Renal haemodynamics and prostaglandin synthesis in partial unilateral ureteric obstruction

Kidney computed tomography perfusion in patients with ureteral obstruction

INTRODUCTION

Kidney perfusion on CT is an encouraging surrogate for renal scintigraphy in assessing renal function. However, data on dynamic volumetric CT in patients with kidney obstruction is lacking. Thus, the aim of this study is to determine the feasibility of CT-based renal perfusion using a dynamic volume to assess renal hemodynamics at different degrees and durations of obstruction.

MATERIALS AND METHODS

We included patients with unilateral kidney obstruction in our single-center, prospective study. The patients were divided into three groups. Patients without dilatation of the pelvicalyceal system (PCS) and normal parenchyma thickness were included into Group 1; patients with PCS dilatation and parenchyma thickness 1.8-2.4 cm-into Group 2; and patients with ureteropyelocalicoectasia and parenchyma thickness less than 1.8 cm-into Group 3.

RESULTS

Total of 56 patients were enrolled. In Group 1 mean values of cortical and medullar arterial blood flow, blood volume, and extraction fraction were within the normal range. Changes in contralateral kidney were not determined. Patients from Group 2 showed significant differences in blood flow parameters in the cortical and medulla of the obstructed kidney. No changes in perfusion values in the contralateral kidney was observed. In patients from Group 3 there was a marked decrease in perfusion on the side of obstruction compared to Group 2, indicating that the degree of expansion of the PCS directly correlates with the change in blood flow. However, in the contralateral kidney, these indicators exceeded the normal values of perfusion.

CONCLUSION

CT perfusion allows to objectively assess changes in blood flow in the setting of renal obstruction. The degree of obstruction directly affects the measured rate of blood flow.

Assessment of renal function in patients with unilateral ureteral obstruction using whole-organ perfusion imaging with 320-detector row computed tomography

Background

Obstructed nephropathy is a common complication of several disease processes. Accurate evaluation of the functional status of the obstructed kidney is important to achieve a good outcome. The purpose of this study was to investigate renal cortical and medullary perfusion changes associated with unilateral ureteral obstruction (UUO) using whole-organ perfusion imaging with 320-detector row computed tomography (CT).

Methodology/Principle Findings

Sixty-four patients with UUO underwent whole-organ CT perfusion imaging. Patients were divided into 3 groups, mild, moderate, and severe, based on hydronephrosis severity. Twenty sex- and age-matched patients without renal disease, who referred to abdominal CT, were chosen as control subjects. Mean cortical and medullary perfusion parameters of obstructed and contralateral kidneys were compared, and mean perfusion ratios between obstructed and contralateral kidneys were calculated and compared. Mean cortical or medullary blood flow (BF) and blood volume (BV) of the obstructed kidneys in the moderate UUO and BF, BV, and clearance (CL) in the severe UUO were significantly lower than those of the contralateral kidneys (p < 0.05). The mean cortical or medullary BF of the obstructed kidney in the moderate UUO, and BF, BV, and CL in the severe UUO were significantly lower than those of the kidneys in control subjects (p < 0.05). Mean cortical or medullary BF of the non-obstructed kidneys in the severe UUO were statistically greater than that of normal kidneys in control subjects (p < 0.05). An inverse correlation was observed between cortical and medullary perfusion ratios and grades of hydronephosis (p < 0.01).

Conclusions/Significance

Perfusion measurements of the whole kidney can be obtained with 320-detector row CT, and estimated perfusion ratios have potential for quantitatively evaluating UUO renal injury grades.

Functional evaluation of transplanted kidneys using arterial spin labeling MRI

PURPOSE

To investigate non-contrast-enhanced arterial spin labeling (ASL) MRI for functional assessment of transplanted kidneys at 1.5 Tesla (T) and 3T.

MATERIALS AND METHODS

This study was approved by the local ethics committee, and written informed consent was obtained from all participants. Ninety eight renal allograft recipients (mean age, 51.5 ± 14.6 years) were prospectively included in this study. ASL MRI was performed at 1.5T (n = 65) and 3T (n = 33) using a single-slice flow-sensitive alternating inversion recovery true-fast imaging with steady-state precession (FAIR True-FISP) sequence in the paracoronal plane. ASL perfusion was regional analyzed for the renal cortex on parameter maps. ASL was compared between patients with good or moderate allograft function (Group a; estimated glomerular filtration rate [eGFR] > 30 mL/min/1.73 m(2)) and patients with heavily impaired allograft function (Group b; eGFR ≤ 30 mL/min/1.73 m(2)) and correlated to renal function as determined by eGFR.

RESULTS

ASL perfusion and eGFR were comparable at 1.5T (246.9 ± 66.8 mL/100 g/min and 41.9 ± 22.7 mL/min/1.73 m(2)) and 3T (236.5 ± 102.3 mL/100 g/min and 35.9 ± 22.9 mL/min/1.73 m(2)). ASL perfusion was significantly higher in group a (282.7 ± 60.8 mL/100 g/min) as compared to group b (178.2 ± 63.3 mL/100 g/min) (P < 0.0001). ASL perfusion values exhibited a significant correlation with renal function as determined by eGFR (r = 0.59; P < 0.0001).

CONCLUSION

Cortical ASL perfusion values differ between patients with good or moderate allograft function and poor allograft function and correlate significantly with allograft function. Our results highlight the potential of ASL MRI for functional evaluation of renal allografts.

[Blood oxygenation level dependent (BOLD)--renal imaging: concepts and applications]

Many renal diseases as well as several pharmacons cause a change in renal blood flow and/or renal oxygenation. The blood oxygenation level dependent (BOLD) imaging takes advantage of local field inhomogeneities and is based on a T2*-weighted sequence. BOLD is a non-invasive method allowing an estimation of the renal, particularly the medullary oxygenation, and an indirect measurement of blood flow without administration of contrast agents. Thus, effects of different drugs on the kidney and various renal diseases can be controlled and observed. This work will provide an overview of the studies carried out so far and identify ways how BOLD can be used in clinical studies.

Quantification of renal allograft perfusion using arterial spin labeling MRI: initial results

OBJECTIVE

To quantify renal allograft perfusion in recipients with stable allograft function and acute decrease in allograft function using nonenhanced flow-sensitive alternating inversion recovery (FAIR)-TrueFISP arterial spin labeling (ASL) MR imaging.

METHODS

Following approval of the local ethics committee, 20 renal allograft recipients were included in this study. ASL perfusion measurement and an anatomical T2-weighted single-shot fast spin-echo (HASTE) sequence were performed on a 1.5-T scanner (Magnetom Avanto, Siemens, Erlangen, Germany). T2-weighted MR urography was performed in patients with suspected ureteral obstruction. Patients were assigned to three groups: group a, 6 patients with stable allograft function over the previous 4 months; group b, 7 patients with good allograft function who underwent transplantation during the previous 3 weeks; group c, 7 allograft recipients with an acute deterioration of renal function.

RESULTS

Mean cortical perfusion values were 304.8 +/- 34.4, 296.5 +/- 44.1, and 181.9 +/- 53.4 mg/100 ml/min for groups a, b and c, respectively. Reduction in cortical perfusion in group c was statistically significant.

CONCLUSION

Our results indicate that ASL is a promising technique for nonenhanced quantification of cortical perfusion of renal allografts. Further studies are required to determine the clinical value of ASL for monitoring renal allograft recipients.

Evaluation of shockwave lithotripsy induced renal damage using heat shock protein 70 expression in the presence of different urinary obstruction periods

PURPOSE

The aim of this study was to investigate the deleterious effects of shockwaves (SWs) using heat shock protein (HSP) 70 expression on obstructed kidneys with different obstruction periods.

MATERIALS AND METHODS

Twenty-five rabbits were divided into two groups with 11 rabbits in each group. Both kidneys of the remaining three rabbits served as a sham group. All animals underwent right ureteral ligation using surgical clips. In group 1 (n = 6), 1500 SWs were applied to the obstructed kidney after 3 days of ligation, and the kidneys were removed on day 4. Group 1 control (n = 5) animals also underwent nephrectomy on day 4 without receiving SWs. Group 2 (n = 6) animals received the same dose of SWs after 6 days of ureteral ligation and were nephrectomized on day 7. Group 2 control (n = 5) animals did not receive SWs and were nephrectomized on day 7. Immunohistochemical staining was performed for HSP70 expression, and staining intensity was graded semiquantatively.

RESULTS

HSP70 staining results were significantly lower in the sham group compared with results in the study groups. Immunostaining was significantly higher in the cortical collector tubuli in group 1 than group 1 control (P = 0.006). No significant difference was detected in group 2 compared with group 2 control. In the medullar cortical tubuli, HSP70 staining was significantly higher in group 1 than group 1 control (P = 0.03). It was also higher in group 2 than group 2 control (P = 0.04). The mean HSP70 glomerular staining scores were not statistically significant between each group.

CONCLUSION

Application of SWs in the presence of obstruction has deleterious effects on the kidney tissue.

Renal Doppler Ultrasound Examination of Ureteral Obstruction in Rabbits:

RATIONALE AND OBJECTIVES

We sought to investigate the usefulness of Doppler resistive index (RI) in the diagnosis and follow-up of obstructive uropathy of different degrees and different sites of obstruction.

METHODS

Forty-six rabbits were classified as follows: group I, partial unilateral obstruction of the proximal ureter (n = 16); group II, complete unilateral obstruction of the proximal ureter (n = 17); group III, complete unilateral obstruction of the distal ureter (n = 13). The RI of the obstructed and contralateral kidneys was measured preoperatively and postoperatively 1 hour, 6 hours, 1 day, 3 days, 1 week, 2 weeks, and 4 weeks, respectively. In each group, the RI was analyzed for statistical differences in the preoperative versus postoperative kidneys, and the obstructed versus contralateral kidneys. We also analyzed the statistical differences in RIs of the obstructed kidneys, in interrenal RI differences (DeltaRI: RI of the obstructed kidney - RI of the contralateral kidney), and in RI ratio (RI of the obstructed kidney / RI of the contralateral kidney) between the 3 groups.

RESULTS

The RIs in the obstructed versus contralateral kidneys were significantly increased (P < 0.05) postoperatively at 1 hour, 1 day, and 2 weeks in group I; 6 hours and 1 week in group II; and 1 hour, 6 hours, and 3 days in group III. In obstructed kidneys, the RIs in the postoperative versus preoperative kidneys were significantly increased (P < 0.05) from 1 hour to 2 weeks in group I and from 1 hour to 4 weeks in group II. There were no statistically significant differences in mean RI, DeltaRI, and RI ratio between the 3 groups during the preoperative and postoperative period.

CONCLUSIONS

Doppler RI can be elevated in hydronephrotic kidney as a result of both partial and complete obstruction of the ureter. There are no RI differences among obstructed kidneys with different degree and different site of ureteral obstruction.

Increased nephron volume is not a cause of supranormal renographic differential renal function in patients with ureteropelvic junction obstruction

PURPOSE

Increasing clinical importance is being placed on the role of differential renal function (DRF) in the management of congenital ureteropelvic junction obstruction. Supranormal DRF of the hydronephrotic kidney on renal scan is a puzzling phenomenon and is hypothesized to be due to an increase in single nephron filtration or nephron volume without sound evidence. We studied the histopathological changes of hydronephrotic kidneys to determine whether glomerular hypertrophy underlies supranormal DRF.

MATERIALS AND METHODS

We retrospectively evaluated the records of 3 females and 32 males with unilateral congenital hydronephrosis who underwent pyeloplasty. Mean patient age at operation was 12.6 months (range 0.1 to 144). Needle biopsies from 3 different sites at the lower pole of the kidney were performed during surgery. To evaluate the presence of glomerular hypertrophy, the maximal planar area of glomeruli was measured under light microscopy using an image analyzer. Tissue samples obtained from kidneys without a history of urinary tract disease at autopsy were used as controls. The mean glomerular areas of the patient and control groups were evaluated according to DRF and age.

RESULTS

The mean glomerular area values of the patient group were smaller than those of the control group, except for 4 patients. The glomerular areas of the hydronephrotic kidneys with supranormal DRF were not significantly different from those of the control group. Instead, the probability of larger renal glomeruli increased with decreasing DRF (p = 0.1155).

CONCLUSIONS

Increased nephron volume can be discounted as a cause of supranormal DRF.

Mechanical deformation induced apoptosis in human proximal renal tubular epithelial cells is caspase dependent

PURPOSE

Ureteral obstruction (UO) results in apoptosis of renal tubular epithelial cells. We postulated that mechanical deformation and inflammation contribute to the cellular loss that occurs as a result of UO and it is mediated through altered heat shock protein 70 (HSP-70) expression and the caspase cascade.

MATERIALS AND METHODS

Human HK-2 renal tubular cells were subjected to mechanical stretch. Cell viability and apoptosis were assessed by flow cytometry; HSP-70 and caspase 3 protein expression by Western blotting, and caspase 3 activity by fluorescence substrates.

RESULTS

Mechanical stretch caused direct apoptosis induction and it also primed for tumor necrosis factor-alpha induced apoptosis, which was caspase 3 dependent. Although HSP-70 protein expression was increased during mechanical stretch, the protective effects of HSP-70 were only seen after further induction by heat shocking.

CONCLUSIONS

Altering HSP-70 expression and manipulating the caspase cell death proteases represent a novel pathway to protect against renal tubular cell apoptosis and the potential for progression to renal failure in UO.

Cytoprotective effects of nitrates in a cellular model of hydronephrosis

BACKGROUND

The earliest insult to the kidney following the onset of ureteral obstruction is a marked elevation in collecting system pressure. This imparts a mechanical stress that is transmitted directly from the collecting system to the kidney substance. Renal tubular injury is the principal functional and histological change encountered, with glomerular changes being less marked and occurring later. Nitric oxide (NO) has been shown to protect against renal injury in UO, but its mode of action has not been clearly defined.

METHODS

MDCK (canine) and HK-2 (human) renal tubular cells were grown under control conditions or subjected to mechanical strain for periods of 24 and 48 hours. Cells were studied treated with or without Fas-antibody, etoposide or diethyl maleate (DEM) alone or in combination with NG-monomethyl l-arginine (L-NMMA), sodium nitroprusside (SNP) or l-arginine. Cell proliferation and apoptosis was determined using propidium iodide DNA staining. NO production and inducible NO synthase (iNOS) expression were measured by the Griess reaction and Western blotting, respectively.

RESULTS

Cells subjected to mechanical strain displayed a decrease in the proportion of cells undergoing cell division. They also showed an increased susceptibility to apoptosis. Associated with this was a decrease in Bcl-2 expression. An increase in iNOS expression was seen in cells subjected to mechanical strain, but no increase in NO production. The cellular effects of mechanical strain were reversed by SNP and l-arginine.

CONCLUSIONS

Culture of renal tubule cells in an environment of mechanical strain results in an imbalance in homeostasis and a net cell loss. This can be reversed by the administration of an NO donor or precursor.

Effect of thromboxane and nitric oxide blockade on renal blood flow increase during volume expansion in hydronephrotic rats

OBJECTIVE

It has recently been found that hydronephrotic rats, despite low diuresis, show a significant increase in renal blood flow (RBF) during volume expansion. The present experiments were designed to evaluate the mechanisms underlying this phenomenon.

MATERIAL AND METHODS

Three-week-old Sprague-Dawley rats underwent partial obstruction of the left ureter using the Ulm-Miller psoas groove technique. The effects on RBF were studied 3 weeks later under general anesthesia using real-time ultrasound flowmetry, first during normohydration and then during extracellular volume expansion, in both untreated animals, and after prior blockade of either thromboxane or nitric oxide.

RESULTS

Significant hydronephrosis developed in all cases. RBF was normal under control conditions. During volume expansion RBF increased significantly in untreated experimental animals (mean 7.5%). In contrast to this finding, RBF remained unchanged during volume expansion in both the thromboxane and nitric oxide blockade groups.

CONCLUSION

It is concluded that a thromboxane- and/or nitric oxide-dependent RBF redistribution takes place in hydronephrotic kidneys during volume expansion.

Nitric oxide in unilateral ureteral obstruction: effect on regional renal blood flow

BACKGROUND

Ureteral obstruction (UO) is characterized by reduced blood flow and loss of tissue mass in the involved kidney(s). Vasoactive mediators interact to produce an initial hyperemia, followed by a sustained decrease in renal blood flow in the obstructed kidney. Nitric oxide (NO) has been shown to play a central role in the acute hyperemic response to UO. Its role in the reduced perfusion of prolonged UO is less studied.

METHODS

Ureteral obstruction was achieved by ligation of the distal left ureter and maintained for 24 hours. Blood flow was studied in untreated animals and after the administration of the NO synthase (NOS) inhibitor N-mono-methyl L-arginine and the NO donor sodium nitroprusside. Tissue was collected for localization and quantitation of NOS. Serum and renal tissue L-arginine levels were measured in control and UO settings.

RESULTS

Blood flow in the obstructed kidney diminished to approximately 50% of control values after 24 hours of UO. NOS blockade led to a further decrease in blood flow. Supplementation with exogenous nitrates restored renal blood flow to levels approaching control values. Serum and tissue L-arginine levels did not change with UO. NOS expression was seen to increase with increasing duration of obstruction, with staining most pronounced in the renal tubules.

CONCLUSIONS

NO plays a vasodilatory role even in the hypoperfusion of prolonged UO. The administration of exogenous nitrates has a restorative effect on blood flow, suggesting therapeutic potential in UO.

Renal hemodynamic changes after complete and partial unilateral ureteral obstruction in the fetal lamb

PURPOSE

Complete and partial ureteral obstruction decreases ipsilateral renal blood flow in neonatal and adult animals. However, the effects of obstruction that develops during gestation may be different from those in neonatal or adult animals. We determine whether complete or partial ureteral obstruction decreases ipsilateral renal blood flow in fetal sheep.

MATERIALS AND METHODS

We positioned an ultrasonic flow transducer around both renal arteries in 21 fetal sheep at 123 to 125 days of gestation. Unilateral ureteral obstruction was created in 16 fetuses, including complete and partial obstruction in 7 and 9, respectively. There were 5 controls. Renal blood flow and arterial blood pressure were measured daily for a minimum of 7 days.

RESULTS

All obstructed kidneys had hydronephrosis, partially obstructed kidneys had less obstruction and contralateral kidneys had none. Renal weight was similar in obstructed and contralateral kidneys in the sham operated, partial and complete obstruction groups. After partial ureteral obstruction renal blood flow in obstructed and contralateral kidneys was increased compared to that in sham operated kidneys up to 11 days after obstruction was created. After complete ureteral obstruction the blood flow in obstructed kidneys was significantly lower than in the unobstructed counterparts but it remained 124% of initial renal blood flow at 10 days. Elevated ureteral pressure was maintained in obstructed kidneys throughout the study period.

CONCLUSIONS

In our experiment partial ureteral obstruction in the fetus did not decrease renal blood flow to the ipsilateral kidney even after 7 days. Complete obstruction decreased blood flow in the affected kidney but not to same magnitude as that in previous adult animal studies. Our findings suggest that during gestation renal blood flow is maintained in the presence of obstruction.