Renal water and sodium handling during gradated unilateral ureter obstruction

What is the utility of urodynamics, including ambulatory, and 24 h monitoring, in predicting upper urinary tract damage in neuro-urological patients and other lower urinary tract dysfunction? ICI-RS 2017

AIMS

This article focuses on how, and if, urodynamics can help to identify which kidneys are in danger of deteriorating in function and also gives recommendations for future research.

METHODS

At the International Consultation on Incontinence-Research Society (ICI-RS) in 2017, a multi-disciplinary group presented a literature search of what is known about the utility of Urodynamics, including ambulatory, and 24 h monitoring, in predicting upper urinary tract damage in neuro-urological patients and other lower urinary tract dysfunctions. Wider discussions regarding knowledge gaps, and ideas for future research ensued and are presented in this paper along with a review of the evidence.

RESULTS

The current treatment strategy both in congenital and acquired neurogenic bladder is rather aggressive and successful when addressing hazards to kidney function. This article has highlighted uncertainties concerning the use of 40 cmH2O DLPP and even the lower value of 20. The current literature suggests that patients with spina bifida and those with spinal cord injury have a higher risk of developing upper urinary tract damage and kidney function impairment than those with multiple sclerosis.

CONCLUSIONS

Future research should focus on less invasive methods to assess the risk to the upper and lower urinary tract such as urine and serum measurements of cytokines that are involved in the pathophysiology of urinary tract impairment.

The physical basis of renal fibrosis: effects of altered hydrodynamic forces on kidney homeostasis

Healthy kidneys are continuously exposed to an array of physical forces as they filter the blood: shear stress along the inner lumen of the tubules, distension of the tubular walls in response to changing fluid pressures, and bending moments along both the cilia and microvilli of individual epithelial cells that comprise the tubules. Dysregulation of kidney homeostasis via underlying medical conditions such as hypertension, diabetes, or glomerulonephritis fundamentally elevates the magnitudes of each principle force in the kidney and leads to fibrotic scarring and eventual loss of organ function. The purpose of this review is to summarize the progress made characterizing the response of kidney cells to pathological levels of mechanical stimuli. In particular, we examine important, mechanically responsive signaling cascades and explore fundamental changes in renal cell homeostasis after cyclic strain or fluid shear stress exposure. Elucidating the effects of these disease-related mechanical imbalances on endogenous signaling events in kidney cells presents a unique opportunity to better understand the fibrotic process.

Regional changes in renal cortical glucose, lactate and urea during acute unilateral ureteral obstruction

OBJECTIVE

Acute unilateral ureteral obstruction (UUO) leads to changes in kidney function and metabolism. Microdialysis offers the possibility of topical analysis of changes in kidney metabolism. We applied microdialysis to the porcine kidney and evaluated its impact on gross kidney function. Furthermore, we investigated regional variations in renal interstitial fluid (RIF) glucose, lactate and urea during acute UUO.

MATERIAL AND METHODS

Eight anesthetized pigs were used. Microdialysis probes were inserted in the upper, middle and lower thirds of the left renal cortex and perfused with Ringer's chloride at a rate of 0.3 microl/min. Dialysates were fractionated for 30-min periods. Bilateral intrapelvic pressure, urinary output, urinary osmolality, the excretion fractions of sodium and potassium, renal blood flow and the glomerular filtration rate were measured. Subsequently, left-sided graded ureteral obstruction was initiated, using the kidney's own urine production as a counter-pressure.

RESULTS

The application of three microdialysis probes did not have any impact on kidney function. Ureteral obstruction decreased RIF glucose in the upper and lower thirds of the kidney, but not in the middle third. RIF lactate did not change. Interstitial urea increased in all regions of the kidney, but most markedly in the upper and lower poles.

CONCLUSIONS

Microdialysis is of potential value for assessing the renal interstitial milieu under different pathophysiological conditions. Ureteral obstruction resulted in regional differences in cortical metabolites, predominantly affecting the upper and lower poles.

Investigating the role of ischemia vs. elevated hydrostatic pressure associated with acute obstructive uropathy

Obstructive uropathy can cause irreversible renal damage. It has been hypothesized that elevated hydrostatic pressure within renal tubules and/or renal ischemia contributes to cellular injury following obstruction. However, these assaults are essentially impossible to isolate in vivo. Therefore, we developed a novel pressure system to evaluate the isolated and coordinated effects of elevated hydrostatic pressure and ischemic insults on renal cells in vitro. Cells were subjected to: (1) elevated hydrostatic pressure (80 cm H(2)O); (2) ischemic insults (hypoxia (0% O(2)), hypercapnia (20% CO(2)), and 0 mM glucose media); and (3) elevated pressure + ischemic insults. Cellular responses including cell density, lactate dehydrogenase (LDH) release, and intracellular LDH (LDH(i)), were recorded after 24 h of insult and following recovery. Data were analyzed to assess the primary effects of ischemic insults and elevated pressure. Unlike pressure, ischemic insults exerted a primary effect on nearly all response measurements. We also evaluated the data for insult interactions and identified significant interactions between ischemic insults and pressure. Altogether, findings indicate that pressure may sub-lethally effect cells and alter cellular metabolism (LDH(i)) and membrane properties. Results suggest that renal ischemia may be the primary, but not the sole, cause of cellular injury induced by obstructive uropathy.

Implications of oxidative stress in the pathophysiology of obstructive uropathy

Although the functional and clinical alterations occurring in patients with obstructive uropathy are not well understood, it has been suggested that oxidative stress could contribute in the mechanism responsible for the impairment of sodium and water balance. This study aimed to test the hypothesis that red wine administration causes an amelioration of both the renal damage and impairment of renal Na(+), K(+)-ATPase activity occurring after ureteral obstruction in the rat. Twenty-four male Wistar adult rats weighting 200-250 g were used. Half of them received a 10-week treatment with wine as the sole fluid source, while the other group received water. Both groups were subjected to 24-h unilateral ureteral obstruction (UUO). Kidney tissue was collected following the relief of the ligature to perform the biochemical assessments. Urine and blood samples were taken at baseline and after the relief. Results show that the treatment with red wine significantly enhances the activity of antioxidant enzymes, and thus reduces renal lipid peroxidation secondary to UUO, which correlated negatively with Na(+), K(+)-ATPase activity. Based on this and other previous data, it could be suggested that red wine administration may prevent renal damage secondary to UUO by inducing enhanced antioxidant potential.

Exploring mechanisms involved in renal tubular sensing of mechanical stretch following ureteric obstruction

Tubular mechanical stretch is the key primary insult in obstructive nephropathy. This review addresses how the renal tubular epithelium senses and responds to mechanical stretch. Using data from renal and nonrenal systems, we describe how sensing of stretch initially occurs via the activation of ion channels and subsequent increases in intracellular calcium levels. Calcium influxes activate a number of adaptive and proinjury responses. Key among these are 1) the activation of Rho, consequent cytoskeletal rearrangements, and downstream increases in focal adhesion assembly; and 2) phospholipase activation and resultant mitogen-activated protein kinase activation. These early signaling events culminate in adaptive cellular coupling to the extracellular matrix, a process termed the cell strengthening response. Direct links can be made between increased expression of genes involved in the development of obstructive nephropathy and initial sensing of mechanical stretch. The review illustrates the repercussions of mechanical stretch as a renal stress stimulus, specific to ureteric obstruction, and provides an insight into how tubular responses to mechanical stretch are ultimately implicated in the development of obstructive nephropathy.

Cell biological aspects of the vasopressin type-2 receptor and aquaporin 2 water channel in nephrogenic diabetes insipidus

In the renal collecting duct, water reabsorption is regulated by the antidiuretic hormone vasopressin (AVP). Binding of this hormone to the vasopressin V2 receptor (V2R) leads to insertion of aquaporin-2 (AQP2) water channels in the apical membrane, thereby allowing water reabsorption from the pro-urine to the interstitium. The disorder nephrogenic diabetes insipidus (NDI) is characterized by the kidney's inability to concentrate pro-urine in response to AVP, which is mostly acquired due to electrolyte disturbances or lithium therapy. Alternatively, NDI is inherited in an X-linked or autosomal fashion due to mutations in the genes encoding V2R or AQP2, respectively. This review describes the current knowledge of the cell biological causes of NDI and how these defects may explain the patients' phenotypes. Also, the increased understanding of these cellular defects in NDI has opened exciting initiatives in the development of novel therapies for NDI, which are extensively discussed in this review.