Effects of Empagliflozin in Type 2 Diabetes With and Without Chronic Kidney Disease and Nondiabetic Chronic Kidney Disease: Protocol for 3 Crossover Randomized Controlled Trials (SiRENA Project).

BACKGROUND: Sodium-glucose-cotransporter 2 inhibitors (SGLT2is) have revolutionized the treatment of type 2 diabetes mellitus (DM2) and chronic kidney disease (CKD), reducing the risk of cardiovascular and renal end points by up to 40%. The underlying mechanisms are not fully understood. OBJECTIVE: The study aims to examine the effects of empagliflozin versus placebo on renal hemodynamics, sodium balance, vascular function, and markers of the innate immune system in patients with DM2, DM2 and CKD, and nondiabetic CKD. METHODS: We conducted 3 double-blind, crossover, randomized controlled trials, each with identical study protocols but different study populations. We included patients with DM2 and preserved kidney function (estimated glomerular filtration rate >60 mL/min/1.73 m2), DM2 and CKD, and nondiabetic CKD (both with estimated glomerular filtration rate 20-60 mL/min/1.73 m2). Each participant was randomly assigned to 4 weeks of treatment with either 10 mg of empagliflozin once daily or a matching placebo. After a wash-out period of at least 2 weeks, participants were crossed over to the opposite treatment. End points were measured at the end of each treatment period. The primary end point was renal blood flow measured with 82Rubidium positron emission tomography-computed tomography (82Rb-PET/CT). Secondary end points include glomerular filtration rate measured with 99mTechnetium-diethylene-triamine-pentaacetate (99mTc-DTPA) clearance, vascular function assessed by forearm venous occlusion strain gauge plethysmography, measurements of the nitric oxide (NO) system, water and sodium excretion, body composition measurements, and markers of the complement immune system. RESULTS: Recruitment began in April 2021 and was completed in September 2022. Examinations were completed by December 2022. In total, 49 participants completed the project: 16 participants in the DM2 and preserved kidney function study, 17 participants in the DM2 and CKD study, and 16 participants in the nondiabetic CKD study. Data analysis is ongoing. Results are yet to be published. CONCLUSIONS: This paper describes the rationale, design, and methods used in a project consisting of 3 double-blind, crossover, randomized controlled trials examining the effects of empagliflozin versus placebo in patients with DM2 with and without CKD and patients with nondiabetic CKD, respectively. TRIAL REGISTRATION: EU Clinical Trials Register 2019-004303-12; https://www.clinicaltrialsregister.eu/ctr-search/search?query=2019-004303-12, EU Clinical Trials Register 2019-004447-80; https://www.clinicaltrialsregister.eu/ctr-search/search?query=2019-004447-80, EU Clinical Trials Register 2019-004467-50; https://www.clinicaltrialsregister.eu/ctr-search/search?query=and+2019-004467-50. INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID): DERR1-10.2196/56067.

Reliability of rubidium-82 PET/CT for renal perfusion determination in healthy subjects.

BACKGROUND: Changes in renal perfusion may play a pathophysiological role in hypertension and kidney disease, however to date, no method for renal blood flow (RBF) determination in humans has been implemented in clinical practice. In a previous study, we demonstrated that estimation of renal perfusion based on a single positron emission tomography/computed tomography (PET/CT) scan with Rubidium-82 (82Rb) is feasible and found an approximate 5% intra-assay coefficient of variation for both kidneys, indicative of a precise method.This study's aim was to determine the day-to day variation of 82Rb PET/CT and to test the method's ability to detect increased RBF induced by infusion of amino acids. METHODS: Seventeen healthy subjects underwent three dynamic 82Rb PET/CT scans over two examination days comprising: Day A, a single 8-minute dynamic scan and Day B, two scans performed before (baseline) and after RBF stimulation by a 2-hour amino acid-infusion. The order of examination days was determined by randomization. Time activity curves for arterial and renal activity with a 1-tissue compartment model were used for flow estimation; the K1 kinetic parameter representing renal 82Rb clearance. Day-to-day variation was calculated based on the difference between the unstimulated K1 values on Day A and Day B and paired t-testing was performed to compare K1 values at baseline and after RBF stimulation on Day B. RESULTS: Day-to-day variation was observed to be 5.5% for the right kidney and 6.0% for the left kidney (n = 15 quality accepted scans). K1 values determined after amino acid-infusion were significantly higher than pre-infusion values (n = 17, p = 0.001). The mean percentage change in K1 from baseline was 13.2 ± 12.9% (range - 10.4 to 35.5) for the right kidney; 12.9 ± 13.2% (range - 15.7 to 35.3) for the left kidney. CONCLUSION: Day-to-day variation is acceptably low. A significant K1 increase from baseline is detected after application of a known RBF stimulus, indicating that 82Rb PET/CT scanning can provide a precise method for evaluation of RBF and it is able to determine changes herein. CLINICAL TRIAL REGISTRATION: EU Clinical Trials Register, 2017-005008-88. Registered 18/01/2018.

Renal Artery Stenting in Consecutive High-Risk Patients With Atherosclerotic Renovascular Disease: A Prospective 2-Center Cohort Study.

Background The aim of this study was to prospectively evaluate the effects of renal artery stenting in consecutive patients with severe atherosclerotic renal artery stenosis and high-risk clinical presentations as defined in a national protocol developed in 2015. Methods and Results Since the protocol was initiated, 102 patients have been referred for revascularization according to the following high-risk criteria: severe renal artery stenosis (≥70%) with true resistant hypertension, rapidly declining kidney function, or recurrent heart failure/sudden pulmonary edema. At baseline, the mean 24-hour ambulatory systolic blood pressure was 166.2 mm Hg (95% CI, 162.0-170.4), the defined daily dose of antihypertensive medication was 6.5 (95% CI, 5.8-7.3), and the estimated glomerular filtration rate was 41.1 mL/min per 1.73m2 (95% CI, 36.6-45.6). In 96 patients with available 3-month follow-up data, mean 24-hour ambulatory systolic blood pressure decreased by 19.6 mm Hg (95% CI, 15.4-23.8; P<0.001), the defined daily dose of antihypertensive medication was reduced by 52% (95% CI, 41%-62%; P<0.001), and estimated glomerular filtration rate increased by 7.8 mL/min per 1.73m2 (95% CI, 4.5-11.1; P<0.001). All changes persisted after 24 month follow-up. Among 17 patients with a history of hospitalization for acute decompensated heart failure, 14 patients had no new episodes after successful revascularization. Conclusions In this prospective cohort study, we observed a reduction in blood pressure and antihypertensive medication, an increase in estimated glomerular filtration rate, and a decrease in new hospital admissions attributable to heart failure/sudden pulmonary edema after renal artery stenting. Registration URL: https://clinicaltrials.gov. Identifier: NCT02770066.

[Diabetic muscle infarction as a rare cause of acute onset leg pain].

Diabetic muscle infarction (DMI) is a rare microvascular complication with spontaneous necrosis of skeletal musculature, most often localised to the thigh. DMI presents as an acute onset of pain in a muscle or muscle group. DMI is probably underdiagnosed because of its rareness and many differential diagnoses, why patients often undergo unnecessary and invasive diagnostic testing. The condition can be diagnosed with magnetic resonance imaging and the treatment is supportive with analgesics, bedrest and glycaemic control. We present two cases of DMI in patients with long-standing Type 1 diabetes.

Estimation of renal perfusion based on measurement of rubidium-82 clearance by PET/CT scanning in healthy subjects.

BACKGROUND: Changes in renal blood flow (RBF) may play a pathophysiological role in hypertension and kidney disease. However, RBF determination in humans has proven difficult. We aimed to confirm the feasibility of RBF estimation based on positron emission tomography/computed tomography (PET/CT) and rubidium-82 (82Rb) using the abdominal aorta as input function in a 1-tissue compartment model. METHODS: Eighteen healthy subjects underwent two dynamic 82Rb PET/CT scans in two different fields of view (FOV). FOV-A included the left ventricular blood pool (LVBP), the abdominal aorta (AA) and the majority of the kidneys. FOV-B included AA and the kidneys in their entirety. In FOV-A, an input function was derived from LVBP and from AA, in FOV-B from AA. One-tissue compartmental modelling was performed using tissue time activity curves generated from volumes of interest (VOI) contouring the kidneys, where the renal clearance of 82Rb is represented by the K1 kinetic parameter. Total clearance for both kidneys was calculated by multiplying the K1 values with the volume of VOIs used for analysis. Intra-assay coefficients of variation and inter-observer variation were calculated. RESULTS: For both kidneys, K1 values derived from AA did not differ significantly from values obtained from LVBP, neither were significant differences seen between AA in FOV-A and AA in FOV-B, nor between the right and left kidneys. For both kidneys, the intra-assay coefficients of variation were low (~ 5%) for both input functions. The measured K1 of 2.80 ml/min/cm3 translates to a total clearance for both kidneys of 766 ml/min/1.73 m2. CONCLUSION: Measurement of renal perfusion based on PET/CT and 82Rb using AA as input function in a 1-tissue compartment model is feasible in a single FOV. Based on previous studies showing 82Rb to be primarily present in plasma, the measured K1 clearance values are most likely representative of effective renal plasma flow (ERPF) rather than estimated RBF values, but as the accurate calculation of total clearance/flow is very much dependent on the analysed volume, a standardised definition for the employed renal volumes is needed to allow for proper comparison with standard ERPF and RBF reference methods.

Effect of furosemide on body composition and urinary proteins that mediate tubular sodium and sodium transport-A randomized controlled trial.

BACKGROUND: Furosemide inhibits the sodium potassium chloride cotransporter (NKCC2) in the thick ascending limb of the loop of Henle and increases urinary water and sodium excretion. This study investigates the effect of furosemide on body composition estimated with multifrequency bioimpedance spectroscopy (BIS) technique and urinary proteins from NKCC2. METHODS: This study is a randomized, placebo-controlled, crossover study where healthy subjects received either placebo or 40 mg furosemide on two separate occasions, where body composition with BIS, renal function, proteins from tubular proteins that mediate sodium and water transport, and plasma concentrations of vasoactive hormones were measured before and after intervention. RESULTS: We observed an expected increased diuresis with a subsequent reduction in bodyweight of (-1.51 ± 0.36 kg, p < .001) and extracellular water (ECW; -1.14 ± 0.23 L, p < .001) after furosemide. We found a positive correlation between the decrease in ECW and a decrease in bodyweight and a negative correlation between the decrease in ECW and the increase in urinary output. Intracellular water (ICW) increased (0.47 ± 0.28 L, p < .001). Urinary excretion of NKCC2 increased after furosemide and the increase in NKCC2 correlated with an increase in urine output and a decrease in ECW. CONCLUSION: We found BIS can detect acute changes in body water content but the method may be limited to estimation of ECW. BIS demonstrated that furosemide increases ICW which might be explained by an extracellular sodium loss. Finally, urinary proteins from NKCC2 increases after furosemide with a good correlation with diuresis end the decrease in ECW.

Comparison of Ambulatory Tonometric and Oscillometric Blood Pressure Monitoring in Hypertensive Patients.

AIM: Correct measurement of blood pressure (BP) is important for optimal diagnosis and treatment of patients with hypertension. The aim of this study was to compare a wrist-worn device using tonometric measurements of BP to a conventional device using oscillometric measurements of 24 h BP, diagnosing of hypertension, and non-dipping. METHODS: One-hundred patients in the Renal Outpatient Clinic had 24 h ambulatory BP monitoring performed with a tonometric device, BPro, and an oscillometric device, A&D, simultaneously. RESULTS: Twenty-four-hour and daytime systolic BP was significantly lower using tonometric monitoring compared to oscillometric (7 and 6 mmHg, respectively, p< 0.001). In the population of patients diagnosed with hypertension, the tonometric device diagnosed 90% of patients with uncontrolled hypertension correctly (positive predictive value), whereas 49% of patients classified as normotensive were uncontrolled hypertensive (negative predictive value). The mean difference between relative nocturnal BP decrease between tonometric and oscillometric was 2±8% (p< 0.01), and 33% of patients classified as dippers were non-dippers (negative predictive value). CONCLUSION: Using the BPro device for tonometric monitoring of BP and classification of hypertension and non-dipping in patients diagnosed with hypertension leads to misclassification of patients. Therefore, the BPro device is not suitable for clinical practice in hypertensive patients from a Renal Outpatient Clinic.

Effects of lung protective ventilation on postoperative respiratory parameters in patients undergoing robot-assisted radical prostatectomy.

To investigate the effects of lung protective ventilation (LPV) compared to conventional ventilation (CV) on postoperative respiratory parameters in patients undergoing robot-assisted radical prostatectomy (RARP). In total, 24 patients undergoing RARP were randomized to two groups receiving either LPV with a tidal volume of 6 ml/IBW with a positive end-expiratory pressure (PEEP) of 10 cm H2O (intervention) or CV with a tidal volume of 10 ml/IBW with a PEEP of 4 cmH2O (control). Primary endpoint was PaO2 2 h postoperatively after 10 min of spontaneous respiration of atmospheric air. Forced expiratory volume during the first second (FEV1), forced vital capacity (FVC), diffusion capacity (DLCO), and plasma interleukin-6 (IL-6) was measured before and after the surgery. Pulmonary complications were registered within the first year after surgery. All patients completed the study. No difference was found in PaO2 between LPV and CV. However, 4 patients in the LPV group had a decrease in saturation below 90% during the 10 min of spontaneous respiration of atmospheric air compared to none in the CV group. FEV1, FVC, and DLCO were similar when comparing the two groups at all timepoints and no patients in either of the groups had pulmonary complications during the first postoperative year. IL-6 levels increased during surgery in both groups, but were not significantly different between the two groups. We found no evidence of lung protective effects of LPV compared to CV estimated by pulmonary function tests, IL-6 levels and postoperative complications in patients undergoing RARP. Surprisingly, only patients in the LPV group and none in the CV group had a decline in saturation below 90% during the 10 min of breathing atmospheric air.

The effect of vitamin D3 supplementation on markers of cardiovascular health in hyperparathyroid, vitamin D insufficient women: a randomized placebo-controlled trial.

PURPOSE: Emerging data supports an association between parathyroid hormone (PTH) and aldosterone. It has been speculated, that potential adverse cardiovascular effects of vitamin D insufficiency may partly be caused by the development of secondary hyperparathyroidism with increased activity of the renin-angiotensin-aldosterone system (RAAS). We aimed to investigate the effect of normalizing vitamin D status and/or reducing PTH levels on RAAS activity and other markers of cardiovascular health. METHODS: In a double-blinded study during wintertime, we randomized 81 healthy postmenopausal women with secondary hyperparathyroidism (PTH > 6.9 pmol/l) and 25-hydroxy-vitamin D (25(OH)D) levels < 50 nmol/l to 12 weeks of treatment with vitamin D3 70 µg/day (2800 IU/day) or identical placebo. Markers of cardiovascular health were defined as changes in the plasma RAAS, glycated hemoglobin, lipids, and lipoproteins, blood pressure, vascular stiffness, heart rate, and cardiac conductivity. RESULTS: Compared to placebo, vitamin D3 treatment significantly increased plasma levels of 25(OH)D and 1,25(OH)2D by 230% (95% CI: 189-272%) and 58% (190-271%), respectively. Vitamin D3 treatment reduced PTH by 17% (11-23%), but did not reduce RAAS activity. Compared to placebo, vitamin D3 treatment increased plasma levels of high-density lipoproteins (HDL) by 4.6% (0.12-9.12%), but did not affect other measured indices. CONCLUSIONS: Vitamin D3 supplementation normalized vitamin D levels and reduced PTH. The supplement increased levels of HDL, but had no effects on RAAS activity or other indices of cardiovascular health.

Effect of tolvaptan on renal water and sodium excretion and blood pressure during nitric oxide inhibition: a dose-response study in healthy subjects.

BACKGROUND: Tolvaptan is a selective vasopressin receptor antagonist. Nitric Oxide (NO) promotes renal water and sodium excretion, but the effect is unknown in the nephron's principal cells. In a dose-response study, we measured the effect of tolvaptan on renal handling of water and sodium and systemic hemodynamics, during baseline and NO-inhibition with L-NMMA (L-NG-monomethyl-arginine). METHODS: In a randomized, placebo-controlled, double blind, cross over study, 15 healthy subjects received tolvaptan 15, 30 and 45 mg or placebo. L-NMMA was given as a bolus followed by continuous infusion during 60 min. We measured urine output (UO), free water clearance (CH2O), fractional excretion of sodium (FENa), urinary aquaporin-2 channels (u-AQP2) and epithelial sodium channels (u-ENaCγ), plasma vasopressin (p-AVP) and central blood pressure (cBP). RESULTS: During baseline, FENa was unchanged. Tolvaptan decreased u-ENaCγ dose-dependently and increased p-AVP threefold, whereas u-AQP2 was unchanged. During tolvaptan with NO-inhibition, UO and CH2O decreased dose-dependently. FENa decreased dose-independently and u-ENaCγ remained unchanged. Central BP increased equally after all treatments. CONCLUSIONS: During baseline, fractional excretion of sodium was unchanged. During tolvaptan with NO-inhibition, renal water excretion was reduced dose dependently, and renal sodium excretion was reduced unrelated to the dose, partly via an AVP dependent mechanism. Thus, tolvaptan antagonized the reduction in renal water and sodium excretion during NO-inhibition. Most likely, the lack of decrease in AQP2 excretion by tolvaptan could be attributed to a counteracting effect of the high level of p-AVP. TRIAL REGISTRATION: Clinical Trial no: NCT02078973 . Registered 1 March 2014.

High Prevalence of Hypertension in a Danish Population Telemedical Home Measurement of Blood Pressure in Citizens Aged 55-64 Years in Holstebro County.

BACKGROUND: Home blood pressure (HBP) is prognostically superior to office BP (OBP) and similar to ambulatory BP measurements. We determined the prevalence of hypertension using HBP with telemedical data transmission in the municipality of Holstebro, Denmark (57,000 citizens). METHODS: Using the Civil Registration System, we invited citizens aged 55-64 years to have their OBP and HBP measured using telemedical data transmission. Elevated OBP was defined as ≥140/90mm Hg. HBP was measured 3 times daily on 3 consecutive days with 3 measurements on each occasion. HBP was the mean of all measurements on day 1 and 3, and hypertension was defined as ≥135/85mm Hg. RESULTS: We included 3,102 citizens who had performed at least 12 HBP measurements during day 2 and 3. Group 1: (n = 1,464, 47%) had both normal OBP and HBP. Group 2: (n = 838, 27%) had both elevated OBP and HBP indicating persistent hypertension. Group 3: (n = 560, 18%) had elevated OBP and normal HBP indicating white coat hypertension (WCH). Group 4: (n = 240, 8%) had normal OBP and elevated HBP indicating masked hypertension (MH). Thus, 1,078 (35%, groups 2 and 4) were untreated or insufficiently treated. Awareness of hypertension was registered in 950 patients (31%) and of these 49% had a normal HBP. CONCLUSIONS: This is the first large-scale study to eliminate completely reporting bias by using telemedical transmission of BP data. One third of citizens in the age group 55-64 years had an abnormally high HBP, and one fourth either had WCH or MH. CLINICAL TRIALS REGISTRATION: ClinicalTrials.gov identification number: NCT02355392.

Effect of vasopressin antagonism on renal handling of sodium and water and central and brachial blood pressure during inhibition of the nitric oxide system in healthy subjects.

BACKGROUND: Tolvaptan is a selective vasopressin receptor antagonist (V2R) that increases free water excretion. We wanted to test the hypotheses that tolvaptan changes both renal handling of water and sodium and systemic hemodynamics during basal conditions and during nitric oxide (NO)-inhibition with L-NG-monomethyl-arginine (L-NMMA). METHODS: Nineteen healthy subjects were enrolled in a randomized, placebo-controlled, double-blind, crossover study of two examination days. Tolvaptan 15 mg or placebo was given in the morning. L-NMMA was given as a bolus followed by continuous infusion during 60 minutes. We measured urine output(UO), free water clearance (CH2O), fractional excretion of sodium (FENa), urinary aquaporin-2 channels (u-AQP2) and epithelial sodium channels (u-ENaCγ), plasma vasopressin (p-AVP), central and brachial blood pressure(cBP, bBP). RESULTS: During baseline conditions, tolvaptan caused a significant increase in UO, CH2O and p-AVP, and FENa was unchanged. During L-NMMA infusion, UO and CH2O decreased more pronounced after tolvaptan than after placebo (-54 vs.-42% and -34 vs.-9% respectively). U-AQP2 decreased during both treatments, whereas u-ENaCγ decreased after placebo and increased after tolvaptan. CBP and bBP were unchanged. CONCLUSION: During baseline conditions, tolvaptan increased renal water excretion. During NO-inhibition, the more pronounced reduction in renal water excretion after tolvaptan indicates that NO promotes water excretion in the principal cells, at least partly, via an AVP-dependent mechanism. The lack of decrease in u-AQP2 by tolvaptan could be explained by a counteracting effect of increased plasma vasopressin. The antagonizing effect of NO-inhibition on u-ENaC suggests that NO interferes with the transport via ENaC by an AVP-dependent mechanism.

Effects of atorvastatin on systemic and renal NO dependency in patients with non-diabetic stage II-III chronic kidney disease.

AIMS: Clinical trials suggest that statins have beneficial effects on the cardiovascular system independent from their cholesterol lowering properties. In patients with chronic kidney disease stage II-III, we tested the hypothesis that atorvastatin increased systemic and renal nitric oxide (NO) availability using L-N(G) -monomethyl arginine (L-NMMA) as an inhibitor of NO production. METHODS: In a randomized, placebo-controlled, crossover study patients were treated with atorvastatin for 5 days with standardized diet and fluid intake. Glomerular filtration reate (GFR), fractional excretions of sodium (FENa ), urinary excretion of aquaporin-2 (u-AQP2) and epithelial sodium channels (u-ENaCγ ), vasoactive hormones (renin, angiotensin II, aldosterone, arginine vasopressin, endothelin-1 and brain natriuretic peptide) and central blood pressure (BP) estimated by applanation tonometry were measured before and after systemic administration of the NO inhibitor L-NMMA. RESULTS: Atorvastatin caused a significant reduction in U-ENaCγ , but sodium excretion, C H 2 O , FENa and u-AQP2 were not changed by atorvastatin. L-NMMA reduced renal effect variables, including GFR, FENa and u-ENaCγ and increased brachial BP and central BP to a similar extent during both treatments. Vasoactive hormones were changed in the same way by L-NMMA during atorvastatin and placebo treatment. CONCLUSION: During, atorvastatin and placebo treatment, inhibition of nitric oxide synthesis induced the same response in brachial and central blood pressure, GFR, renal tubular function and vasoactive hormones. Thus, the data do not support that atorvastatin changes nitric oxide availability in patients with mild nephropathy. The reduced u-ENaC may reflect changes in sodium absorption in the nephron induced by atorvastatin.

Abnormal increase in urinary aquaporin-2 excretion in response to hypertonic saline in essential hypertension.

BACKGROUND: Dysregulation of the expression/shuttling of the aquaporin-2 water channel (AQP2) and the epithelial sodium channel (ENaC) in renal collecting duct principal cells has been found in animal models of hypertension. We tested whether a similar dysregulation exists in essential hypertension. METHODS: We measured urinary excretion of AQP2 and ENaC ß-subunit corrected for creatinine (u-AQP2(CR), u-ENaC(ß-CR)), prostaglandin E2 (u-PGE2) and cyclic AMP (u-cAMP), fractional sodium excretion (FE(Na)), free water clearance (C(H2O)), as well as plasma concentrations of vasopressin (AVP), renin (PRC), angiotensin II (Ang II), aldosterone (Aldo), and atrial and brain natriuretic peptide (ANP, BNP) in 21 patients with essential hypertension and 20 normotensive controls during 24-h urine collection (baseline), and after hypertonic saline infusion on a 4-day high sodium (HS) diet (300 mmol sodium/day) and a 4-day low sodium (LS) diet (30 mmol sodium/day). RESULTS: At baseline, no differences in u-AQP2(CR) or u-ENaC(ß-CR) were measured between patients and controls. U-AQP2(CR) increased significantly more after saline in patients than controls, whereas u-ENaC(ß-CR) increased similarly. The saline caused exaggerated natriuretic increases in patients during HS intake. Neither baseline levels of u-PGE2, u-cAMP, AVP, PRC, Ang II, Aldo, ANP, and BNP nor changes after saline could explain the abnormal u-AQP2(CR) response. CONCLUSIONS: No differences were found in u-AQP2(CR) and u-ENaC(ß-CR) between patients and controls at baseline. However, in response to saline, u-AQP2(CR) was abnormally increased in patients, whereas the u-ENaC(ß-CR) response was normal. The mechanism behind the abnormal AQP2 regulation is not clarified, but it does not seem to be AVP-dependent. Clinicaltrial.gov identifier: NCT00345124.

Urinary excretion of AQP2 and ENaC in autosomal dominant polycystic kidney disease during basal conditions and after a hypertonic saline infusion.

Renal handling of sodium and water is abnormal in chronic kidney diseases. To study the function and regulation of the aquaporin-2 water channel (AQP2) and the epithelial sodium channel (ENaC) in autosomal dominant polycystic kidney disease (ADPKD), we measured urinary excretion of AQP2 (u-AQP2), the ß-subunit of ENaC (u-ENaC(ß)), cAMP (u-cAMP), and prostaglandin E(2) (u-PGE(2)); free water clearance (C(H2O)); fractional sodium excretion (FE(Na)); and plasma vasopressin (p-AVP), renin (p-Renin), angiotensin II (p-ANG II), aldosterone (p-Aldo), and atrial and brain natriuretic peptide (p-ANP, p-BNP) in patients with ADPKD and healthy controls during 24-h urine collection and after hypertonic saline infusion during high sodium intake (HS; 300 mmol sodium/day) and low sodium intake (LS; 30 mmol sodium/day). No difference in u-AQP2, u-ENaC(ß), u-cAMP, u-PGE(2), C(H2O), and vasoactive hormones was found between patients and controls at baseline, but during HS the patients had higher FE(Na). The saline caused higher increases in FE(Na) in patients than controls during LS, but the changes in u-ENaC(ß), p-Aldo, p-ANP, p-BNP, p-Renin, and p-ANG II were similar. Higher increases in u-AQP2 and p-AVP were seen in patients during both diets. In conclusion, u-AQP2 and u-ENaC(ß) were comparable in patients with ADPKD and controls at baseline. In ADPKD, the larger increase in u-AQP2 and p-AVP in response to saline could reflect an abnormal water absorption in the distal nephron. During LS, the larger increase in FE(Na) in response to saline could reflect a defective renal sodium retaining capacity in ADPKD, unrelated to changes in u-ENaC(ß).

Effect of high and low sodium intake on urinary aquaporin-2 excretion in healthy humans.

The degree of water transport via aquaporin-2 (AQP2) water channels in renal collecting duct principal cells is reflected by the level of the urinary excretion of AQP2 (u-AQP2). In rats, the AQP2 expression varies with sodium intake. In humans, the effect of sodium intake on u-AQP2 and the underlying mechanisms have not previously been studied. We measured the effect of 4 days of high sodium (HS) intake (300 mmol sodium/day; 17.5 g salt/day) and 4 days of low sodium (LS) intake (30 mmol sodium/day; 1.8 g salt/day) on u-AQP2, fractional sodium excretion (FE(Na)), free water clearance (C(H2O)), urinary excretion of PGE(2) (u-PGE(2)) and cAMP (u-cAMP), and plasma concentrations of vasopressin (AVP), renin (PRC), ANG II, aldosterone (Aldo), atrial natriuretic peptide (ANP), and brain natriuretic peptide (BNP) in a randomized, crossover study of 21 healthy subjects, during 24-h urine collection and after hypertonic saline infusion. The 24-h urinary sodium excretion was significantly higher during HS intake (213 vs. 41 mmol/24 h). ANP and BNP were significantly lower and PRC, ANG II, and Aldo were significantly higher during LS intake. AVP, u-cAMP, and u-PGE(2) were similar during HS and LS intake, but u-AQP2 was significantly higher during HS intake. The increases in AVP and u-AQP2 in response to hypertonic saline infusion were similar during HS and LS intake. In conclusion, u-AQP2 was increased during HS intake, indicating that water transport via AQP2 was increased. The effect was mediated by an unknown AVP-independent mechanism.

Effects of dihydralazine on renal water and aquaporin-2 excretion in humans.

OBJECTIVE: Dihydralazine is a vasodilator that lowers blood pressure, but often also leads to significant water and sodium retention. To characterize the effect of dihydralazine on renal sodium and water handling, we tested the hypothesis that dihydralazine causes water retention parallel with an increase in urinary excretion of aquaporin-2 (u-AQP2) in healthy humans. MATERIAL AND METHODS: The effect of intravenous infusion of dihydralazine in three doses (3.125 mg, 6.250 mg and 9.375 mg) on urinary AQP2, water and sodium excretion, heart rate (HR), blood pressure (BP) and vasoactive hormones was measured in a randomized, placebo-controlled, double-blind, crossover study in 17 healthy subjects. Glomerular filtration rate (GFR) and renal tubular function were determined with the continuous infusion clearance technique and vasoactive hormones with radioimmunoassays. RESULTS: Dihydralazine compared to placebo had no impact of u-AQP2 (effect of dihydralazine versus placebo +/-SE) (-0.074+/-0.048 ng/min versus -0.015+/-0.034 ng/min; p = 0.42), despite significant reductions in urine output and free water clearance after 9.375 mg of dihydralazine. Dihydralazine significantly lowered BP and increased HR, plasma levels of angiotensin II and (except after 3.125 mg) atrial natriuretic peptide, while plasma levels of vasopressin, GFR and fractional excretions of sodium and lithium were not significantly changed. CONCLUSIONS: These findings suggest that dihydralazine increases water re-absorption in the distal tubules, independently of vasopressin and of sodium re-absorption. Furthermore, our study does not support an effect of the sympathetic nervous system, the renin-angiotensin system and the natriuretic peptide system on u-AQP2 regulation.

Effects of statins on renal sodium and water handling: acute and short-term effects of atorvastatin on renal haemodynamics, tubular function, vasoactive hormones, blood pressure and pulse rate in healthy, normocholesterolemic humans.

BACKGROUND: Statins have a beneficial effect on cardiovascular morbidity and mortality due to a reduction in plasma cholesterol. However, statins seem to have effects beyond the lowering of plasma cholesterol. We hypothesize that these effects are caused by an effect on renal function. METHODS: We measured the effects of atorvastatin (AS) on renal function in two randomized, placebo-controlled, double-blinded and crossover studies in healthy man. In an acute trial (Study 1), 19 subjects received either 80 mg AS as a single dose or placebo. In a short-term trial (Study 2), 20 subjects received either 80 mg AS or placebo daily for 4 weeks. In both studies glomerular filtration rate (GFR), renal plasma flow (RPF), plasma concentrations of angiotensin II (Ang II), renin (PRC), atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), aldosterone (Aldo), vasopressin (AVP) and blood pressure (BP) were determined. RESULTS: In Study 1 AS decreased fractional excretion of sodium (FE(Na)) significantly (P = 0.035), but very modestly, and reduced diastolic BP (P = 0.024). Apart from this, we found no significant differences in GFR, RPF, tubular function and vasoactive hormones in either Study 1 or 2. CONCLUSIONS: An acute dose of AS decreased FE(Na) and DBP in healthy humans. The reduction in fractional urinary sodium excretion was very modest and transitory, and most likely secondary to the fall in diastolic blood pressure (DBP). However, renal haemodynamics, tubular function, vasoactive hormones and blood pressure were unchanged during short-term statin treatment in healthy man.

Down-regulation of urinary AQP2 and unaffected response to hypertonic saline after 24 hours of fasting in humans.

BACKGROUND: In rats, 24 hours of fasting impairs urinary concentrating ability by down-regulation of aquaporin-2 (AQP2). We tested the hypothesis that 24 hours of fasting in humans reduces the capability to form AQP2 and impairs the antidiuretic response to hypertonic saline infusion. METHODS: In a crossover study of 14 healthy subjects, the effect of 24 hours of fasting was compared to a nonfasting control experiment on urinary excretion of AQP2 (u-AQP2), free water clearance (C(H(2)O)), plasma arginine vasopressin (AVP), urinary cyclic AMP (u-cAMP), and natriuretic peptides. The following response to 3% sodium infusion was measured using the same effect variables. U-AQP2, AVP, and u-cAMP were determined by radioimmunoassays. RESULTS: Fasting during 24 hours reduced u-AQP2 (14%), increased AVP (30%) despite a reduction in serum osmolality (P < 0.05), and depleted volume. C(H(2)O) and urine volume were not reduced, thus relatively increased after fasting. u-cAMP was not significantly different between the two procedures. Three percent saline resulted in the same relative increases in AVP, serum osmolality, u-AQP2, and u-cAMP and decreases in C(H(2)O) and urine volume independently of fasting. The reduced u-AQP2 and increased AVP after fasting were maintained during and after saline infusion. CONCLUSION: Twenty-four hours of fasting decreased u-AQP2 and reduced urine osmolality likely as a result of decreased sensitivity of collecting duct cells to AVP. Fasting-related insensitivity of collecting duct cells to AVP was restored by 3% saline infusion. Finally, after saline infusion, other factors such as the increased plasma atrial natriuretic peptide (p-ANP) levels could contribute to the u-AQP2 regulation.