha-chymotrypsin at concentrations of 10(-7) to 10(-5) M stimulated aldosterone production, and human chymotrypsin had an even stronger stimulatory effect. Bovine trypsin had no effect on aldosterone production by adrenal cells. Chymotrypsin treatment did not change the sensitivity of the adrenal cells to ACTH or angiotensin II. These results suggest the existence of unique chymotrypsin-susceptible sites on rabbit adrenal capsular cells, the digestion of which results in stimulation of aldosterone biosynthesis.

Effects of prolonged cyclosporine-A treatment on the morphology and function of rat adrenal cortex

The effects of prolonged (30 day) treatment with daily therapeutical doses of cyclosporine A (CSA) (20 mg/kg) on the function and morphology of adrenal cortex were studied in adult male rats. CSA-treated animals developed a notable hypertension, along with a striking rise in PRA, which was not coupled with significant changes in the plasma concentrations of aldosterone and corticosterone (hyperreninemic hypoaldosteronism). Morphometry showed that zona glomerulosa (ZG) and zona fasciculata, and their parenchymal cells were atrophic. Isolated capsular (ZG) and inner (zona fasciculata/reticularis) cells displayed reduced basal and stimulated secretory responses. However, while the response of ZG cells to angiotensin II was almost completely suppressed (96%), basal steroid secretion of isolated cells, as well as the aldosterone and corticosterone response of ZG cells to potassium and ACTH, and corticosterone production of inner cells in response to ACTH were decreased by only about 30-40%. The hypothesis is advanced that CSA exerts a dual effect on rat adrenal cortex: 1) a general inhibitory effect on the growth and steroidogenic capacity of adrenocortical cells, which manifests itself only after very prolonged treatment and may be caused by an impairment of protein synthesis; and 2) an acute effect involving the specific blockade of the angiotensin-II-induced stimulation of the secretory activity of ZG cells.

Endothelin binding to cultured calf adrenal zona glomerulosa cells and stimulation of aldosterone secretion

Endothelins are a group of potent vasoconstrictors whose structure was deduced from genomic DNA. ET-1 was first isolated from culture supernatants from porcine endothelial cells and ET-3 was identified from a rat DNA library. We report on the binding of 125I-ET-1 to zona glomerulosa cells in culture and on its ability to stimulate aldosterone secretion. Cultured calf adrenal zona glomerulosa cells have saturable, high affinity [Kd = 1.00 +/- 0.17 X 10(-10) M (SEM)] receptors which bind ET-1 in a temperature and time dependent manner. Binding was specific and angiotensin II, vasopressin, ANP, BNP, apamin, calcium channel agonists or antagonists did not interact with the receptor. ET-3 displaced 125I-ET-1 from the receptor with a relative potency of 0.39 +/- 0.1% (SEM) that of ET-1. ET-1 incubated with cultured glomerulosa cells stimulated aldosterone secretion in a dose dependent manner but it was less potent than angiotensin II. ET-3 had less than 1% the relative potency of ET-1 stimulating aldosterone secretion. This data suggest that ET-1 is an independent stimulator of aldosterone secretion and we are speculating that it might be important in those situations, like in malignant hypertension, where endothelial damage might result in increased ET-1 production.

Studies on the mechanisms of ACTH-induced inhibition of aldosterone biosynthesis in the rat adrenal cortex

In rats, chronic treatment with high doses of ACTH (10-40 micrograms/100 g body weight per day) leads to a marked reduction in aldosterone synthesis by adrenal capsules. The possibility that this inhibition is secondary to a decrease in plasma potassium levels or in renin angiotensin system (RAS) activity has been explored. The effects of chronic ACTH treatment were compared in (I) animals in which the endogenous RAS activity was stimulated by restricting dietary sodium intake, (II) animals in which plasma angiotensin II was increased by infusion from implanted osmotic minipumps and (III) animals which received supplementary potassium and in which hypokalaemia was prevented. In all cases, rates of aldosterone biosynthesis in vitro by adrenal capsules were decreased in ACTH-treated animals to an extent similar to those in untreated controls. In addition, ACTH treatment of hypophysectomized rats resulted in a similar inhibition of aldosterone biosynthesis to that found in sham-operated controls. It may be concluded that the ACTH-induced reduction of aldosterone biosynthesis is independent of the secretion of other pituitary hormones, and cannot be simply ascribed to either a reduction in RAS activity or in plasma potassium levels. The results are consistent with the view that the effects of chronic ACTH treatment are mediated by a direct action on the zona glomerulosa cell, which leads to its transformation into a zona fasciculata-like form.

Adrenal cytochrome P-45011 beta-proteoliposomes catalyzing aldosterone synthesis: preparation and characterization

Purified cytochrome P-45011 beta from bovine adrenocortical mitochondria was successfully incorporated into the liposome membranes composed of phosphatidylcholine, phosphatidylethanolamine and cardiolipin at a molar ratio of 2:2:1. The incorporation of P-45011 beta into the liposome membranes was ascertained by the Ficoll density gradient centrifugation and the protein refractoriness to trypsin digestion. The prepared proteoliposomes containing P-45011 beta and phospholipid at a molar ratio of 1:3000 were unilamellar vesicles of about 40 nm in average diameter. The P-45011 beta embedded in the liposome membranes was found to be more stable than the detergent-solubilized form. The reconstituted system containing the P-45011 beta-proteoliposomes, adrenodoxin and NADPH-adrenodoxin reductase showed catalytic activities not only for the hydroxylation of 11-deoxycorticosterone at 11 beta- and 18-positions but also for its conversion into aldosterone with a turnover number of 2.3 nmol/min per nmol of P-45011 beta. A successive reaction without the intermediates leaving from the enzyme was suggested for the P-45011 beta-mediated conversion of 11-deoxycorticosterone to aldosterone following the result that the formation of aldosterone was linear with respect to time without the lag phase; this was confirmed by the result that radioactivity in aldosterone from 3H-labeled 11-deoxycorticosterone was scarcely decreased by the addition of unlabeled intermediates to the reactions system.

Biochemical effects of prolonged renin inhibition in marmosets

The renin inhibitor CGP 29,287 was administered continuously for 7 days (30 mg/kg per day, intraperitoneally, via osmotic minipumps) to normotensive marmosets fed a low-salt diet. As a control, another group of marmosets was given vehicle only. After 7 days of treatment, the mean arterial blood pressure of the CGP 29,287-treated marmosets was significantly lowered by about 23 mmHg. Plasma immunoreactive total and active renin were increased 10- and sevenfold, respectively, whereas plasma renin activity (PRA) was reduced by 95%. Plasma angiotensin II (Ang II) and aldosterone were also reduced (by 97 and 85%, respectively). Serum angiotensin converting enzyme activity was unchanged and there were no differences in plasma concentrations of electrolytes, urea or creatinine between CGP 29,287-treated and control marmosets. These results indicate that although renin release is markedly stimulated after continuous administration of a renin inhibitor for 7 days, the formation of Ang II and aldosterone, the active hormones of the renin-angiotensin system, is substantially reduced.

Atrial natriuretic factor during fetal and postnatal life: a review

This review summarizes current understanding of the role of atrial natriuretic factor (ANF) during fetal and postnatal life. The cardiac localization of ANF synthesis changes during development from ventricular to predominantly atrial cardiocytes. ANF is present as a circulating hormone during fetal life and fetal plasma ANF clearance rates and production rates are higher than in adults. ANF is a natriuretic hormone in fetal and newborn animals. However, unlike the adult, this natriuresis does not appear to be related to suppression of the renin-angiotensin system. During fetal life, ANF levels can be increased through both atrial distension and humoral influences. Hence, mechanisms of ANF release during development appear to be similar to those present at maturity.

Effect of the benzodiazepines diazepam, des-N-methyldiazepam and midazolam on corticosteroid biosynthesis in bovine adrenocortical cells in vitro; location of site of action

Diazepam and midazolam inhibited cortisol and aldosterone synthesis in bovine adrenal cells in vitro. The biologically active metabolite des-N-methyldiazepam did not. Midazolam was a more potent inhibitor (IC50: 6 micrograms/ml) than diazepam (IC50: 13 micrograms/ml) in ACTH-stimulated cells. Both compounds inhibited steroidogenesis at several points in the biosynthetic chain; the greatest effects were on 17 alpha hydroxylation and 21 hydroxylation. Diazepam had a relatively greater effect on 17 alpha hydroxylation; midazolam on 21 hydroxylation. Both were less potent inhibitors of 11 beta hydroxylation and had little apparent effect on side chain cleavage. Thus microsomal hydroxylation is more vulnerable to benzodiazepines than mitochondrial hydroxylation. It is suggested that the drugs act by competing with steroid mixed function oxidases for cytochrome P-450. The plasma concentrations required for these effects are high in relation to therapeutic levels but may be achieved, for example, during acute infusions or when they are used in combination with imidazole drugs such as cimetidine.

Content and biosynthesis of cortisol in aldosterone-producing adenomas

The content and biosynthesis of aldosterone and cortisol were examined and compared in the aldosterone-producing adenomas and adjacent adrenal glands from patients with primary aldosteronism that resulted from solitary, benign adrenocortical tumors (0.8 to 32.3 gm). Histologic examination of the six aldosterone-producing adenomas studied confirmed a predominance of cells resembling zona fasciculata rather than zona glomerulosa, as reported in previous studies. Measurement by radioimmunoassay of the tissue content of steroids preformed in vivo demonstrated that aldosterone was present in concentrations 8 times higher in aldosterone-producing adenomas (1.5 +/- 0.5 micrograms/gm tissue; mean +/- SEM) than in adrenal glands (0.2 +/- 0.06 micrograms/gm tissue). Cortisol concentration in aldosterone-producing adenomas (5.4 +/- 1.4 micrograms/gm tissue) was approximately one third that in adrenal glands (15.8 +/- 6.3 micrograms/gm tissue), but cortisol was by far the major steroid in both types of tissue. In vitro, the most important metabolic product quantitatively from 4-carbon 14-labeled cholesterol incubated with mitochondria plus microsomes and from 4-14C-labeled pregnenolone incubated with tissue slices was cortisol, formed in a time-dependent manner in both types of preparations; cortisol synthesis greatly exceed that of aldosterone in adrenal glands, but even in aldosterone-producing adenomas the formation of cortisol was at least 5 times greater than that of aldosterone. The fasciculata structure and dual biosynthetic capacity of aldosterone producing adenomas for cortisol and aldosterone are interpreted in the light of developing concepts of the roles of adrenocorticotropic hormone and of alterations in the microenvironment of the cell in the zonal differentiation of the normal adrenal cortex.(ABSTRACT TRUNCATED AT 250 WORDS)

Physiology of the adrenal cortex

Knowledge of the functional morphology and physiology of the adrenal cortex and of the regulation of its secretory products is essential to understanding the meaning of the results of various tests in the diagnosis of adrenocortical disease and to providing the postoperative care necessary to correct this condition. Removal of a cortisol-producing adenoma will necessitate replacement of glucocorticoids only, whereas after resection of an aldosterone-producing adenoma, no steroid replacement will be required.

Isolation of aldosterone synthase cytochrome P-450 from zona glomerulosa mitochondria of rat adrenal cortex

A cytochrome P-450 capable of producing aldosterone from 11-deoxycorticosterone was purified from the zona glomerulosa of rat adrenal cortex. The enzyme was present in the mitochondria of the zona glomerulosa obtained from sodium-depleted and potassium-repleted rats but scarcely detected in those from untreated rats. It was undetectable in the mitochondria of other zones of the adrenal cortex from both the treated and untreated rats. The cytochrome P-450 was distinguishable from cytochrome P-45011 beta purified from the zonae fasciculata-reticularis mitochondria of the same rats. Molecular weights of the former and the latter cytochromes P-450, as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, were 49,500 and 51,500, respectively, and their amino acid sequences up to the 20th residue from the N terminus were different from each other at least in one position. The former catalyzed the multihydroxylation reactions of 11-deoxycorticosterone giving corticosterone, 18-hydroxydeoxycorticosterone, 18-hydroxycorticosterone, and a significant amount of aldosterone as products. On the other hand, the latter catalyzed only 11 beta- and 18-hydroxylation reactions of the same substrate to yield either corticosterone or 18-hydroxydeoxycorticosterone. Thus, at least two forms of cytochrome P-450, which catalyze the 11 beta- and 18-hydroxylations of deoxycorticosterone, exist in rat adrenal cortex, but aldosterone synthesis is catalyzed only by the one present in the zona glomerulosa mitochondria.

Production of renin, angiotensin II, and aldosterone by adrenal explant cultures: response to potassium and converting enzyme inhibition

The existence of renin in a number of extrarenal tissues has been well documented, but the physiological role of extrarenal renin remains unknown. To study the physiological role of adrenal renin, we developed a serum-free culture system for adrenal capsular/zona glomrulosa explants. Explants showed good viability in culture (greater than 80%), and demonstrated net production of aldosterone, angiotensin II, and prorenin. Aldosterone production was consistently stimulated by an increase in potassium (6 mM) in the culture medium. Both aldosterone and angiotensin II production could be attenuated by adding the angiotensin converting enzyme inhibitor lisinopril to the culture medium (0.1 mM). These data suggest that rat adrenal explants are capable of producing all of the components of a functional renin-angiotensin-aldosterone system and that these components can interact in response to physiological stimuli. These findings support the hypothesis that a local adrenal renin system may play a physiological role in the control of adrenal aldosterone production.

[Isolation and fractionation in percoll gradient of guinea pig adrenal cortex cells and their functional characteristics]

Suspension of isolated adrenal cells from the guinea pig adrenals was prepared using two modifications of collagenase dispersion. The cells separated by percoll density gradient gave 4 bands. The fraction of adrenocorticocytes has buoyant density of 1.03-1.05 g/ml. The lower bands comprise blood cells with density of 1.07-1.10 g/ml. The aldosterone content in the adrenocorticocyte fraction is 1200-1300 pg/10(5) cells. Intensity of labelling of cellular proteins increases only in the adrenocorticocyte fraction in response to a rise in K+ concentration in incubation medium. The Scatchard plot method was used to characterize binding of 125I-ACTH to dispersed adrenocortical cells. Binding association constant (Ka) and binding capacity (Bmax) are 1.3 X 10(8) M-1 and 2.0 X 10(-9) mol/l, respectively. A relation between functional activity of adrenocortical cells, their ultrastructural features and density is discussed.

18-Substituted progesterone derivatives as inhibitors of aldosterone biosynthesis

The synthesis of new progesterone derivatives substituted at the 18 methyl group is described. These compounds are designed as 18-monooxygenase, cytochrome P-450-dependent potential kcat inhibitors. Preliminary results on the in vitro biological investigation of these modified progesterones are presented.

Hyperfunctioning and nonhyperfunctioning benign adrenal cortical lesions: characterization and comparison with MR imaging

The authors evaluated the potential of magnetic resonance (MR) imaging at 0.35 T to permit differentiation of nine hyperfunctioning adrenal cortical lesions from 21 nonhyperfunctioning adrenal cortical adenomas. Both qualitative data (visual assessment) and quantitative data (signal intensity ratios, T1, and T2) were used for tissue characterization. With a 2,000/56-100 sequence (repetition time msec/echo time msec), the majority of lesions were visually isointense to liver. Of 34 quantitative measures, only lesion-liver and lesion-kidney intensity ratios at 2,000/150 showed statistically significant differences among nonhyperfunctioning adenomas, aldosterone-producing lesions, and corticosteroid-producing lesions; however, the authors question the significance of these differences because of the abundant noise associated with the 2,000/150 sequence. The results suggest that nonhyperfunctioning adrenal cortical adenomas cannot be distinguished from benign hyperfunctioning cortical lesions with use of MR imaging at 0.35 T.

[An assay for aldosterone precursors: a tool for clinical diagnosis and adrenal physiopathology]

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.