Metabolic and blood pressure responses to hydrocortisone in the syndrome of apparent mineralocorticoid excess

A syndrome of low renin hypertension in childhood with apparent mineralocorticoid excess associated with a defect in the peripheral metabolism of cortisol has been described previously in 2 patients. In these patients, decreased secretion rates of glucocorticoids, mineralocorticoids, and sex steroids have been demonstrated. In a 10(10/12)-yr-old girl with this disorder, continuous iv administration of hydrocortisone in doses of 5, 10, 15, and 20 mg/day resulted in an increase in blood pressure and a decrease in serum potassium concentration. The addition of spironolactone during the continued administration of 20 mg/day hydrocortisone did not result in a decrease in blood pressure. Withdrawal of hydrocortisone and continued administration of spironolactone alone resulted in a decrease in blood pressure, a rise in serum potassium concentration, and a fall in serum sodium concentrations. These studies suggest that an abnormality in cortisol action or metabolism causing cortisol to behave as a potent mineralocorticoid may account for this syndrome of apparent mineralocorticoid excess.     

Apparent mineralocorticoid excess syndrome: an overview

Apparent mineralocorticoid excess (AME) syndrome results from defective 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2). This enzyme is co-expressed with the mineralocorticoid receptor (MR) in the kidney and converts cortisol (F) to its inactive metabolite cortisone (E). Its deficiency allows the unmetabolized cortisol to bind to the MR inducing sodium retention, hypokalemia, suppression of PRA and hypertension. Mutations in the gene encoding 11beta-HSD2 account for the inherited form, but a similar clinical picture to AME occurs following the ingestion of bioflavonoids, licorice and carbenoxolone, which are competitive inhibitors of 11beta-HSD2. Reduced 11beta-HSD2 activity may explain the increased sodium retention in preeclampsia, renal disease and liver cirrhosis. Relative deficiency of 11beta-HSD2 activity can occur in Cushing's syndrome due to saturation of the enzyme and explains the mineralocorticoid excess state that characterizes ectopic ACTH syndrome. Reduced placental 11beta-HSD2 expression might explain the link between reduced birth weight and adult hypertension. Polymorphic variability in the HSD11B2 gene in part determines salt sensitivity, a forerunner for adult hypertension onset. AME represents a spectrum of mineralocorticoid hypertension with severity reflecting the underlying genetic defect in the 11beta-HSD2; although AME is a genetic disorder, several exogenous compounds can bring about the symptoms by inhibiting 11beta-HSD2 enzyme. Substrate excess as seen in Cushing's syndrome and ACTH ectopic production can overwhelm the capacity of 11beta-HSD2 to convert F to E, leading up to an acquired form of AME.     

Apparent mineralocorticoid excess due to 11β-hydroxysteroid dehydrogenase deficiency: a possible cause of intrauterine growth retardation

A Japanese boy with apparent mineralocorticoid excess (AME) is described. He was born with intrauterine growth retardation (IUGR) and elevated serum level of creatine phosphokinase (CPK). He was studied at 2 years of age because of polyurea and polydipsia of one year's duration and was found to have hypokalaemic alkalosis and sustained hypertension. His plasma renin activity and aldosterone levels were always low and his ratio of urinary tetrahydrocortisol plus allo-tetrahydrocortisol to that of tetrahydrocortisone was very high. Therefore, AME due to 11β-hydroxysteroid dehydrogenase (11β-HSD) deficiency was diagnosed. He was successfully treated with a combination of spironolactone and nifedipine for at least 16 months. His blood pressure, plasma pH and serum potassium levels were normalized by this treatment, but serum CPK level remained high.
We researched the birth records of previously reported AME cases and found that IUGR is a characteristic feature of AME. The mechanism by which IUGR occurs in AME is discussed and we speculate that 11β-HSD might be deficient in the placenta and/or fetal tissues, as well as in the kidney, in AME. An explanation for the elevated CPK could not be found.     

Apparent mineralocorticoid excess manifested in an elderly patient with hypothyroidism

The syndrome of apparent mineralocorticoid excess (AME) is characterized by persistent hypertension and hypokalemia, which is caused by impaired inactivation of cortisol (F) to cortisone (E). The thyroid hormone has been known to influence the F to E conversion leading to efficacious inactivation of F into E. However, there have been no reports regarding the clinical manifestation of secondary AME due to hypothyroidism. Here we report an elderly patient who manifested AME, showing persistent hypertension with hypokalemia induced by primary hypothyroidism. Maintenance of euthyroid conditions ameliorated the concurrent AME and restored adrenal secretion of aldosterone after the recovery of the F to E shuttle. This case report would broaden our clinical recognition regarding acquired AME in relation to thyroid dysfunction.     

The role of the 11beta-hydroxysteroid dehydrogenase type 2 in human hypertension

The 11 beta-hydroxysteroid dehydrogenase type 2 (11 PHSD2) enzyme inactivates 11 betahydroxy steroids in sodium-transporting epithelia such as the kidney, thus protecting the non-selective mineralocorticoid receptor (MR) from occupation by cortisol in humans. Inhibition by xenobiotics such as liquorice or mutations in the HSD11 B2 gene, as occur in the rare monogenic hypertensive syndrome of apparent mineralocorticoid excess (AME), result in a compromised 11 betaHSD2 enzyme activity, which in turn leads to overstimulation of the MR by cortisol, sodium retention, hypokalaemia, low plasma renin and aldosterone concentrations, and hypertension. Whereas the first patients described with AME had a severe form of hypertension and metabolic derangements, with an increased urinary ratio of cortisol (THF+5alphaTHF) to cortisone (THE) metabolites, more subtle effects of mild 11 beta HSD2 deficiency on blood pressure have recently been observed. Hypertension with no other characteristic signs of AME was found in the heterozygous father of a child with AME, and we described a girl with a homozygous gene mutation resulting in only a slightly reduced 11 beta HSD2 activity causing 'essential' hypertension. Thus, depending on the degree of loss of enzyme activity, 11 beta HSD2 mutations can cause a spectrum of phenotypes ranging from severe, life-threatening hypertension in infancy to a milder form of the disease in adults. Patients with essential hypertension usually do not have overt signs of mineralocorticoid excess, but nevertheless show a positive correlation between blood pressure and serum sodium levels, or a negative correlation with potassium concentrations, suggesting a mineralocorticoid influence. Recent studies revealed a prolonged half-life of cortisol and an increased ratio of urinary cortisol to cortisone metabolites in some patients with essential hypertension. These abnormalities may be genetically determined. A genetic association of a HSD11 B2 flanking microsatellite and hypertension in black patients with end-stage renal disease has been reported. A recent analysis of a CA-repeat allele polymorphism in unselected patients with essential hypertension did not find a correlation between this marker and blood pressure. Since steroid hormones with mineralocorticoid action modulate renal sodium retention, one might hypothesize that genetic impairment of 11 beta HSD2 activity would be more prevalent in salt-sensitive as compared with salt-resistant subjects. Accordingly, we found a significant association between the polymorphic CA-microsatellite marker and salt-sensitivity. Moreover, the mean ratio of urinary cortisol to cortisone metabolites, as a measure for 11betaHSD2 activity, was markedly elevated in salt-sensitive subjects. These findings suggest that variants of the HSD11 B2 gene may contribute to the enhanced blood pressure response to salt in some humans.     

Late-onset apparent mineralocorticoid excess caused by novel compound heterozygous mutations in the HSD11B2 gene

Mutations in the gene encoding 11beta-hydroxysteroid dehydrogenase type 2, 11beta-HSD2 (HSD11B2), explain the molecular basis for the syndrome of apparent mineralocorticoid excess (AME), characterized by severe hypertension and hypokalemic alkalosis. Cortisol is the offending mineralocorticoid in AME, as the result of a lack of 11beta-HSD2-mediated cortisol to cortisone inactivation. In this study, we describe mutations in the HSD11B2 gene in 3 additional AME kindreds in which probands presented in adult life, with milder phenotypes including the original seminal case reported by Stewart and Edwards. Genetic analysis of the HSD11B2 gene revealed that all probands were compound heterozygotes, for a total of 7 novel coding and noncoding mutations. Of the 7 mutations detected, 6 were investigated for their effects on gene expression and enzyme activity by the use of mutant cDNA and minigene constructs transfected into HEK 293 cells. Four missense mutations resulted in enzymes with varying degrees of activity, all <10% of wild type. A further 2 mutations generated incorrectly spliced mRNA and predicted severely truncated, inactive enzyme. The mothers of 2 probands heterozygous for missense mutations have presented with a phenotype indistinguishable from "essential" hypertension. These genetic and biochemical data emphasize the heterogeneous nature of AME and the effects that heterozygosity at the HSD11B2 locus can have on blood pressure in later life.     

11 beta-hydroxysteroid dehydrogenase and steroid receptors]

11 beta-Hydroxysteroid dehydrogenase (11 beta-HSD), as its name implies, is the enzyme responsible for the conversion of cortisol to cortisone, and of corticosterone to 11-dehydrocorticosterone. Ulick et al. reported the detailed investigation of a patient with the syndrome of apparent mineralocorticoid excess (AME), who had the stigmata of florid hyperaldosteronism but low normal or suppressed levels of renin and aldosterone. Such patients show marked abnormalities of cortisol metabolism. From a series of studies, the consensus grew that AME reflects the absence, or very low activity, of 11 beta-HSD in the kidney of affected patients. In addition to providing a framework for understanding the pathogenesis of AME, these studies prompted a re-evaluation of other areas of steroid in the kidney. Glycyrrhetinic acid, the active principle of liquorice and carbenoxolone, exerted its mineralocorticoid action not by a direct effect on mineralocorticoid receptors but by inhibiting renal 11 beta-HSD, thus producing a mild, drug-induced form of AME. Recently Monder et al. reported the cloning and expression of rat and human cDNA encoding corticosteroid 11 beta-dehydrogenase. The physiological role of 11 beta-HSD in conferring aldosterone-selectivity on otherwise non-selective type I receptors has been focused using the genetic method in addition to the biological ones.     

Biochemical and genetic characterization of 11 beta-hydroxysteroid dehydrogenase type 2 in low-renin essential hypertensives

BACKGROUND: The 11beta-hydroxysteroid dehydrogenase type 2 (11betaHSD2) catalyzes the conversion of cortisol (F) to cortisone (E), avoiding the interaction of cortisol with the mineralocorticoid receptor. If it fails, cortisol will stimulate sodium and water reabsorption, increasing the intravascular volume that suppresses renin and secondarily increase the blood pressure. OBJECTIVE: To look for the possible contribution of a decreased ability of 11betaHSD2 to convert cortisol to its inactive metabolite cortisone in the pathogenesis of low renin hypertension (LREH). PATIENTS AND METHODS: We studied 64 LREH patients (plasma renin activity, PRA < 1 ng/ml per h), eighty normo-renin essential hypertensives (NREH) (PRA: 1-2.5 ng/ml per h) and 74 normotensives. Serum aldosterone (SA), F, E and serum F/E ratio was determined in all patients. A serum F/E ratio was considered high when it was higher than X + 2SD from the normotensive value. Cytosine-adenine (CA)-repeat microsatellite region in intron 1 of HSD11B2 gene was genotyped in all patients and normotensives volunteers. In 13 LREH with high F/E ratio we performed HSD11B2 gene sequencing. RESULTS: LREH had serum F/E ratio higher than NREH and normotensive controls (3.6 (2.9-4.3) versus 2.9 (2.2-4.3) versus 3.0 (2.4-3.7) (P = 0.004), respectively). We observed an inverse relation between F/E ratio and SA and PRA. In NREH and normotensives we did not find correlation between these variables. In the LREH subset the longer 155 bp CA-allele showed the highest serum F/E ratio. No mutations in coding region or short introns were found in LREH patients. CONCLUSION: In this study we show that low-renin essential hypertensives had increased serum cortisol/cortisone ratios as compared with normotensive subjects. This suggest that some essential hypertensives, with suppressed renin activity, may have an impairment in the cortisol inactivation catalyzed by the enzyme 11betaHSD2, whose low activity in LREH patients could be associated with the length of CA-repeat microsatellite in intron 1 of the HSD11B2 gene.     

Does kidney transplantation normalise cortisol metabolism in apparent mineralocorticoid excess syndrome?

The syndrome of apparent mineralocorticoid syndrome (AME) results from defective 11beta-hydroxysteroid dehydrogenase 2 (11beta-HSD2). This enzyme is co-expressed with the mineralocorticoid receptor (MR) in the kidney and converts cortisol to its inactive metabolite cortisone. Its deficiency allows the unmetabolized cortisol to bind to the MR inducing sodium retention, suppression of PRA and hypertension. Thus, the syndrome is a disorder of the kidney. We present here the first patient affected by AME cured by kidney transplantation. Formerly, she was considered to have a mild form of the syndrome (Type II), but progressively she developed renal failure which required dialysis and subsequent kidney transplantation. To test the ability of the transplanted kidney to normalise the patient's cortisol metabolism, we gave, in two different experiments, 25 and 50 mg/day of cortisone acetate or 15 and 30 mg/day of cortisol after inhibition of the endogenous cortisol by synthetic glucocorticoid (methylprednisolone and dexamethasone). The AME diagnostic urinary steroid ratios tetrahydrocortisol+5alphatetrahydrocortisol/tetrahydrocortisone and cortisol/cortisone were measured by gas chromatography/mass spectrometry. Transplantation resulted in lowering blood pressure and in normalization of serum K and PRA. After administration of a physiological dose of cortisol (15 mg/day), the urinary free cortisol/cortisone ratio was corrected (in contrast to the A-ring reduced metabolites ratio), confirming that the new kidney had functional 11beta-HSD2. This ratio was abnormally high when the supra-physiological dose of cortisol 30 mg/day was given. After cortisone administration, the tetrahydrocortisol+5alphatetrahydrocortisol/tetrahydrocortisone ratio resulted normalised with both physiological and supra-physiological doses, confirming that the hepatic reductase activity is not affected. As expected, the urinary free cortisol/cortisone ratio was normal with physiological, but increased after supra-physiological doses of cortisone. The described case indicates a normalisation of cortisol metabolism after kidney transplantation in AME patient and confirms the supposed pathophysiology of the syndrome. Moreover, it suggests a new therapeutic strategy in particularly vulnerable cohorts of patients inadequately responsive to drug therapy or with kidney failure.     

The syndrome of apparent mineralocorticoid excess: its association with 11 beta-dehydrogenase and 5 beta-reductase deficiency and some consequences for corticosteroid metabolism

We describe the metabolism of cortisol (F) in three children, two of them siblings, with apparent mineralocorticoid excess (AME). As with prior patients with AME, oxidation of F to cortisone (E) was impaired, but reduction of E to F was not. We propose that this metabolic defect is caused by deficient 11-dehydrogenase associated with unimpaired 11-reductase. The following supporting observations were made: urinary C21 11-hydroxy metabolites exceeded C21 11-oxo metabolites: ratio of urinary cortols to cortolones, 6.6 +/- 2.8 (+/- SD; normal, 0.47); tetrahydrocortisol (THF) and alloTHF to tetrahydrocortisone, 14.6 +/- 5.6 (normal, approximately 1); normal subjects oxidized [11 alpha-3H]F with transfer of 3H to water; the patients did not; 11-hydroxy, but not 11-oxo, C19 steroids were excreted into the urine; and fibroblasts from patients had 5 times more 11-reductase activity than normal subjects, though fibroblasts from neither group had 11-dehydrogenase activity. Other defects of cortisol metabolism not directly associated with 11-dehydrogenase deficiency were found: impaired conversion of tetrahydro to hexahydro neutral steroids, indicating defective reductive metabolism of the side chain; depressed F production rate and increased half-life of circulating F, resulting in normal blood levels of F; increased excretion of unconjugated F metabolites; and decreased excretion of THF relative to alloTHF, consistent with a 5 beta-reductase defect. Excretion of acidic metabolites of F (cortoic acids) was within the normal range. However, little or no 20 beta-hydroxy acids were excreted, while the level of urinary 20 alpha-hydroxy acids was increased. The 11-hydroxy to 11-oxo ratio of acid metabolites was similar to values in normal subjects. The proportion of cortoic acids relative to neutral hexahydro metabolites was increased (0.37 to 1.27 in patients; 22 in normal subjects). We conclude that children with AME have multiple defects in the conversion of F to neutral metabolites, while metabolism to cortoic acids was less extensively affected. How the defects in cortisol metabolism and the symptoms of AME are related remains to be determined.     

Changes in hormonal activities relative to the severity of essential hypertension.

Endocrine activity in patients with essential hypertension was studied by measuring the urinary excretion of catecholamines, prostaglandin E (PGE) and cyclic adenosine monophosphate (cAMP). Simultaneously, plasma renin activity, concentrations of serum sodium, potassium, blood urea nitrogen (BUN) and creatinine were determined. Systolic blood pressure and BUN increased progressively with age until the sixth decade. Urinary excretion of norepinephrine was correlated with the systolic blood pressure. In contrast, plasma renin activity and urinary excretion of PGE decreased progressively with the increase in systolic blood pressure. Although the cause of essential hypertension is not known, it is suggested that hypertension accelerates the aging process in the kidney and thus decreases renal PGE synthesis. This decrease of PGE in turn causes a reduction of plasma renin activity, possibly either by accelerating the retention of sodium and water or by failing to stimulate renin synthesis. A decrease of PGE may also potentiate the vasopressor action of norepinephrine.     

Glucocorticoids and Hypertension in Man

Abnormalities of cortisol production or metabolism are involved in the genesis of hypertension in Cushing's syndrome, apparent mineralocorticoid excess and liquorice abuse and possibly in chronic renal failure and essential hypertension. We have studied the physiological mechanisms by which cortisol raises blood pressure in short term studies of cortisol administration in normal men. Cortisol induced hypertension cannot be explained by increases in vasopressor or decreases in vasodepressor hormone concentrations, or by any increase in sympathetic nervous activity. The hypertension is accompanied by substantial sodium retention but a significant component of the blood pressure rise is sodium independent. The hypertension is characterized by an increase in cardiac output but a rise in output is not essential for the rise in blood pressure. Our working hypothesis is that cortisol induced hypertension is a consequence of increases in renal vascular resistance.     

A mutation in the cofactor-binding domain of 11beta-hydroxysteroid dehydrogenase type 2 associated with mineralocorticoid hypertension

Renal 11beta-hydroxysteroid dehydrogenase type 2 (11betaHSD2) is an enzyme responsible for the peripheral inactivation of cortisol to cortisone in mineralocorticoid target tissues. Mutations in the gene encoding 11betaHSD2 cause the syndrome of apparent mineralocorticoid excess (AME), an autosomal recessive form of inherited hypertension, in which cortisol acts as a potent mineralocorticoid. The mutations reported to date have been confined to exons 3-5. Here, we describe two siblings, 1 and 2 yr old, who were diagnosed with hypokalemic hypertension and low plasma aldosterone and renin levels, indicating mineralocorticoid hypertension. Analysis of urinary steroid metabolites showed a markedly impaired metabolism of cortisol, with (tetrahydrocortisol + 5alpha-tetrahydrocortisol)/tetrahydrocortisone ratios of 40-60, and nearly absent urinary free cortisone. Although phenotypically normal, the heterozygous parents showed a disturbed cortisol metabolism. Genetic analysis of the HSD11B2 gene from the AME patients revealed the homozygous deletion of six nucleotides in exon 2 with the resultant loss of amino acids Leu(114) and Glu(115), representing the first alteration found in the cofactor-binding domain. The deletion mutant, expressed in HEK-293 cells, showed an approximately 20-fold lower maximum velocity but increased apparent affinity for cortisol and corticosterone. In contrast, two additionally constructed substitutions, Glu(115) to Gln or Lys, showed increased maximal velocity and apparent affinity for 11beta-hydroxyglucocorticoids. Functional analysis of wild-type and mutant proteins indicated that a disturbed conformation of the cofactor-binding domain, but not the missing negative charge of Glu(115), led to the observed decreased activity of the deletion mutant. Considered together, these findings provide evidence for a role of Glu(115) in determining cofactor-binding specificity of 11betaHSD2 and emphasize the importance of structure-function analysis to elucidate the molecular mechanism of AME.     

Mutations in the 11β-Hydroxysteroid Dehydrogenase Type II Enzyme Associated with Hypertension and Possibly Stillbirth

The 11β-hydroxysteroid dehydrogenase type II enzyme (11ßHSD2) converts cortisol into cortisone, thus preventing occupation of the non-selective mineralocorticoid receptor by glucocorticoids in the kidney. Placental 11ßHSD2 is also thought to protect the fetus from the high maternal circulating levels of glucocorticoids. Mutations generating inactive enzymes have been described in the HSD11B2 gene in the congenital syndrome of apparent mineralocorticoid excess (AME) — a low renin form of hypertension. Recently, a mutation has been identified in a family with AME and in which there is a high incidence of stillbirths. In this study we have expressed the R374X mutation and show that the mutant is devoid of enzyme activity in intact mammalian cells expressing a significant level of the truncated protein. While this observation elucidates the cause of AME in this family the degree to which R374X also contributes to the higher incidence of failed pregnancies remains to be determined.     

Mineralocorticoid hypertension

Hypertension with hypokalaemia and suppression of plasma renin activity is known as mineralocorticoid hypertension. Although mineralocorticoid hypertension accounts for a small number of patients labelled as having "essential" hypertension, it is a potentially reversible cause of high blood pressure. The most common cause of mineralocorticoid hypertension is probably primary aldosteronism; controlled posture studies to measure plasma renin activity and aldosterone concentrations, followed by adrenal imaging, will ensure the differential diagnosis between an aldosterone-producing adenoma and idiopathic adrenal hyperplasia in most cases. Three monogenic forms of mineralocorticoid hypertension have been described: glucocorticoid-suppressible hyperaldosteronism, Liddle's syndrome, and apparent mineralocorticoid excess, which have provided new insights into mineralocorticoid hormone action. Many patients with mineralocorticoid-based hypertension are now known to have normal serum potassium concentrations. Until the true prevalence of primary aldosteronism and monogenic forms of mineralocorticoid hypertension are defined, a high index of suspicion is needed in every hypertensive patient. Hypertensive patients with hypokalaemia, together with those with severe hypertension or a family history of hypertension or stroke, should be screened for mineralocorticoid excess.     

11beta-hydroxysteroid dehydrogenase and its role in the syndrome of apparent mineralocorticoid excess.

Aldosterone, the most important mineralocorticoid, regulates electrolyte excretion and intravascular volume mainly through its effects on renal cortical collecting ducts, where it acts to increase sodium resorption from and potassium excretion into the urine. Excess secretion of aldosterone or other mineralocorticoids, or abnormal sensitivity to mineralocorticoids, may result in hypokalemia, suppressed plasma renin activity, and hypertension. The syndrome of apparent mineralocorticoid excess (AME) is an inherited form of hypertension in which 11beta-hydroxysteroid dehydrogenase (11-HSD) is defective. This enzyme converts cortisol to its inactive metabolite, cortisone. Because mineralocorticoid receptors themselves have similar affinities for cortisol and aldosterone, it is hypothesized that the deficiency allows these receptors to be occupied by cortisol, which normally circulates at levels far higher than those of aldosterone. We cloned cDNA and genes encoding two isozymes of 11-HSD. The liver or 11-HSD1 isozyme has relatively low affinity for steroids, is expressed at high levels in the liver but poorly in the kidney, and is not defective in AME. The kidney or 11-HSD2 isozyme has high steroid affinity and is expressed at high levels in the kidney and placenta. Mutations in the gene for the latter isozyme have been detected in all kindreds with AME. Moreover, the in vitro enzymatic activity conferred by each mutation is strongly correlated with the ratio of cortisone to cortisol metabolites in the urine, with age of diagnosis, and with birth weight. This suggests that the biochemical and clinical phenotype of AME is largely determined by genotype.     

Cortisol metabolism in hypertension

Corticosteroids are critically involved in blood pressure regulation. Lack of adrenal steroids in Addison's disease causes life-threatening hypotension, whereas glucocorticoid excess in Cushing's syndrome invariably results in high blood pressure. At a pre-receptor level, glucocorticoid action is modulated by 11beta-hydroxysteroid dehydrogenases (11beta-HSDs). 11Beta-HSD1 activates cortisone to cortisol to facilitate glucocorticoid receptor (GR)-mediated action. By contrast, 11beta-HSD2 plays a pivotal role in aldosterone target tissues where it catalyses the opposite reaction (i.e. inactivation of cortisol to cortisone) to prevent activation of the mineralocorticoid receptor (MR) by cortisol. Mutations in the 11beta-HSD2 gene cause a rare form of inherited hypertension, the syndrome of apparent mineralocorticoid excess (AME), in which cortisol activates the MR resulting in severe hypertension and hypokalemia. Ingestion of competitive inhibitors of 11beta-HSD2 such as liquorice and carbenoxolone result in a similar but milder clinical phenotype. Epidemiological data suggests that polymorphic variability in the HSD11B2 gene determines salt sensitivity in the general population, which is a key predisposing factor to adult onset hypertension in some patients. Extrarenal sites of glucocorticoid action and metabolism that might impact on blood pressure include the vasculature and the central nervous system. Intriguingly, increased exposure to glucocorticoids during fetal life promotes high blood pressure in adulthood suggesting an early programming effect. Thus, metabolism and action in many peripheral tissues might contribute to the pathophysiology of human hypertension.     

Apparent mineralocorticoid excess, 11beta hydroxysteroid dehydrogenase and aldosterone action Closing one loop, opening another.

The recent cloning of the human enzyme 11beta hydroxysteroid dehydrogenase type 2 (11betaHSD2), and the demonstration of point mutations or deletions in both familial and apparently sporadic cases of apparent mineralocorticoid excess (AME), underlines the importance of this enzyme in excluding glucocorticoids from mineralocorticoid receptors (MR). Although the sodium retention characteristic of AME can thus be explained by absent or very reduced (< 10%) levels of renal 11 betaHSD2 activity, whether or not the enzymatic defect contributes to the elevated blood pressure by mechanisms other than sodium retention remains to be determined.     

Angiotensin II stimulates renin in inner medullary collecting duct cells via protein kinase C and independent of epithelial sodium channel and mineralocorticoid receptor activity

Collecting duct (CD) renin is stimulated by angiotensin (Ang) II, providing a pathway for Ang I generation and further conversion to Ang II. Ang II stimulates the epithelial sodium channel via the Ang II type 1 receptor and increases mineralocorticoid receptor activity attributed to increased aldosterone release. Our objective was to determine whether CD renin augmentation is mediated directly by Ang II type 1 receptor or via the epithelial sodium channel and mineralocorticoid receptor. In vivo studies examined the effects of epithelial sodium channel blockade (amiloride; 5 mg/kg per day) on CD renin expression and urinary renin content in Ang II-infused rats (80 ng/min, 2 weeks). Ang II infusion increased systolic blood pressure, medullary renin mRNA, urinary renin content, and intrarenal Ang II levels. Amiloride cotreatment did not alter these responses despite a reduction in the rate of progression of systolic blood pressure. In primary cultures of inner medullary CD cells, renin mRNA and (pro)renin protein levels increased with Ang II (100 nmol/L), and candesartan (Ang II type 1 receptor antagonist) prevented this effect. Aldosterone (10(-10) to 10(-7) mol/L) with or without amiloride did not modify the upregulation of renin mRNA in Ang II-treated cells. However, inhibition of protein kinase C with calphostin C prevented the Ang II-mediated increases in renin mRNA and (pro)renin protein levels. Furthermore, protein kinase C activation with phorbol 12-myristate 13-acetate increased renin expression to the same extent as Ang II. These data indicate that an Ang II type 1 receptor-mediated increase in CD renin is induced directly by Ang II via the protein kinase C pathway and that this regulation is independent of mineralocorticoid receptor activation or epithelial sodium channel activity.