Are the hypokalaemia and hypertension in Cushing's disease caused by apparent mineralocorticoid excess?

11β-hydroxystéroïde déshydrogénases. Avancées récentes

11beta-hydroxysteroide dehydrogenase (11beta-OHSD) enzymes exhibit a regulating action upon cortisol metabolism before access to its receptors. Two types of isoenzymes have been described, type 2 being the most anciently known. Type 2 11beta-OHSD, which changes cortisol into cortisone, is a unidirectional dehydrogenase mainly located in kidney, that protects mineralocorticoid receptors from illicit activation by glucocorticoids. Mutations of the gene coding for this enzyme has been demonstrated in apparent mineralocorticoid excess, which induces hypertension and hypokalemia with low renin and aldosterone levels. Polymorphisms of this gene could modulate essential hypertension and also be responsible for certain forms of acquired apparent mineralocorticoid excess especially after liquorice intoxication, in hypothyroidism, Cushing syndrome, and chronic renal insufficiency. Type 1 11beta-OHSD, which changes cortisone into cortisol, is a reductase, mainly located in liver and adipose tissue. Functional defects of this enzyme have been shown in polycystic ovaries and cortisone reductase deficiency. By contrast, metabolic syndrome, corticoid-induced osteoporosis, and glaucoma are linked to a local over-activity of this enzyme. The understanding of action mechanisms of these two enzymes currently leads to 11beta-OHSD inhibitors development, therefore opening new therapeutic strategies, especially in metabolic syndrome.

Glucocorticoids and the kidney. Review Article

Glucocorticoids are widely used by nephrologists for their immunomodulatory and anti-inflammatory effects. The present review considers three aspects of glucocorticoids with which nephrologists may be less familiar: (i) renal metabolism; (ii) effects on renal haemodynamics; and (iii) effects on blood pressure as they relate to the kidney.

Acute intrarenal administration of cortisol has no effect on renal blood flow in hypertensive individuals

BACKGROUND

Cortisol is known to increase blood pressure. One possible mechanism is the reported increase in renal vascular resistance (RVR). It is unknown whether this is due to a direct effect of cortisol on the kidneys.

OBJECTIVE

To study the effect of infusion of cortisol directly into the renal artery on renal blood flow (RBF) and on renal 11beta-hydroxysteroid dehydrogenase (11beta-HSD)-mediated conversion of cortisol to cortisone in patients with primary hypertension.

DESIGN AND METHODS

Twenty-seven patients with primary hypertension participated in this study. Fifteen received placebo and 12 received glycyrrhetinic acid (GRA; 500 mg) orally 2.5 h before the study. After a 10 min infusion of 5% glucose, cortisol was infused in stepwise increasing doses (0.625, 1.25 and 2.5 microg/kg per min), for 10 min each dose. At the end of each infusion step, RBF was measured using the xenon-133 washout technique. Plasma samples from the femoral artery and renal vein were taken for measurement of cortisol and cortisone. Urine was collected for measurement of steroid concentrations for 6 h on the day before the infusion and for 6 h after the infusion.

RESULTS

After placebo or GRA, cortisol infusion did not change RVR, RBF or blood pressure. RVR values were 0.72 (0.45-0.89) mmHg/ml per min per 100 ml tissue [median (first and third quartiles)] and 0.71 (0.64-0.91) mmHg/ml per min per 100 ml tissue during infusion of 5% glucose and infusion of the highest dose of cortisol, respectively ( P= NS). Cortisol infusion increased the venous-arterial difference in plasma cortisone concentration across the kidney from 76 (40-115) nmol/l to 138 (100-186) nmol/l (P< 0.05) and increased the cortisol : cortisone ratios in the renal vein and in urine (both P< 0.05). As compared with placebo, administration of GRA increased the cortisol : cortisone ratios in peripheral and renal veins and in the urine.

CONCLUSION

Acute infusion of cortisol in high doses directly into the renal artery in patients with primary hypertension did not affect RBF or RVR. Infusion of cortisol resulted in increased cortisol-cortisone conversion by renal 11beta-HSD2, but the concurrent increase in renal and urinary cortisol : cortisone ratio suggests a relative insufficiency of renal 11beta-HSD2 activity as a result of enzyme saturation. This may enhance mineralocorticoid receptor stimulation by cortisol.

Investigation of the role of aldosterone in hypertension associated with spontaneous pituitary-dependent hyperadrenocorticism in dogs

The aim of this study was to evaluate the role of aldosterone as an initiating and/or perpetuating factor in hypertension associated with pituitary-dependent hyperadrenocorticism (PDH) in dogs. Thirteen dogs with PDH and 11 healthy control dogs were used. In all dogs, arterial blood pressure and plasma sodium, potassium, basal aldosterone, post-ACTH aldosterone, basal cortisol and post-ACTH cortisol concentrations were measured. The tests were repeated 10 days and three months after the beginning of o,p'-DDD treatment in PDH dogs. In untreated PDH dogs, plasma aldosterone was significantly decreased, whereas cortisol, sodium and arterial blood pressure were significantly increased compared to healthy dogs. Hypertension remained in most treated PDH dogs despite normalisation of cortisol and persistently low aldosterone levels. These results did not demonstrate that aldosterone is involved in the development and perpetuation of hypertension in PDH. However, glucocorticoids seemed to play a major role as an initiating and perpetuating factor in PDH in dogs.

Association of hypertension and hypokalemia with Cushing's syndrome caused by ectopic ACTH secretion: a series of 58 cases

Cushing's syndrome is associated with hypertension in approximately 80% of cases. Hypertension contributes to the marked increased mortality risk of past or current Cushing's syndrome, largely because of increased cardiovascular risk. Observation of the pathophysiological effect of chronically elevated ACTH and cortisol values in patients with ectopic ACTH secretion complements the available data from acute studies of the effects of ACTH and glucocorticoid infusions in normal volunteers. In a retrospective case review, we identified 58 patients with Cushing's syndrome caused by ectopic ACTH secretion, who were treated at the National Institutes of Health between 1983-1997. The diagnosis of an ectopic ACTH cause was confirmed by inferior petrosal sinus sampling and/or pathologic examination of tumor. The commonest causes were bronchial carcinoid (40%) and thymic carcinoid (10%), but 18 of 58 (31%) patients had an unknown source of ectopic ACTH. Hypertension (systolic blood pressure >140 mmHg and/or diastolic blood pressure >90 mmHg in adults) was noted in 45 of 58 (78%) ectopic Cushing's patients, a prevalence similar to that noted in other endogenous Cushing's syndrome etiologies. Hypertension was severe, deemed to require 3 or more drugs by the treating physicians, in 26 of 58 (45%) patients. Hypokalemia was much more prevalent than in patients with other causes of Cushing's syndrome, affecting 33 of 58 (57%) patients. The range of plasma ACTH (17-1557 pg/mL, normal <60) and 24-hour urine cortisol (UC) excretion (192-1600 mcg/24 hr, normal <90) allowed analysis of the influence of these hormones on blood pressure and plasma potassium. There was a significant relationship between 24-hour UC excretion and the presence of hypokalemia (P = 0.003). Eight of nine patients with a UC >6000 mcg/24 hr had hypokalemia. There was no relation between ACTH level and hypokalemia. In addition, we did not find blood pressure severity to be related to UC excretion or ACTH levels. Urine and plasma cortisol and cortisol metabolite measurements suggest that cortisol may act as a mineralocorticoid when in excess, perhaps by saturating the 11beta-hydroxysteroid-dehydrogenase (11beta-HSD2 enzyme) that inactivates cortisol at the renal tubule. The current data suggest that high cortisol levels may be the principal cause of hypokalemic alkalosis in Cushing's syndrome, rather than inhibition of the 11betaHSD2 enzyme by ACTH or the effects of adrenal steroid biosynthetic intermediaries with mineralococorticoid activity.

Molecular genetics of human blood pressure variation

Hypertension is a common multifactorial vascular disorder of largely unknown cause. Recognition that hypertension is in part genetically determined has motivated studies to identify mutations that confer susceptibility. Thus far, mutations in at least 10 genes have been shown to alter blood pressure; most of these are rare mutations imparting large quantitative effects that either raise or lower blood pressure. These mutations alter blood pressure through a common pathway, changing salt and water reabsorption in the kidney. These findings demonstrate the utility of molecular genetic approaches to the understanding of blood pressure variation and may provide insight into the physiologic mechanisms underlying common forms of hypertension.

Elevated plasma 19-hydroxyandrostenedione levels in Cushing's disease: stimulation with ACTH and inhibition with metyrapone

OBJECTIVE

The regulation of 19-hydroxyandrostenedione secretion has been suggested to be under the control of both the ACTH-adrenal axis and renin-angiotensin system. We undertook the present study to evaluate the effect of the chronic excess of ACTH, or the short-term excess of ACTH due to metyrapone, on 19-hydroxyandrostenedione secretion in patients with Cushing's disease.

DESIGN AND PATIENTS

We measured plasma 19-hydroxyandrostenedione levels simultaneously with plasma delta 4-androstenedione, corticosterone, 11-deoxycorticosterone, aldosterone and cortisol levels after HPLC separation in 13 patients with Cushing's disease under basal conditions and during a dexamethasone suppression test or metyrapone test. Seven patients with Cushing's syndrome due to adrenal adenoma were used for comparison.

RESULTS

The basal levels of 19-hydroxyandrostenedione in Cushing's disease were elevated (mean +/- SD; 323 +/- 193 pmol/l, n = 13), while those in Cushing's syndrome due to adrenal adenoma were low (92 +/- 24 pmol/l, n = 7), compared to those in normal subjects (117 +/- 33 pmol/l, n = 54). The basal levels of delta 4-androstenedione were mildly elevated in Cushing's disease (9.0 +/- 6.5 vs 3.6 +/- 2.6 nmol/l of normal subjects) but not in Cushing's syndrome due to adrenal adenoma (3.1 +/- 3.0 nmol/l). In the overnight 8 mg dexamethasone suppression test in Cushing's disease (n = 12), plasma levels of 19-hydroxyandrostenedione and delta 4-androstenedione decreased from 277 +/- 172 to 156 +/- 99 pmol/l and from 9.2 +/- 6.8 to 4.7 +/- 3.4 nmol/l, respectively, whereas the overnight 1 mg dexamethasone suppression test did not induce significant changes. Metyrapone administration in Cushing's disease (n = 9) increased plasma delta 4-androstenedione level from 9.5 +/- 6.7 to 47.2 +/- 28.1 nmol/l, but decreased plasma 19-hydroxyandrostenedione level from 301 +/- 196 to 196 +/- 105 pmol/l.

CONCLUSIONS

These data indicate that plasma levels of 19-hydroxyandrostenedione in patients with Cushing's disease are elevated due to chronic ACTH excess, and that metyrapone can inhibit 19-hydroxylation in humans.