Renin, renin substrate and angiotensin II concentration in renal venous blood

In 22 hypertensive patients with unilateral renal artery stenosis (RAS) and in 8 patients with unilateral or bilateral renal or renal arterial disease, plasma renin activity (PRA), renin substrate (PRS), and angiotensin II (AT II) concentrations were measured in both renal veins and in a peripheral vein 1-2 h after stimulation of renin secretion by injection of frusemide. In patients with elevated PRA in venous blood from a kidney with RAS, AT II was either also elevated, lower than or equal to PRA in peripheral blood, while the contralateral kidney almost invariably extracted AT II. In the 8 patients with variable renal diseases, the concordance between PRA and AT II measurements was better. Results suggest that AT II measurements in renal venous blood are less useful in assessing the functional significance of a RAS than those of PRA. Since PRS is not different in venous plasma of the diseased and the normal kidney, PRA measurements can be regarded as proportional to plasma renin concentration in this condition.

Idiopathic edema

Idiopathic edema is a common disorder in younger women. In some cases, edema may be induced by abuse of diuretics for the purpose of weight reduction. In other cases, the pathogenesis of edema is obscure. Increased orthostatic fluid retention secondary to abnormal orthostatic venous 'pooling' and shifting of intravascular fluid into the interstitial space may play a role. Secondary hyperaldosteronism, if present, is usually due to diuretic treatment. Abnormalities in prolactin secretion are probably not a cause of idiopathic edema.

Einbauhemmung 14C-markierter Nucleoside in DNS und RNS von Ascites-Tumorzellen durch D-und L-Glycerinaldehyd

D-Glycerinaldehyd [10-2-m.] hemmt den Einbau von 14C-Thymidin in DNS von Asciteszellen unter aeroben und anaeroben Bedingungen um 80 bis 90 Prozent. Der Einbau von 14C-Uridin in RNS wird durch D-Glycerinaldehyd kaum gehemmt. L-Glycerinaldehyd [10-2-m.] hemmt den Thymidineinbau in DNS und den Uridineinbau in RNS und DNS unter aeroben Bedingungen nur schwach, bei Anaerobiose dagegen um zwei Zehnerpotenzen. Die Wirkung des D-Aldehyds auf den Thymidineinbau in DNS wird durch Auswaschen des Glycerinaldehyds kaum abgeschwächt.

In vivo activity of 11β-hydroxysteroid dehydrogenase type 1 in man: effects of prednisolone and chenodesoxycholic acid

The 11β-hydroxysteroid dehydrogenases (11β-HSDs) play a pivotal role in glucocorticoid (GC) action. 11β-HSD1 is a predominant reductase, activating GCs from inert metabolites, whereas 11β-HSD2 is a potent dehydrogenase inactivating GCs. Knowing the metabolic effects of GCs, a selective inhibition of 11β-HSD1 represents a potential target for therapy of impaired glucose tolerance, insulin insensitivity and central obesity. In vitro, 11β-HSD1 is selectively inhibited by chenodesoxycholic acid (CDCA) and upregulated under GC exposure. Therefore, we aimed to investigate the effects of CDCA and prednisolone on hepatic 11β-HSD1 activity in vivo by measuring 11-reduction of orally given cortisone (E) acetate to cortisol (F). CDCA or placebo was given to 5 male healthy volunteers within a randomised cross-over trial before and after oral administration of 12.5 mg E acetate at 8:00 h. For measurement of in vivo effects of GCs on 11β-HSD1 activity, hepatic reduction of 25 mg E acetate before and after treatment with prednisolone (30 mg for 6 days) was determined in 7 healthy males. Serum GC levels were determined using a fully automated liquid chromatographic system. CDCA had no effect on the activity of 11β-HSD1 in vivo. Prednisolone therapy leads to a marked rise in serum F concentrations and an elevated F/E serum ratio. This proves GC-induced activation of hepatic 11β-HSD1, which could not be extinguished by a parallel increase of IGF-1 under prednisolone. CDCA does not affect in vivo activity of 11β-HSD1 when given in therapeutic dosages. During GC treatment, increased hepatic activation of E to F may aggravate metabolic side effects of GCs such as seen in the metabolic syndrome.

Pharmacodynamics and pharmacokinetics of synthetic mineralocorticoids and glucocorticoids: receptor transactivation and prereceptor metabolism by 11beta-hydroxysteroid-dehydrogenases

Glucocorticoid (GC) and mineralocorticoid (MC) action in target tissues is determined by prereceptor metabolism by 11beta-hydroxysteroid-dehydrogenases (HSDs) and receptor transactivation. We characterized these parameters for steroids often used in clinical practice. HSD activity was examined in human liver (HSD1) and kidney microsomes (HSD2) and in CHO cells stably transfected with both enzymes. GC and MC transcriptional activity was tested by luciferase assay in CV-1 cells transfected with human GC or MC receptor expression vectors. The 11-hydroxy-group is necessary for GC and MC receptor transactivation. As HSD2 oxidizes 11-hydroxysteroids to inactive 11-dehydrosteroids, GC and MC activity in HSD2-expressing tissues (kidney, colon) is regulated by this enzyme. As 9alpha-fluorination (such as in 9alpha-fluorocortisol) decreases oxidation by HSD2 and increases both GC and MC receptor transactivation, this modification leads to optimal, but non-selective transactivation of both receptors. Increased GC receptor and decreased MC receptor transactivation leading to more selective GC activity is reached using the following substituents: 16beta-methyl (in betamethasone), 16alpha-methyl (in dexamethasone) and triangle up 1-dehydro-configuration (in prednisolone). Whereas the modifications in position 16 decrease oxidation by HSD2, the triangle up 1-dehydro-configuration increases HSD2-activity leading to an enhanced inactivation of prednisolone compared to all other steroids. 9alpha-fluorocortisol, the most frequently used substance for MC-substitution, seems to be the best choice of available steroids for this purpose. Whereas GC selectivity can be improved by hydrophobic substituents in position 16 and the triangle up 1-dehydro-configuration, maximal GC activity needs additional fluorination in position 9alpha (such as in dexamethasone). For GC therapy directed to HSD2-expressing organs, widely used prednisolone does not seem to be the optimal recommendation.

The role of progesterone metabolism and androgen synthesis in renal blood pressure regulation

11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2) plays a crucial role in converting hormonally active cortisol into inactive cortisone, conferring specificity onto the human mineralocorticoid receptor (MR). Progesterone binds with even higher affinity to the MR, but acts as an MR antagonist. How aldosterone is able to keep its function as predominant MR ligand in clinical situations with high progesterone concentrations, such as pregnancy, is not clear. We have shown in vitro that the human kidney possesses an effective enzyme system that metabolizes progesterone to inactive metabolites in a process similar to the inactivation of cortisol by 11beta-HSD2. In studies on patients with adrenal insufficiency, we have shown that the in vivo anti-mineralocorticoid activity of progesterone is diminished by inactivating metabolism of progesterone, local formation of the deoxycorticosterone mineralocorticoid from progesterone, and inhibition of 11beta-HSD2 by progesterone and its metabolites resulting in decreased inactivation of cortisol and hence increased MR binding by cortisol. The enzymes involved in progesterone metabolism are also responsible for the capability of the human kidney to convert pregnenolone to DHEA and androstenedione leading to the formation of active androgens, testosterone and 5alpha-DH-testosterone. Locally produced androgens might be responsible for the observed difference in blood pressure between men and women and higher susceptibility to hypertension in men.

Renal inactivation, mineralocorticoid generation, and 11beta-hydroxysteroid dehydrogenase inhibition ameliorate the antimineralocorticoid effect of progesterone in vivo

Progesterone (P) is a strong mineralocorticoid receptor (MR) antagonist in vitro. The high P concentrations seen in normal pregnancy only moderately increase renin and aldosterone concentrations. In previous in vitro studies we hypothesized that this may be explained by intrarenal conversion of P to less potent metabolites. To investigate the in vivo anti-MR potency of P, we performed an infusion study in patients with adrenal insufficiency (n = 8). They omitted 9alpha-fluorocortisol for 4 d and hydrocortisone for 0.5 d before a continuous iv infusion of aldosterone for 8.5 h, with an additional iv P infusion commenced at 4 h. During aldosterone infusions the initially elevated urinary sodium to potassium ratio decreased significantly. Despite the 1000-fold excess of P over aldosterone, the urinary sodium to potassium ratio and urinary sodium excretion increased only slightly after 3 h of P infusion. We detected inhibition of renal 11beta-hydroxysteroid dehydrogenase type 2 by P, thus giving cortisol/prednisolone access to the MR. Urinary and plasma concentrations of 17alpha-hydroxyprogesterone, a major metabolite of renal P metabolism, and those of serum androstenedione and deoxycorticosterone, a mineralocorticoid itself, increased significantly during P infusion. This supports the hypothesis of an effective protection of the MR from P by efficient extraadrenal downstream conversion of P.

The human kidney is a progesterone-metabolizing and androgen-producing organ

Progesterone (P) is a potent antagonist of the human mineralocorticoid receptor (MR) in vitro. We have previously demonstrated effective downstream metabolism of P in the kidney. This mechanism potentially protects the MR from P action. Here, we have investigated the expression and functional activity of steroidogenic enzymes in human kidney. RT-PCR analysis demonstrated the expression of 5 alpha-reductase type 1, 5 beta-reductase, aldo-keto-reductase (AKR) 1C1, AKR1C2, AKR1C3, 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) type 2, and 17 alpha-hydroxylase/17,20-lyase (P450c17). The presence of 3 beta-HSD type 2 and P450c17 indicated that conversion of pregnenolone to dehydroepiandrosterone (DHEA) and to androstenedione may take place effectively in kidney. To investigate this further, we incubated kidney subcellular fractions with radiolabeled pregnenolone. This resulted in efficient formation of DHEA from pregnenolone, indicating both 17 alpha-hydroxylase and 17,20-lyase activities exerted by P450c17. Radiolabeled DHEA was converted via androstenedione, androstenediol, and testosterone, indicating both 3 beta-HSD type 2 activity and 17 beta-HSD activity. In addition, the conversion of testosterone to 5 alpha-dihydrotestosterone was detectable, indicating 5 alpha-reductase activity. In conclusion, we verified the expression and functional activity of several enzymes involved in downstream metabolism of P and androgen synthesis in human kidney. These findings may be critical to the understanding of water balance during the menstrual cycle and pregnancy and of sex differences in hypertension.

Clinical diagnosis of hyper- and hypocortisolism

The clinical correlate of chronic hypercortisolism is Cushing's syndrome (CS). After exclusion of an iatrogenic cause (glucocorticoid administration), two reliable laboratory methods for establishing the diagnosis are (i) measurement of "free" (unmetabolised) cortisol in a 24-hour urine (UFC) sample and (ii) the low-dose (1 or 1.5 mg) dexamethasone (Dex) test. For the latter, Dex is taken orally at midnight, and plasma cortisol is measured at 8 a.m. In normals and in the absence of CS, the morning cortisol (200-650 nmol/L) is suppressed to <80 nmol/L. In endogenous CS of all causes, cortisol suppression by Dex is absent or incomplete. In patients with severe mental depression or stress, suppression may also be incomplete ("false-positives"). However, UFC is normal or only slight increased in the latter group, while it is always markedly increased in clinically apparent CS. In CS, UFC rises proportionally more than plasma cortisol because the cortisol binding plasma protein (transcortin) can bind only about 500 nmol/L cortisol. Protein-bound cortisol is not excreted by the kidney. After establishing the diagnosis CS, the differentiation between its pituitary (ca. 70%), adrenocortical (ca. 20%) or "ectopic" (ACTH production by non-pituitary tumours) (ca. 10%) origin is made by plasma ACTH measurement, a corticotropin releasing hormone injection test (with plasma ACTH/cortisol measurement) and a high-dose Dex (8 mg or more) suppression test. Chronic hypocorticolism can be primary (adrenal disease, Addison's disease) or secondary (pituitary or hypothalamic disorder). UFC measurement is not an established method for confirming hypocortisolism because most analytical methods are too unspecific and insensitive in the subnormal range. Low-normal or subnormal plasma cortisol plus elevated ACTH is the hallmark of Addison's disease. Injection of high doses of ACTH does not lead to a rise in plasma cortisol in these patients. A clearly subnormal cortisol plus low ACTH proves secondary hypocortisolism. Mild forms with low-normal plasma cortisol, however, are more difficult to prove. So-called "dynamic" tests stimulating the whole hypothalamo-pituitary-adrenal axis (insulin hypoglycemia test or metyrapone test) are necessary to confirm the diagnosis. Patients with hypocortisolism, depending on disease severity, must be treated permanently or only in stressful situations with hydrocortisone unless they may die after passing the clinical state of an "adrenal crisis".

Enhanced 11beta-hydroxysteroid dehydrogenase type 1 activity in stress adaptation in the guinea pig

The 11beta-hydroxysteroid dehydrogenases (11beta-HSDs) convert cortisol to its inactive metabolite cortisone and vice versa. 11beta-HSD type 1 (11beta-HSD-1) functions as a reductase in vivo, regulating intracellular cortisol levels and its access to the glucocorticoid receptor. In contrast, 11beta-HSD-2 only mediates oxidation of natural glucocorticoids, and protects the mineralocorticoid receptor from high cortisol concentrations. We investigated the in vivo and in vitro effects of ACTH on the recently characterized 11beta-HSDs in guinea pig liver and kidney. Tissue slices of untreated guinea pigs were incubated with (3)H-labelled cortisol or cortisone and ACTH(1-24) (10(-10) and 10(-9) mol/l). The 11beta-HSD activities in liver and kidney slices were not influenced by in vitro incubation with ACTH(1-24). In addition, guinea pigs were treated with ACTH(1-24) or saline injections s.c. for 3 days. Liver and kidney tissue slices of these animals were incubated with (3)H-labelled cortisol or cortisone. In vivo ACTH treatment significantly increased reductase and decreased oxidase activity in liver and kidney. Furthermore, 11beta-HSD-1 activity assessed by measurement of the urinary ratio of (tetrahydrocortisol (THF)+5alphaTHF)/(tetrahydrocortisone) was significantly increased after ACTH treatment compared with the control group. Plasma levels of cortisol, cortisone, progesterone, 17-hydroxyprogesterone and androstenedione increased significantly following in vivo ACTH treatment. The enhanced reductase activity of the hepatic and renal 11beta-HSD-1 is apparently caused by cortisol or other ACTH-dependent steroids rather than by ACTH itself. This may be an important fine regulation of the glucocorticoid tonus for stress adaptation in every organ, e.g. enhanced gluconeogenesis in liver.

Antimineralocorticoid activity of a novel oral contraceptive containing drospirenone, a unique progestogen resembling natural progesterone

Sex hormones are known to interfere with the renin-angiotensin-aldosterone system (RAAS) in two ways. First, estrogens strongly stimulate the production of renin substrate (angiotensinogen), leading to increased levels of angiotensin and aldosterone, and sodium retention. Second, progesterone is a potent aldosterone antagonist, which acts on the mineralocorticoid receptor to prevent sodium retention. In combined oral contraceptives, progestogens devoid of antimineralocorticoid and antiandrogenic activity are unable to counteract the sodium-retaining effect of the ethinylestradiol component. As a consequence, these preparations may increase fluid retention, and promote related symptoms such as edema and body weight. Drospirenone is a new progestogen with antimineralocorticoid and antiandrogenic activity. The relationship between the progestogenie and antimincralocorticoid potency of drospirenone is similar to that of endogenous progesterone. At a dosage that suppresses ovulation, drospirenone induces mild natriuresis, which is followed by compensatory stimulation of the RAAS (comparable to a low sodium diet). An oral contraceptive containing 3 mg drospirenone and 30 microg ethinylestradiol. (Yasmin, Schering AG, Berlin, Germany) provides reliable contraception and, due to a lack of sodium retention, may counteract cyclical weight gain and other symptoms related to estrogen-induced fluid retention.

Expression of the progesterone receptor and progesterone- metabolising enzymes in the female and male human kidney

Due to high binding affinity of progesterone to the human mineralocorticoid receptor (hMR), progesterone competes with the natural ligand aldosterone. In order to analyse how homeostasis can be maintained by mineralocorticoid function of aldosterone at the MR, especially in the presence of elevated progesterone concentrations during the luteal phase and pregnancy, we investigated protective mechanisms such as the decrease of free progesterone by additional binding sites and progesterone metabolism in renal cells. As a prerequisite for sequestration of progesterone by binding to the human progesterone receptor (hPR) we demonstrated the existence of hPR expression in female and male kidney cortex and medulla at the level of transcription and translation. We identified hPR RNA by sequencing the RT-PCR product and characterised the receptor by ligand binding and scatchard plot analysis. The localisation of renal hPR was shown predominantly in individual epithelial cells of distal tubules by immunohistology, and the isoform hPR-B was detected by Western blot analysis. As a precondition for renal progesterone metabolism, we investigated the expression of steroid-metabolising enzymes for conversion of progesterone to metabolites with lower affinity to the hMR. We identified the enzyme 17alpha-hydroxylase for renal 17alpha-hydroxylation of progesterone. For 20alpha-reduction, different hydroxysteroid dehydrogenases (HSDs) such as 20alpha-HSD, 17beta-HSD type 5 (3alpha-HSD type 2) and 3alpha-HSD type 3 were found. Further, we detected the expression of 3beta-HSD type 2 for 3beta-reduction, 5alpha-reductase (Red) type 1 for 5alpha-reduction, and 5beta-Red for 5beta-reduction of progesterone in the human kidney. Therefore metabolism of progesterone and/or binding to hPR could reduce competition with aldosterone at the MR and enable the mineralocorticoid function.

Agonistic and antagonistic properties of progesterone metabolites at the human mineralocorticoid receptor

OBJECTIVE

Progesterone binds to the human mineralocorticoid receptor (hMR) with nearly the same affinity as do aldosterone and cortisol, but confers only low agonistic activity. It is still unclear how aldosterone can act as a mineralocorticoid in situations with high progesterone concentrations, e.g. pregnancy. One mechanism could be conversion of progesterone to inactive compounds in hMR target tissues.

DESIGN

We analyzed the agonist and antagonist activities of 16 progesterone metabolites by their binding characteristics for hMR as well as functional studies assessing transactivation.

METHODS

We studied binding affinity using hMR expressed in a T7-coupled rabbit reticulocyte lysate system. We used co-transfection of an hMR expression vector together with a luciferase reporter gene in CV-1 cells to investigate agonistic and antagonistic properties.

RESULTS

Progesterone and 11beta-OH-progesterone (11beta-OH-P) showed a slightly higher binding affinity than cortisol, deoxycorticosterone and aldosterone. 20alpha-dihydro(DH)-P, 5alpha-DH-P and 17alpha-OH-P had a 3- to 10-fold lower binding potency. All other progesterone metabolites showed a weak affinity for hMR. 20alpha-DH-P exhibited the strongest agonistic potency among the metabolites tested, reaching 11.5% of aldosterone transactivation. The agonistic activity of 11beta-OH-P, 11alpha-OH-P and 17alpha-OH-P was 9, 5.1 and 4.1% respectively. At a concentration of 100 nmol/l, progesterone, 17alpha-OH-P and 20alpha-DH-P inhibit nearly 75, 40 and 35% of the transactivation by aldosterone respectively. All other progesterone metabolites tested demonstrate weaker affinity, and agonistic and antagonistic potency.

CONCLUSIONS

The binding affinity for hMR and the agonistic and antagonistic activity diminish with increasing reduction of the progesterone molecule at C20, C17 and at ring A. We assume that progesterone metabolism to these compounds is a possible protective mechanism for hMR. 17alpha-OH-P is a strong hMR antagonist and could exacerbate mineralocorticoid deficiency in patients with congenital adrenal hyperplasia.

Differential diagnosis of polyuric/polydipsic syndromes with the aid of urinary vasopressin measurement in adults

OBJECTIVE

A water deprivation test or a hypertonic saline infusion test with the measurement of plasma osmolality and plasma vasopressin are the gold standard tests in the differential diagnosis of polyuric syndromes. Because commercially available vasopressin kits are too insensitive for this approach, and the concentration of vasopressin in urine is much higher than in plasma, urinary vasopressin measurements may be an alternative to the more difficult plasma vasopressin measurement.

DESIGN

The diagnostic value of the measurement of urinary vasopressin with a rather insensitive commercially available vasopressin kit was compared with plasma vasopressin measurement by a highly sensitive radioimmunoassay (RIA).

PATIENTS AND METHODS

Thirteen normal subjects and 27 patients with polyuria/polydipsia were examined by an 8-h fluid deprivation test. In all blood samples (0800 h, 1200 h, 1400 h and 1600 h) and in all urine collections (2-hourly fractions), osmolality as well as vasopressin were measured.

RESULTS

Using plasma vasopressin measurement with a highly sensitive RIA as gold standard test, nine patients were classified as having primary polydipsia, whereas 18 had partial or complete cranial diabetes insipidus. Whereas the substitution of plasma vasopressin measurement by urinary vasopressin measurement alone did not provide 100% separation between both groups, the product of urinary vasopressin and urinary osmolality related to plasma osmolality completely separated the patients with primary polydipsia from those with diabetes insipidus. Urinary measurement of vasopressin and osmolality alone, which was recommended as a noninvasive diagnostic procedure in children, was too insensitive for exact differential diagnosis in our adult patients.

CONCLUSIONS

The simultaneous measurement of plasma vasopressin and plasma osmolality in a dehydration test is the most powerful diagnostic tool in the differential diagnosis of polyuria/polydipsia. However, if highly sensitive assays for plasma vasopressin measurements are not available, the measurement of urinary vasopressin with commercially available, less sensitive RIAs may be a diagnostic alternative, which showed nearly the same sensitivity as plasma vasopressin measurement in our study population.

Therapeutic strategies in adrenal insufficiency

Severe chronic adrenal insufficiency (primary or secondary) is a potentially lethal disorder, unless the patient is regularly substituted with glucocorticoids, usually with hydrocortisone (15-25 mg/day) and with 9 alpha-fluor-hydrocortisone (0.05-0.2 mg/day) in addition in patients with the primary adrenal disorder (Addison's disease). In stressful situations and in febrile disorders, the glucocorticoid dosage must be increased prophylactically in order to prevent an "adrenal crisis". Most women with adrenal insufficiency will profit from the additional substitution of dehydroepiandrosterone (DHEA) with regard to well-being and sexual function. A patient with acute adrenal insufficiency will die if the diagnosis is missed and high-dose glucocorticoid treatment is not instituted immediately. Acute adrenal insufficiency developing de novo in an intensive care patient (e.g. from adrenal hemorrhage or adrenal vein thrombosis) is a most challenging diagnosis. In these patients, however, survival not only depends on glucocorticoid substitution but also on the underlying disease.

Clinical implications of glucocorticoid metabolism by 11beta-hydroxysteroid dehydrogenases in target tissues

11beta-Hydroxysteroid dehydrogenases (11beta-HSD) are microsomal enzymes that catalyze the conversion of active glucocorticoids (GC) to their inactive 11-dehydro products and vice versa. Two isoenzymes of 11beta-HSD have been characterized and cloned in human tissues. The tissue-specific metabolism of GC by these enzymes is important for mineralocorticoid (MC) and GC receptor occupancy and seems to play a crucial role in the pathogenesis of diseases such as apparent MC excess syndrome, and may play roles in hypertension, obesity and impaired hepatic glucose homeostasis. This article reviews the literature and examines the role and importance of 11beta-HSD in humans.

Enzyme-mediated protection of the mineralocorticoid receptor against progesterone in the human kidney

Progesterone (P) is a mineralocorticoid (MC)-antagonist in vitro. During pregnancy, plasma P concentrations exceed aldosterone concentrations at least 50-fold, but plasma aldosterone increases only 4-8-fold in a compensatory manner. Since the in vivo anti-MC activity of P seems to be only moderate, we hypothesized that P is metabolized by enzymes of MC target tissue similar to the way cortisol is metabolized by 11beta-hydroxysteroid dehydrogenase (11beta-HSD) type 2 in order to protect the MC receptor. We, therefore, examined P metabolism using 4-(14)C-P in subcellular fractions of human postmenopausal and male kidneys, and in homogenates of one premenopausal kidney. We found that P is converted effectively, even at high P concentrations (10(-6) mol/l), to various metabolites: 20alpha-dihydro(DH)-P; 17alpha-OH-P; 17alpha-OH,20alpha-DH-P; 5alpha-DH-P; 3beta,5alpha-tetrahydro(TH)-P; and 20alpha-DH,5alpha-DH-P. Homogenates of premenopausal kidney also showed conversion to 3alpha- and 5beta-reduced P metabolites. These results confirm the existence of an efficient renal enzyme system as a possible mechanism of an enzyme-mediated MC receptor selectivity.

Drospirenone--a new progestogen with antimineralocorticoid activity, resembling natural progesterone

In the second half of a normal menstrual cycle, progesterone levels rise. Progesterone binds to its specific receptor, but also to the mineralocorticoid receptor; thus progesterone acts as a mineralocorticoid antagonist. For this reason, natriuresis is slightly enhanced in the luteal phase, and, as a reflection of the negative sodium balance, plasma renin and aldosterone rise by 20-50%. This rise is of a compensatory nature, and prevents further sodium losses. All conventional synthetic progestogens, whether they are derivatives of 17alpha-hydroxyprogesterone or 19-nortestosterone, lack the antimineralocorticoid effect of natural progesterone. Ethinylestradiol, as the estrogenic component of combined oral contraceptives, is a sodium-retaining drug. This effect is mainly due to a significant increase of the hepatic synthesis of renin substrate (angiotensinogen). Even with low-dose oral contraceptives, systolic and diastolic blood pressure may be raised in susceptible individuals. Drospirenone is a new progestogen, derived from 17alpha-spirolactone, and the relationship between its progestogenic and its antimineralocorticoid potency is almost identical to that of natural progesterone. In an early preclinical study in 12 normal young women, it was found that the oral administration of 2 mg drospirenone for 6 days led to a cumulative sodium loss of 84 mmol and a significant rise in plasma renin and aldosterone, compared with placebo. In a second experiment, it was found that 2 mg drospirenone given from cycle days 5 to 25 to six regularly menstruating women suppressed ovulation and led to a slight natriuresis without a change in blood pressure, while renin and aldosterone levels slightly increased. The natriuresis and the increase in renin and aldosterone levels did not occur in six other women who received 1 mg cyproterone acetate (a progestogen with antiandrogenic properties), instead of drospirenone. Consequently, an oral contraceptive was designed containing 30 microg ethinylestradiol and 3 mg drospirenone (Yasmin, Schering AG, Berlin, Germany) in the hope of developing a contraceptive that might prevent the sodium retention brought about by the effect of ethinylestradiol. In a 6-month study involving 20 regularly menstruating women, it was shown that the addition of drospirenone to ethinylestradiol did indeed prevent the small rise in body weight and blood pressure observed in some women taking a conventional oral contraceptive. In all studies conducted so far with Yasmin, cycle control and tolerability have been found to be good. In conclusion, Yasmin may become an especially well-tolerated combined oral contraceptive, due to the striking similarity between its progestogenic component drospirenone and progesterone.

11Beta-hydroxysteroid-dehydrogenase isoforms: tissue distribution and implications for clinical medicine

11Beta-hydroxylation is essential for glucocorticoid and mineralocorticoid activity of a steroid. The enzyme catalyzing this reaction is termed 11beta-hydroxysteroid-dehydrogenase (11beta-HSD). Two isoenzymes of 11beta-HSD have been characterized in human tissues. Whereas 11beta-HSD-I works mainly as a reductase, 11beta-HSD-II only functions as an oxidizing (inactivating) enzyme for physiological glucocorticoids. Thus, the tissue distribution of both enzymes plays a crucial role for the specific glucocorticoid status of an organ. This review summarizes our knowledge of tissue distribution of both 11beta-HSD isoenzymes, their physiological function and pathophysiological role in certain clinical abnormalities, and their relevance to the metabolism of synthetic glucocorticoid and mineralocorticoid compounds.

Severely impaired baroreflex-buffering in patients with monogenic hypertension and neurovascular contact

BACKGROUND

We identified a family with a monogenic syndrome of hypertension, brachydactyly, and neurovascular contact of the brain stem. Neurovascular contact of the ventrolateral medulla may lead to arterial hypertension by interfering with baroreflex function.

METHODS AND RESULTS

In 5 patients with monogenic hypertension (18 to 34 years old), we conducted detailed autonomic function tests. Blood pressure during complete ganglionic blockade was 134+/-4.9/82+/-4.1 mm Hg and 90+/-6/49+/-2.4 mm Hg in patients and in control subjects, respectively. During ganglionic blockade, plasma vasopressin concentration increased 24-fold in control subjects and <2-fold in patients. In patients, cold pressor testing, hand-grip testing, and upright posture all increased blood pressure excessively. In contrast, muscle sympathetic nerve activity was not increased at rest or during cold pressor testing. The phenylephrine dose that increased systolic blood pressure 12.5 mm Hg was 8.0+/-2.0 microg in patients and 135+/-35 microg in control subjects before ganglionic blockade and 5.4+/-0.4 microg in patients and 13+/-4.8 microg in control subjects during ganglionic blockade.

CONCLUSIONS

In patients with monogenic hypertension and neurovascular contact, basal blood pressure was increased even during sympathetic and parasympathetic nerve traffic interruption. However, sympathetic stimuli caused an excessive increase in blood pressure. This excessive response cannot be explained by increased sympathetic nerve traffic or increased vascular sensitivity. Instead, we suggest that baroreflex buffering and baroreflex-mediated vasopressin release are severely impaired.

Dose-response relationship between plasma ACTH and serum cortisol in the insulin-hypoglycaemia test in 25 healthy subjects and 109 patients with pituitary disease

OBJECTIVE

The insulin hypoglycaemia test (IHT) is believed to be the most reliable test for evaluating the entire hypothalamo-pituitary-adrenal (HPA) axis. The lower limit for the normal peak serum cortisol response has been reported to be between 500 and 580 nmol/l. Reference levels for a normal plasma ACTH response have not been reported recently.

DESIGN AND PATIENTS

We performed the IHT in 25 healthy subjects and in 109 patients with proven or suspected pituitary disorders with serial measurements of serum or plasma cortisol and of plasma ACTH, in order to establish reference levels and to study the dose-response relationship between ACTH and cortisol in this test. In most patients, other pituitary hormonal axes were evaluated in addition.

RESULTS

With the cortisol kit from Diagnostic Products Corporation (DPC), serum cortisol was about 13% lower than plasma (EDTA) levels with an excellent correlation between serum and plasma (r = 0.976; P<0.001). In the normals, the lower limit of the cortisol response (mean cortisol peak level minus 2 SD.) was 570 nmol/l for plasma and 500 nmol/l (calculated) for serum, while the lower limit of the ACTH response was 17.6 pmol/l (80 ng/l). In normals, the cortisol response was independent of the magnitude of the ACTH response. Seventeen out of 30 patients with ACTH responses to levels < 8.8 pmol/l (< 40 ng/l) had subnormal cortisol responses. However, 38 of the patients with pituitary disease had normal cortisol responses in spite of subnormal ACTH responses (group 2), while 47 patients had completely normal IHT results (group 1). Patients in group 2 had more often additional pituitary hormone deficiencies than those of group 1. The dose-response relationship between ACTH and cortisol in the patients resembled a dose-response curve that had been set up previously in normal subjects who received incremental doses of subcutaneous human ACTH (1-39).

CONCLUSIONS

The normal increment of plasma ACTH in the IHT is greater than necessary for stimulating serum cortisol to levels > 500 nmol/l. Patients with a subnormal ACTH but normal cortisol response in the IHT have a decreased ACTH secretory reserve. It is unlikely that they are at increased risk of developing an adrenal crisis perioperatively or in other stressful situations unless pituitary function deteriorates. The ACTH-cortisol relationship in the IHT performed in patients with pituitary disease shows no sharp dividing line between normality and disease, and whether a patient needs permanent glucocorticoid substitution is a discretionary decision.

Primary hyperaldosteronism without suppressed renin due to secondary hypertensive kidney damage

Primary hyperaldosteronism is characterized by high plasma and urinary aldosterone and suppressed PRA. Renin suppression is due to aldosterone-dependent sodium retention and mild extracellular volume expansion. We observed three patients with primary hyperaldosteronism, severe refractory hypertension, and normal to high normal PRA levels whose aldosterone/renin ratios were still elevated because of disproportionately high aldosterone levels. All available medical data on the patients as well as publications on the aldosterone/renin relationship in primary hyperaldosteronism were reviewed to explain the unusual findings. In one patient, histologically proven renal arteriolosclerosis was the probable cause of the escape of PRA from suppression by an aldosterone-producing adenoma. In the other two patients, hypertensive kidney damage due to primary hyperaldosteronism was the most likely explanation for the inappropriately high PRA, as in patient 1. All patients had high normal or slightly elevated serum creatinine levels and responded to 200 mg spironolactone/day with increased serum creatinine and hyperkalemia. Hyperkalemia was probably due to a decreased filtered load of sodium and a spironolactone-induced decrease in mineralocorticoid function. Two patients were cured of hyperaldosteronism by unilateral adrenalectomy but still need some antihypertensive therapy, whereas one patient has probable bilateral adrenal disease, with normal blood pressure on a low dose of spironolactone. In patients with severe hypertension due to primary hyperaldosteronism, PRA can escape suppression if hypertensive kidney damage supervenes. An increased aldosterone/PRA ratio is still useful in screening for primary hyperaldosteronism. These patients may respond to spironolactone therapy with a strong increase in serum creatinine and potassium. Early specific treatment of primary hyperaldosteronism is therefore indicated, and even a patient with advanced hypertension will profit from adrenalectomy or cautious spironolactone treatment.

Effect of an oral contraceptive containing drospirenone on the renin-angiotensin-aldosterone system in healthy female volunteers

Drospirenone is a new synthetic progestogen with both progestational, antimineralocorticoid and antiandrogenic properties. In combination with ethinylestradiol, it is being developed as an oral contraceptive which will contain 30 micrograms ethinylestradiol and 3 mg drospirenone (Yasmin, Schering AG, Germany). The effects of drospirenone alone, and in combination with ethinylestradiol, upon the renin-angiotensin-aldosterone system (RAAS) have been evaluated in healthy female volunteers. RAAS activity was assessed by measurement of plasma renin substrate (PRS) concentration (otherwise known as angiotensinogen), plasma renin activity (PRA), and plasma aldosterone (P-Aldo) concentration. An antimineralocorticoid effect was observed when volunteers received drospirenone alone at doses in the range 0.5-3.0 mg/day for one cycle. The effect was dose-dependent for P-Aldo but was not dose-dependent for PRA. When ethinylestradiol (30 micrograms) was combined with either 2 mg or 3 mg drospirenone and given to volunteers for three cycles, an increase in PRS was observed with both preparations, which was indicative of estrogenic stimulation, and increases in PRA and P-Aldo were shown which were indicative of an antimineralocorticoid effect of drospirenone. Increases in PRA and P-Aldo were significantly higher with the preparation containing 3 mg drospirenone in cycle 1 but not in cycle 3. The effect of the preparation containing 30 micrograms ethinylestradiol/3 mg drospirenone upon RAS activity was also compared with that of a commercially available preparation also containing 30 micrograms ethinylestradiol but combined with 150 micrograms desogestrel (Marvelon). Over a period of 13 cycles, increases in PRS were seen with both treatments, the effect being slightly more pronounced with 30 micrograms ethinylestradiol/150 micrograms desogestrel. A markedly greater increase in PRA was seen following treatment with 30 micrograms ethinylestradiol/3 mg drospirenone, and, in cycle 3, this difference was statistically significant. In contrast, P-Aldo was increased markedly with 30 micrograms ethinylestradiol/3 mg drospirenone in all measured cycles, whereas, in the 30 micrograms ethinylestradiol/150 micrograms desogestrel group, changes were minimal. The increases in PRA and P-Aldo are interpreted as endogenous counter-regulation against the antimineralocorticoid activity of drospirenone. PRS increases under all combinations are an expression of estrogenic stimulation. Measurement of body weight and blood pressure in the studies with combined ethinylestradiol and drospirenone revealed that drospirenone was associated with either stable body weight or with a slight loss in body weight, while blood pressure remained largely unchanged. Overall, the results indicate that 30 micrograms ethinylestradiol/3 mg drospirenone has a distinct antimineralocorticoid effect.

In the search for specific inhibitors of human 11beta-hydroxysteroid-dehydrogenases (11beta-HSDs): chenodeoxycholic acid selectively inhibits 11beta-HSD-I

OBJECTIVE

Selective inhibitors of 11beta-hydroxysteroid-dehydrogenase type I may be of therapeutical interest for two reasons: i) 9alpha-Fluorinated 11-dehydrosteroids like 11-dehydro-dexamethasone (DH-D) are rapidly activated by human kidney 11beta-hydroxysteroid-dehydrogenase type II (11beta-HSD-II) to dexamethasone (D). If the same reaction by hepatic 11beta-HSD-I could be selectively inhibited, DH-D could be used for selective renal immunosuppressive therapy. ii) Reduction of cortisone to cortisol in the liver may increase insulin resistance in type 2 diabetes mellitus, and inhibition of the enzyme may lead to a decrease in gluconeogenesis. Therefore, we characterized the metabolism of DH-D by human hepatic 11beta-HSD-I and tried to find a selective inhibitor of this isoenzyme.

METHODS

For kinetic analysis of 11beta-HSD-I, we used microsomes prepared from unaffected parts of liver segments, resected because of hepatocarcinoma or metastatic disease. For inhibition experiments, we also tested 11beta-HSD-II activity with human kidney cortex microsomes. The inhibitory potency of several compounds was evaluated for oxidation and reduction in concentrations from 10(-9) to 10(-5)mol/l.

RESULTS

Whereas D was not oxidized by human liver microsomes at all, cortisol was oxidized to cortisone with a maximum velocity (V(max)) of 95pmol/mg per min. The reduction of DH-D to D (V(max)=742pmol/mg per min, Michaelis--Menten constant (K(m))=1.6 micromol/l) was faster than that of cortisone to cortisol (V(max)=187pmol/mg per min). All reactions tested in liver microsomes showed the characteristics of 11beta-HSD-I: K(m) values in the micromolar range, preferred cosubstrate NADP(H), no product inhibition. Of the substances tested for inhibition of 11beta-HSD-I and -II, chenodeoxycholic acid was the only one that selectively inhibited 11beta-HSD-I (IC(50) for reduction: 2.8x10(-6)mol/l, IC(50) for oxidation: 4.4x10(-6)mol/l), whereas ketoconazole preferentially inhibited oxidation and reduction reactions catalyzed by 11beta-HSD-II. Metyrapone, which is reduced to metyrapol by hepatic 11beta-HSD-I, inhibited steroid reductase activity of 11beta-HSD-I and -II and oxidative activity of 11beta-HSD-II. These findings can be explained by substrate competition for reductase reactions and by product inhibition of the oxidation, which is a well-known characteristic of 11beta-HSD-II.

CONCLUSIONS

Our in vitro results may offer a new concept for renal glucocorticoid targeting. Oral administration of small amounts of DH-D (low substrate affinity for 11beta-HSD-I) in combination with chenodeoxycholic acid (selective inhibition of 11beta-HSD-I) may prevent hepatic first pass reduction of DH-D, thus allowing selective activation of DH-D to D by the high affinity 11beta-HSD-II in the kidney. Moreover, selective inhibitors of the hepatic 11beta-HSD-I, like chenodeoxycholic acid, may become useful in the therapy of patients with hepatic insulin resistance including diabetes mellitus type II, because cortisol enhances gluconeogenesis.

Progesterone metabolism in the human kidney and inhibition of 11beta-hydroxysteroid dehydrogenase type 2 by progesterone and its metabolites

Progesterone binds with high affinity to the mineralocorticoid (MC) receptor, but confers only very low agonistic MC activity. Therefore, progesterone is a potent MC antagonist in vitro. Although progesterone reaches up to 100 times higher plasma levels in late pregnancy than aldosterone, the in vivo MC antagonistic effect of progesterone seems to be relatively weak. One explanation for this phenomenon could be local metabolism of progesterone in the human kidney, similar to the inactivation of cortisol to cortisone by the 11beta-hydroxysteroid dehydrogenase (11beta-HSD) type 2. We studied the metabolism of progesterone in the human kidney in vitro and found reduction to 20alpha-dihydro (DH)-progesterone as the main metabolite. Ring-A reduction to 5alpha-DH-progesterone, 20alpha-DH-5alpha-DH-progesterone, and 3beta,5alpha-tetrahydro (TH)-progesterone was also documented. We further showed for the first time that 17-hydroxylation of progesterone (17alpha-OH-progesterone, 17alpha-OH, 20alpha-DH-progesterone), normally localized in the adrenals and the gonads, occurs in the human adult kidney. We found no formation of deoxycorticosterone from progesterone in the human adult kidney. Using human kidney cortex microsomes, we tested the inhibitory potency of progesterone and its metabolites on the 11beta-HSD type 2. The most potent inhibitor was progesterone itself (IC50 = 4.8 x 10(-8) mol/L), followed by 5alpha-DH-progesterone (IC50 = 2.4 x 10(-7) mol/L), 20alpha-DH-progesterone, 3beta,5alpha-TH-progesterone, 17alpha-OH-progesterone, and 20alpha-DH-5alpha-DH-progesterone (IC50 between 7.7 x 10(-7) mol/L and 1.3 x 10(-6) mol/L). The least potent inhibitor was 17alpha-OH,20alpha-DH-progesterone. In addition to progesterone metabolism by the kidney, the inhibition of 11beta-HSD type 2 by progesterone and its metabolites could be a second explanation for the weak MC-antagonist activity of progesterone in vivo. Inhibition of 11beta-HSD type 2 leads to an increase of intracellular cortisol in a way that the local equilibrium between the MC agonist cortisol and the antagonist progesterone is shifted to the agonist side.

Torsemide inhibits aldosterone secretion in vitro

Torsemide inhibited aldosterone secretion by adrenal cells from rats, cows, and guinea pigs stimulated in vitro by potassium, angiotensin, dibutyryl cyclic AMP, ACTH, or corticosterone. Inhibitory concentrations for adrenal cells (micromolar) were comparable with those reported to inhibit ion transport in isolated renal tubules. Inhibition of aldosterone secretion could reduce kaliuresis, and that may explain why torsemide causes less kaliuresis than other diuretics.

Metabolism of synthetic corticosteroids by 11 beta-hydroxysteroid-dehydrogenases in man

The presence of an 11 beta-hydroxyl group is essential for the anti-inflammatory and immunosuppressive effects of glucocorticoids. Interconversion of the 11 beta-hydroxyl into the corresponding 11 beta-keto group and vice versa by 11 beta-hydroxysteroid-dehydrogenase (11 beta-HSD) may thus play a pivotal role in the efficacy of these steroids. Therefore, we have compared the metabolism of the endogenous glucocorticoid cortisol (F) with that of synthetic 9 alpha-fluorinated steroids by 11 beta-HSDs in humans in vivo and in vitro. Whereas 30% of the free steroids in urine after oral administration of 5 mg of F is F itself and 70% the inactive keto-product cortisone (E), the urinary excretion of an identical dose of oral 9 alpha-fluorocortisol (9 alpha FF) is 90% 9 alpha FF and 10% inactive 9 alpha-fluorocortisone (9 alpha FE). Kidney slices similarly convert F much faster to E than 9 alpha FF to 9 alpha FE; conversely, renal 11 beta-reduction of 9 alpha FE to 9 alpha FF is much more effective than that of E to F. Kinetic analyses in human kidney cortex microsomes prove that the preference of fluorinated steroids for reduction in human kidney slices is catalyzed by 11 beta-HSD type II: the NADH-dependent conversion of 11-dehydro-dexamethasone (DH-D), another fluorinated steroid, to dexamethasone (D) is very effective (high affinity, high Vmax), whereas reduction of E to F is very slow. In human liver microsomes (11 beta-HSD type I), nonfluorinated (E) and fluorinated 11-dehydrosteroids (DH-D) are both reduced to their corresponding active 11-hydroxyderivatives but with a Michaelis-Menten constant about 20-fold higher than for kidney microsomes (11 beta-HSD-II). Our results suggest that the decreased renal 11 beta-oxidation of 9 alpha-fluorinated steroids may offer pharmacokinetic advantages for renal immunosuppression. Furthermore, administration of fluorinated 11-dehydrosteroids is a new and exciting idea in glucocorticoid therapy in that small amounts of oral DH-D may pass the liver largely unmetabolized (11 beta-HSD-I has low affinity for such steroids) and may then be activated to D by high-affinity 11 beta-HSD-II, thus allowing selective immunosuppression in organs expressing 11 beta-HSD-II (kidney and colon).

Comparison of low and high dose corticotropin stimulation tests in patients with pituitary disease

Tetracosactin [corticotropin-(1-24)] is used for clinical testing of adrenocortical responsiveness. The usual dose [high dose test (HDT)] is 250 micrograms. With this test, patients with mild secondary adrenal insufficiency are usually not identified, thus putting them at risk of an adrenal crisis in stressful situations. It was recently reported that a tetracosactin test with approximately 1 micrograms [low dose test (LDT)] identifies patients with mild forms of pituitary-adrenal insufficiency. We performed both the HDT and the LDT in 35 control subjects and in 44 patients with pituitary disease, mostly pituitary tumors. In these patients, more sensitive reference tests for evaluating the pituitary-adrenal axis (insulin-induced hypoglycemia, metyrapone, and CRH tests) were also performed. In the HDT, plasma cortisol was measured 30 and 60 min after tetracosactin injection; in the LDT (0.5 microgram/m2 body surface area), plasma cortisol was measured 20, 30, 40, 50, and 60 min postinjection. In 6 control subjects, tetracosactin plasma levels were also measured after injection. In the HDT, the correlation between 30 and 60 min cortisol levels was extremely high (r = 0.991; P < 0.0001), but the correlation of the LDT with the HDT at 30 min was also highly significant (r = 0.948; P < 0.0001). The lower normal limit of cortisol responses (means of controls minus 2 SD) at 30 min was lower in the LDT by 3.1 micrograms/dL (85 nmol/L) than in the HDT. Compared with the reference tests, the diagnostic sensitivities of the HDT and the LDT were almost identical. Both tests identified patients with moderately to severely pathological insulin and metyrapone tests, but not those with slightly pathological reference tests. In the HDT, plasma tetracosactin rose to more than 60,000 pg/mL shortly after injection. In the LDT, it rose to 1,900 pg/mL. Both concentrations stimulate cortisol (supra-) maximally. Together, these data show that in pituitary disorders the results of the LDT and the HDT are almost identical. Plasma tetracosactin levels in the LDT still rise to levels that maximally stimulate the adrenal. Tetracosactin testing with low or high doses cannot generally replace the more expensive and cumbersome insulin or metyrapone tests.

A very high dose dexamethasone suppression test for differential diagnosis of Cushing's syndrome

OBJECTIVE

The high-dose dexamethasone (dex) suppression test of cortisol secretion (8 x 2 mg dex over two days or 8 mg overnight) is a mainstay in the differential diagnosis of Cushing's syndrome (CS). In some patients with pituitary Cushing's disease (CD), however, plasma cortisol is not suppressed to < 50% of control by 8 mg of dex. We therefore hypothesized that a higher dose of dex might produce more effective suppression of cortisol secretion in CD.

DESIGN AND SUBJECTS

We routinely tested the diagnostic efficacy of a very high dose of dex (32 mg, i.e. 4 x 8 mg in 24 hours) in comparison with the 8 mg overnight dex test in a population of patients with CD, in which an unusually high percentage was refractory to 8 mg dex. End points were the suppression of plasma cortisol, plasma ACTH and urinary free cortisol (UFC) to < 50% of control. Corticotrophin releasing hormone (human CRH) tests were also performed.

RESULTS

Eleven out of 26 (11/26) patients with CD (42%), among them six with pituitary macro-adenomas, failed to show suppression of plasma cortisol after 8 mg dex. Five out of 19 patients (26%) with CD failed to suppress after 32 mg dex. Only 3/19 (16%) failed to suppress UFC after 32 mg dex. In nonpituitary CS (n = 11), only one patient with macro-nodular adrenal hyperplasia showed significant suppression of plasma cortisol, but not UFC, after 32 mg dex. ACTH suppression after 8 or 32 mg dex was often less pronounced than that of cortisol and was of no diagnostic value. Cortisol stimulation by > or = 23% after hCRH injection differentiated 100% of patients with CD from other forms of CS.

CONCLUSION

In this series, the hCRH test was the most reliable test for the differential diagnosis of Cushing's syndrome. The 32 mg dexamethasone test with measurement of urinary free cortisol was clearly superior to the 8 mg test and to other aspects of the very high dose dexamethasone test. It can be recommended for 'non-suppressible' patients with ACTH-dependent Cushing's syndrome and can be performed on outpatients.

[Mineralocorticoid-induced hypertension]

Several important advances have been made in the pathogenesis of mineralocorticoid induced hypertension. A hybrid gene was found to be responsible for glucocorticoid remediable hypertension. This extra gene contains fragments of 11-beta-hydroxylase and aldosterone synthase. The hybrid gene is the result of an unequal crossing-over of the two genes located in close proximity on chromosome 8, and leads to the production of aldosterone and the hybrid steroids 18-hydroxycortisol and 18-oxocortisol. These hybrid steroids are also detected in patients with aldosterone producing adenoma but not in patients with hyperaldosteronism due to bilateral adrenal hyperplasia. In Apparent "Mineralocorticoid Excess", inherited as an autosomal recessive disorder, an increased ratio of urinary cortisol metabolite to cortisone is diagnostic. The syndrome is due to a deficiency of the renal enzyme 11-beta-hydroxysteroid dehydrogenase type II, which protects the mineralocorticoid receptor against cortisol that binds to the mineralocorticoid receptor like aldosterone. Liddle's syndrome is a rare entity and due to a constitute activation of an aldosterone dependent protein which triggers the amiloride sensitive sodium channel in the kidney. This results in hypokalemic hypertension with suppressed aldosterone and renin levels.

Evidence for isoforms of 11 beta-hydroxysteroid dehydrogenase in the liver and kidney of the guinea pig

In the human and in rodents like the rat and mouse, the liver enzyme 11 beta-hydroxysteroid dehydrogenase type I (11 beta-HSD-I) is a functional oxidoreductase preferring NADP+/NADPH as cosubstrate, while the renal isoenzyme (11 beta-HSD-II) prefers NAD+ as cosubstrate, and seems to be a pure oxidase and protects the tubular, mineralocorticoid (MC) receptor from occupancy by cortisol and corticosterone. We studied the enzyme kinetics of 11 beta-HSDs in kidney and liver microsomes of the guinea pig, a species whose zoological classification is still a matter of debate. With a fixed concentration of 10(-6) mol/l cortisol, liver and kidney microsomes preferred NAD+ to NADP+ (10(-3) mol/l) for the conversion to cortisone. Kidney microsomes converted cortisol to cortisone with K(m) values of 0.64 mumol/l and 9.8 mumol/l with NAD+ and NADP+ as cosubstrates respectively. The reduction of cortisone to cortisol was slow with kidney microsomes, but could be markedly enhanced by adding an NADH/NADPH regenerating system: with NADPH as preferred cosubstrate, the approximate K(m) was 7.2 mumol/l. This indicated the existence of both isoenzymes in the guinea pig kidney. Liver microsomes oxidized cortisol to cortisone with similar K(m) and Vmax values for NAD+ to NADP+ as cosubstrates (K(m) of 4.3 mumol/l and 5.0 mumol/l respectively). The NAD+ preference for the oxidation of 10(-6) mol/l cortisol described above may be due to a second, NAD(+)-preferring 11 beta-HSD with a K(m) of 1.4 mumol/l. In contrast to the kidney, liver microsomes actively converted cortisone to cortisol with a preference for NADPH (K(m): 1.2 mumol/l; Vmax: 467 nmol/min per mg protein). Thus, the main liver enzyme is similar to the oxidoreductase of other species (11 beta-HSD-I) and is also present in the kidney, while the main kidney enzyme is clearly NAD(+)-preferring. This kidney enzyme (analogous to 11 beta-HSD-II of other species) seems to be suitable for the protection of the MC receptor from the high free plasma cortisol levels of the guinea pig.