Feasibility of measuring renal blood flow by phase-contrast magnetic resonance imaging in patients with autosomal dominant polycystic kidney disease.

OBJECTIVES: Renal blood flow (RBF) has been shown to predict disease progression in autosomal dominant polycystic kidney disease (ADPKD). We investigated the feasibility and accuracy of phase-contrast RBF by MRI (RBFMRI) in ADPKD patients with a wide range of estimated glomerular filtration rate (eGFR) values. METHODS: First, we validated RBFMRI measurement using phantoms simulating renal artery hemodynamics. Thereafter, we investigated in a test-set of 21 patients intra- and inter-observer coefficient of variation of RBFMRI. After validation, we measured RBFMRI in a cohort of 91 patients and compared the variability explained by characteristics indicative for disease severity for RBFMRI and RBF measured by continuous hippuran infusion. RESULTS: The correlation in flow measurement using phantoms by phase-contrast MRI was high and fluid collection was high (CCC=0.969). Technical problems that precluded RBFMRI measurement occurred predominantly in patients with a lower eGFR (34% vs. 16%). In subjects with higher eGFRs, variability in RBF explained by disease characteristics was similar for RBFMRI compared to RBFHip, whereas in subjects with lower eGFRs, this was significantly less for RBFMRI. CONCLUSIONS: Our study shows that RBF can be measured accurately in ADPKD patients by phase-contrast, but this technique may be less feasible in subjects with a lower eGFR. KEY POINTS: Renal blood flow (RBF) can be accurately measured by phase-contrast MRI in ADPKD patients. RBF measured by phase-contrast is associated with ADPKD disease severity. RBF measurement by phase-contrast MRI may be less feasible in patients with an impaired eGFR.

Copeptin, a surrogate marker for arginine vasopressin, is associated with declining glomerular filtration in patients with diabetes mellitus (ZODIAC-33).

AIM/HYPOTHESIS: Arginine vasopressin (AVP), the hormone important for maintaining fluid balance, has been shown to cause kidney damage in rodent models of diabetes. We investigated the potential role of AVP in the natural course of kidney function decline in diabetes in an epidemiological study. METHODS: Plasma copeptin, a surrogate for AVP, was measured in baseline samples from patients with type 2 diabetes treated in primary care and included in the Zwolle Outpatient Diabetes project Integrating Available Care (ZODIAC) cohort. RESULTS: Samples from 1,328 patients were available; 349 were analysed separately because they used renin-angiotensin-aldosterone system inhibition (RAASi), which influences albumin/creatinine ratio (ACR) and estimated (e)GFR. In the other 979 patients (46% men, age 68 years [58-75], ACR 1.8 mg/mmol [0.9-5.7], eGFR 67 ± 14 ml min(-1) 1.73 m(-2)) baseline copeptin (5.3 pmol/l [3.2-9.5]) was significantly associated with log e [ACR] and eGFR, even after adjustment for sex, age and risk factors for kidney function decline (standardised [std] ß 0.13, p < 0.001, std ß -0.20, p < 0.001 respectively). Follow-up data were available for 756 patients (6.5 years [4.1-9.6]). Baseline copeptin was associated with increase in ACR (std ß 0.09, p = 0.02), but lost significance after adjustment (std ß 0.07, p = 0.08). Copeptin was associated with a decrease in eGFR after adjustment (std ß -0.09, p = 0.03). The strength of the association of copeptin with change in eGFR was stronger than that of established risk factors for kidney function decline (e.g. BMI, HbA1c). In patients who used RAASi there was a significant association between baseline copeptin and ACR and eGFR, but not with change in ACR and eGFR. CONCLUSIONS/INTERPRETATION: In patients with diabetes not using RAASi a higher baseline copeptin concentration is significantly associated with higher baseline ACR and lower eGFR values and with a decline in eGFR during follow-up. This last association is independent of, and stronger than, most traditional risk factors for kidney function decline.

Potential deleterious effects of vasopressin in chronic kidney disease and particularly autosomal dominant polycystic kidney disease.

The antidiuretic hormone vasopressin is crucial for regulating free water clearance in normal physiology. However, it has also been hypothesized that vasopressin has deleterious effects on the kidney. Vasopressin is elevated in animals and patients with chronic kidney disease. Suppression of vasopressin activity reduces proteinuria, renal hypertrophy, glomerulosclerosis and tubulointerstitial fibrosis in animal models. The potential detrimental influence of vasopressin is probably mediated by its effects on mesangial cell proliferation, renin secretion, renal hemodynamics, and blood pressure. In this review, we discuss the increasing body of evidence pointing towards the contribution of vasopressin to chronic kidney disease progression in general and to autosomal dominant polycystic kidney disease in particular. These data allude to the possibility that interventions directed at lowering vasopressin activity, for example by the administration of vasopressin receptor antagonists or by drinking more water, may be beneficial in chronic kidney disease.