Progressive 11ß-Hydroxysteroid Dehydrogenase Type 2 Insufficiency as Kidney Function Declines.

BACKGROUND: It has been postulated that chronic kidney disease (CKD) is a state of relative 11ß-hydroxysteroid dehydrogenase type 2 (11ßHSD2) insufficiency, resulting in increased cortisol-mediated mineralocorticoid receptor (MR) activation. We hypothesized that relative 11ßHSD2 insufficiency manifests across a wide spectrum of progressively declining kidney function, including within the normal range. METHODS: Adult participants were recruited at two academic centers. A discovery cohort (n=500) enrolled individuals with estimated glomerular filtration rate (eGFR) ranging from normal to CKD stage 5, in whom serum cortisol-to-cortisone (F/E) was measured as a biomarker of 11ßHSD2 activity. A validation cohort (n=101) enrolled only individuals with normal kidney function (eGFR ≥ 60 mL/min/1.73 m2) in whom 11ßHSD2 activity was assessed via serum F/E and 11-hydroxy-to-11-keto androgen (11OH/K) ratios following multiple maneuvers: oral sodium suppression test (OSST), dexamethasone suppression test (DST), and ACTH-stimulation test (ACTHstim). RESULTS: In the discovery cohort, lower eGFR was associated with higher F/E (P-trend<0.001). Similarly, in the validation cohort, with normal eGFR, an inverse association between eGFR and both F/E and 11OH/K ratios was observed (P-trend<0.01), which persisted following DST (P-trend<0.001) and ACTHstim (P-trend< 0.05). The fractional excretion of potassium, a marker of renal MR activity, was higher with higher F/E (P-trend < 0.01) and with lower eGFR (P-trend<0.0001). CONCLUSIONS: A continuum of declining 11ßHSD2 activity was observed with progressively lower eGFR in individuals spanning a wide spectrum of kidney function, including those with apparently normal kidney function. These findings implicate cortisol-mediated MR activation in the pathophysiology of hypertension and cardiovascular disease in CKD.

Saline suppression testing-induced hypocalcemia and implications for clinical interpretations.

BACKGROUND: Extracellular calcium critically regulates physiologic aldosterone production. Moreover, abnormal calcium flux and signaling are involved in the pathogenesis of the majority of primary aldosteronism cases. METHODS: We investigated the influence of the saline suppression test (SST) on calcium homeostasis in prospectively recruited participants (n = 86). RESULTS: During SST, 100% of participants had decreases in serum calcium, with 48% developing frank hypocalcemia. Serum calcium declined from 2.30 ± 0.08 mmol/L to 2.13 ± 0.08 mmol/L (P < .001) with parallel increases in parathyroid hormone from 6.06 ± 2.39 pmol/L to 8.13 ± 2.42 pmol/L (P < .001). In contrast, serum potassium and bicarbonate did not change, whereas eGFR increased and serum glucose decreased (P < .001). Lower body surface area (translating to greater effective circulating volume expansion during SST) was associated with greater reductions in (ß = .33, P = .001), and absolutely lower, serum calcium levels (ß = .25, P = .001). When evaluating clinically-relevant diagnostic thresholds, participants with post-SST aldosterone levels <138 pmol/L had lower post-SST calcium and 25-hydroxyvitamin D levels (P < .05), and higher post-SST parathyroid hormone levels (P < .05) compared with those with post-SST aldosterone levels >277 pmol/L. CONCLUSION: SST uniformly decreases serum calcium, which is likely to be due to the combination of variable dilution, increased renal clearance, and vitamin D status. These acute reductions in bioavailable calcium are associated with lower post-SST aldosterone. Given the critical role of extracellular calcium in regulating aldosterone production, these findings warrant renewed inquiry into the validity of SST interpretations for excluding primary aldosteronism.

The Spectrum of Dysregulated Aldosterone Production: An International Human Physiology Study.

CONTEXT: Primary aldosteronism is a form of low-renin hypertension characterized by dysregulated aldosterone production. OBJECTIVE: To investigate the contributions of renin-independent aldosteronism and ACTH-mediated aldosteronism in individuals with a low-renin phenotype representing the entire continuum of blood pressure. DESIGN/PARTICIPANTS: Human physiology study of 348 participants with a low-renin phenotype with severe and/or resistant hypertension, hypertension with hypokalemia, elevated blood pressure and stage I/II hypertension, and normal blood pressure. SETTING: 4 international centers. INTERVENTIONS/MAIN OUTCOME MEASURES: The saline suppression test (SST) to quantify the magnitude of renin-independent aldosteronism; dexamethasone suppression and ACTH-stimulation tests to quantify the magnitude of ACTH-mediated aldosteronism; adrenal venous sampling to determine lateralization. RESULTS: There was a continuum of nonsuppressible and renin-independent aldosterone production following SST that paralleled the magnitude of the blood pressure continuum and transcended conventional diagnostic thresholds. In parallel, there was a full continuum of ACTH-mediated aldosteronism wherein post-SST aldosterone levels were strongly correlated with ACTH-stimulated aldosterone production (r = 0.75, P < .0001) and nonsuppressible aldosterone production postdexamethasone (r = 0.40, P < .0001). Beyond participants who met the criteria for primary aldosteronism (post-SST aldosterone of ≥10 ng/dL or ≥277 pmol/L), the continuum of nonsuppressible and renin-independent aldosterone production persisted below this diagnostic threshold, wherein 15% still had lateralizing aldosteronism amenable to surgical adrenalectomy and the remainder were treated with mineralocorticoid receptor antagonists. CONCLUSION: In the context of a low-renin phenotype, there is a continuum of primary aldosteronism and dysregulated aldosterone production that is prominently influenced by ACTH. A large proportion of individuals with low renin may benefit from aldosterone-directed therapy.