Changes in renal blood flow after surgically induced weight loss: can bariatric surgery halt the progression of chronic kidney disease?

BACKGROUND

We previously demonstrated how kidney injury in patients with morbid obesity can be reversed by bariatric surgery (BaS).

OBJECTIVE(S)

Based on previous experience, we hypothesize patients' potentially reversible kidney injury might be secondary to reduction in renal blood flow (RBF), which improves following BaS.

SETTING

Academic Hospital.

METHODS

We conducted a retrospective analysis of patients who underwent BaS at our institution from 2002 to 2019. We identified patients with chronic kidney disease (CKD) using the estimated glomerular filtration rate (eGFR) from the CKD Epidemiology Collaboration Study (CKD-EPI) classification system. We used the BUN/Creatinine (Cr) ratio pre- and postoperatively to determine a prerenal (decreased RBF) versus intrinsic component as the responsible cause of CKD in this patient population. Decreased RBF was defined as BUN/Cr > 20 preoperatively.

RESULTS

Our analysis included n = 2924 patients, of which 11% (n = 325) presented decreased RBF. From our original sample, only n = 228 patients had the complete data necessary to assess both eGFR and RBF (BUN/Cr). Patients with baseline CKD stage 2 demonstrated preoperative BUN/Cr 20.85 ± 10.23 decreasing to 14.99 ± 9.10 at 12-month follow-up (P < .01). Patients with baseline CKD stage 3 presented with preoperative BUN/Cr 23.88 ± 8.75; after 12-month follow-up, BUN/Cr ratio decreased to 16.38 ± 9.27 (P < .01). Patients with CKD stage 4 and ESRD (eGFR < 30) did not demonstrate a difference for pre- and postoperative BUN/Cr 21.71 ± 9.28 and 19.21 ± 14.58, respectively.

CONCLUSION(S)

According to our findings, patients with CKD stages 1-3 present improvement of their kidney function after BaS. This amelioration could be secondary to improvement of the RBF, an unstudied reversible mechanism of kidney injury in the bariatric population.

Renal sympathetic denervation improves pressure-natriuresis relationship in cardiorenal syndrome: insight from studies with Ren-2 transgenic hypertensive rats with volume overload induced using aorto-caval fistula

The aim was to evaluate the effects of renal denervation (RDN) on autoregulation of renal hemodynamics and the pressure-natriuresis relationship in Ren-2 transgenic rats (TGR) with aorto-caval fistula (ACF)-induced heart failure (HF). RDN was performed one week after creation of ACF or sham-operation. Animals were prepared for evaluation of autoregulatory capacity of renal blood flow (RBF) and glomerular filtration rate (GFR), and of the pressure-natriuresis characteristics after stepwise changes in renal arterial pressure (RAP) induced by aortic clamping. Their basal values of blood pressure and renal function were significantly lower than with innervated sham-operated TGR (p < 0.05 in all cases): mean arterial pressure (MAP) (115 ± 2 vs. 160 ± 3 mmHg), RBF (6.91 ± 0.33 vs. 10.87 ± 0.38 ml.min-1.g-1), urine flow (UF) (11.3 ± 1.79 vs. 43.17 ± 3.24 µl.min-1.g-1) and absolute sodium excretion (UNaV) (1.08 ± 0.27 vs, 6.38 ± 0.76 µmol.min-1.g-1). After denervation ACF TGR showed improved autoregulation of RBF: at lowest RAP level (80 mmHg) the value was higher than in innervated ACF TGR (6.92 ± 0.26 vs. 4.54 ± 0.22 ml.min-1.g-1, p < 0.05). Also, the pressure-natriuresis relationship was markedly improved after RDN: at the RAP of 80 mmHg UF equaled 4.31 ± 0.99 vs. 0.26 ± 0.09 µl.min-1.g-1 recorded in innervated ACF TGR, UNaV was 0.31 ± 0.05 vs. 0.04 ± 0.01 µmol min-1.g-1 (p < 0.05 in all cases). In conclusion, in our model of hypertensive rat with ACF-induced HF, RDN improved autoregulatory capacity of RBF and the pressure-natriuresis relationship when measured at the stage of HF decompensation.

Physiological confounders of renal blood flow measurement

OBJECTIVES

Renal blood flow (RBF) is controlled by a number of physiological factors that can contribute to the variability of its measurement. The purpose of this review is to assess the changes in RBF in response to a wide range of physiological confounders and derive practical recommendations on patient preparation and interpretation of RBF measurements with MRI.

METHODS

A comprehensive search was conducted to include articles reporting on physiological variations of renal perfusion, blood and/or plasma flow in healthy humans.

RESULTS

A total of 24 potential confounders were identified from the literature search and categorized into non-modifiable and modifiable factors. The non-modifiable factors include variables related to the demographics of a population (e.g. age, sex, and race) which cannot be manipulated but should be considered when interpreting RBF values between subjects. The modifiable factors include different activities (e.g. food/fluid intake, exercise training and medication use) that can be standardized in the study design. For each of the modifiable factors, evidence-based recommendations are provided to control for them in an RBF-measurement.

CONCLUSION

Future studies aiming to measure RBF are encouraged to follow a rigorous study design, that takes into account these recommendations for controlling the factors that can influence RBF results.

GABAergic and glutamatergic transmission reveals novel cardiovascular and urinary bladder control features in the shell nucleus accumbens

The shell Nucleus Accumbens (NAcc) projects to the lateral preoptic area, which is involved in the central micturition control and receives inputs from medullary areas involved in cardiovascular control. We investigated the role of GABAergic and glutamatergic transmission in the shell NAcc on intravesical pressure (IP) and cardiovascular control. Male Wistar rats with guide cannulas implanted bilaterally in the shell NAcc 7 days prior to the experiments were anesthetized with 2% isoflurane in 100% O2 and subjected to cannulation of the femoral artery and vein for mean arterial pressure (MAP) and heart rate recordings (HR) and infusion of drugs, respectively. The urinary bladder (UB) was cannulated for IP measurement. A Doppler flow probe was placed around the renal arterial for renal blood flow (RBF) measurement. After the baseline MAP, HR, IP and RBF recordings for 15 min, GABA or bicuculline methiodate (BMI) or L-glutamate or kynurenic acid (KYN) or saline (vehicle) were bilaterally injected into the shell NAcc and the variables were measured for 30 min. Data are as mean ± SEM and submitted to Student́s t test. GABA injections into the shell NAcc evoked a significant fall in MAP and HR and increased IP and RC compared to saline. L-glutamate in the shell NAcc increased MAP, HR and IP and reduced RC. Injections of BMI and KYN elicited no changes in the variables recorded. Therefore, the GABAergic and glutamatergic transmissions in neurons in the shell NAcc are involved in the neural pathways responsible for the central cardiovascular control and UB regulation.

Change in renal blood flow in response to intrarenal pressure alterations induced by ureteroscopy in an in-vivo porcine model

INTRODUCTION

High irrigation rates are commonly used during ureteroscopy and can increase intrarenal pressure (IRP) substantially. Concerns have been raised that elevated IRP may diminish renal blood flow (RBF) and perfusion of the kidney. Our objective was to investigate the real-time changes in RBF while increasing IRP during Ureteroscopy (URS) in an in-vivo porcine model.

METHODS

Four renal units in two porcine subjects were used in this study, three experimental units and one control. For the experimental units, RBF was measured by placing an ultrasonic flow cuff around the renal artery, while performing ureteroscopy in the same kidney using a prototype ureteroscope with a pressure sensor at its tip. Irrigation was cycled between two rates to achieve targeted IRPs of 30 mmHg and 100 mmHg. A control data set was obtained by placing the ultrasonic flow cuff on the contralateral renal artery while performing ipsilateral URS.

RESULTS

At high IRP, RBF was reduced in all three experimental trials by 10-20% but not in the control trial. The percentage change in RBF due to alteration in IRP was internally consistent in each porcine renal unit and independent of slower systemic variation in RBF encountered in both the experimental and control units.

CONCLUSION

RBF decreased 10-20% when IRP was increased from 30 to 100 mmHg during ureteroscopy in an in-vivo porcine model. While this reduction in RBF is unlikely to have an appreciable effect on tissue oxygenation, it may impact heat-sink capacity in vulnerable regions of the kidney.

The denervation or activation of renal sympathetic nerve and renal blood flow

The denervation or activation of the sympathetic nerve in the kidney can affect renal hemodynamics. The sympathetic nervous system regulates the physiological functions of the kidneys. Stimulation of sympathetic efferent nerves affects various parameters related to renal hemodynamics, including sodium excretion, renin secretion, and renal blood flow (RBF). Hence, renal sympathetic fibers may also play an essential role in regulating systemic vascular resistance and controlling blood pressure. In the absence of renal nerves, the hemodynamics response to stimuli is negligible or absent. The effect of renal sympathetic denervation on RBF is dependent on several factors such as interspecies differences, the basic level of nerve activity in the vessels or local density of adrenergic receptor in the vascular bed. The role of renal denervation has been investigated therapeutically in hypertension and related disorders. Hence, the dynamic impact of renal nerves on RBF enables using RBF dynamic criteria as a marker for renal denervation therapy.

Impaired renal autoregulation and pressure-natriuresis: any role in the development of heart failure in normotensive and angiotensin II-dependent hypertensive rats?

The aim of the present study was to assess the autoregulatory capacity of renal blood flow (RBF) and of the pressure-natriuresis characteristics in the early phase of heart failure (HF) in rats, normotensive and with angiotensin II (ANG II)-dependent hypertension. Ren-2 transgenic rats (TGR) were employed as a model of ANG II-dependent hypertension. HF was induced by creating the aorto-caval fistula (ACF). One week after ACF creation or sham-operation, the animals were prepared for studies evaluating in vivo RBF autoregulatory capacity and the pressure-natriuresis characteristics after stepwise changes in renal arterial pressure (RAP) induced by aortic clamping. In ACF TGR the basal mean arterial pressure, RBF, urine flow (UF), and absolute sodium excretion (UNaV) were all significantly lower tha n in sham-operated TGR. In the latter, reductions in renal arterial pressure (RAP) significantly decreased RBF whereas in ACF TGR they did not change. Stepwise reductions in RAP resulted in marked decreases in UF and UNaV in sham-operated as well as in ACF TGR, however, these decreases were significantly greater in the former. Our data show that compared with sham-operated TGR, ACF TGR displayed well-maintained RBF autoregulatory capacity and improved slope of the pressure-natriuresis relationship. Thus, even though in the very early HF stage renal dysfunction was demonstrable, in the HF model of ANG II-dependent hypertensive rat such dysfunction and the subsequent HF decompensation cannot be simply ascribed to impaired renal autoregulation and pressure-natriuresis relationship.

The role of Mas receptor on renal hemodynamic responses to angiotensin II administration in chronic renal sympathectomized male and female rats

Background and purpose

Renal hemodynamics is influenced by renal sympathetic nerves and the renin-angiotensin system. On the other hand, renal sympathetic denervation impacts kidney weight by affecting renal hemodynamics. The current study evaluated the role of the Mas receptor on renal hemodynamic responses under basal conditions and in response to angiotensin II (Ang II) in chronic renal sympathectomy in female and male rats.

Experimental approach

Forty-eight nephrectomized female and male rats were anesthetized and cannulated. Afterward, the effect of chronic renal sympathectomy was investigated on hemodynamic parameters such as renal vascular resistance (RVR), mean arterial pressure (MAP), and renal blood flow (RBF). In addition, the effect of chronic sympathectomy on kidney weight was examined.

Findings/Results

Chronic renal sympathectomy increased RVR and subsequently decreased RBF in both sexes. Renal perfusion pressure also increased after sympathectomy in male and female rats, while MAP did not change, significantly. In response to the Ang II injection, renal sympathectomy caused a greater decrease in RBF in all experimental groups, while it did not affect the MAP response. In addition, chronic sympathectomy increased left kidney weight in right nephrectomized rats.

Conclusion and implications

Chronic renal sympathectomy changed systemic/renal hemodynamics in baseline conditions and only renal hemodynamics in response to Ang II administration. Moreover, chronic sympathectomy increased compensatory hypertrophy in nephrectomized rats. These changes are unaffected by gender difference and Mas receptor blocker.

Renal blood flow during exercise: understanding its measurement with Doppler ultrasound

The sympathetic nervous system (SNS) has a critical role in continuously coordinating responses to stimuli internal and external to the human body by appropriately modulating the activity of the organs it innervates. The SNS is activated in response to various physiological stressors, including exercise, which can involve a significant increase in SNS activity. An increase in SNS activity directed towards the kidneys causes vasoconstriction of afferent arterioles within the kidneys. This sympathetically mediated renal vasoconstriction decreases renal blood flow (RBF), causing significant blood flow redistribution towards active skeletal muscles during exercise. In research studies, different modes, intensities, and durations of exercise have been used to investigate the sympathetically mediated RBF response to exercise, and several methodological approaches have been used to quantify RBF. Doppler ultrasound provides noninvasive, continuous, real-time measurements of RBF and has emerged as a valid and reliable technique to quantify RBF during exercise. This innovative methodology has been applied in studies in which the RBF response to exercise has been examined in healthy young and older adults and patient populations such as those with heart failure and peripheral arterial disease. This valuable tool has enabled researchers to produce clinically relevant findings that have furthered our understanding of the effect of SNS activation on RBF in populations of health and disease. Therefore, the focus of this narrative review is to highlight the use of Doppler ultrasound in research studies that has provided important findings furthering our knowledge of the impact of SNS activation on RBF regulation in humans.

A Novel Role of Semaphorin 3C in Modulating Systemic and Renal Hemodynamics

BACKGROUND

Alterations of renal hemodynamics play an essential role in renal homeostasis and kidney diseases. Recent data indicated that semaphorin 3C (SEMA3C), a secreted glycoprotein involved in vessel development, can modulate renal vascular permeability in acute kidney injury, but whether and how it might impact systemic and renal hemodynamics is unknown.

OBJECTIVES

The objective of the study was to explore the effect of SEMA3C on systemic and renal hemodynamics.

METHODS

SEMA3C recombinant protein was administered intravenously in two-month-old wild-type mice, and the variations of mean arterial pressure, heart rate, renal blood flow, and renal vascular resistance were measured and analyzed.

RESULTS

Acute administration of SEMA3C induced (i) systemic hemodynamic changes, including mean arterial pressure decrease and heart rate augmentation; (ii) renal hemodynamic changes, including reduced vascular resistance and elevated renal blood flow. Continuous perfusion of SEMA3C had no significant effect on systemic or renal hemodynamics.

CONCLUSION

SEMA3C is a potent vasodilator affecting both systemic and renal hemodynamics in mice.

Doppler ultrasound in the assessment of renal perfusion before and during continuous kidney replacement therapy in the pediatric intensive care unit

BACKGROUND

This study aimed to assess observer variability and describe renal resistive index (RRI) and pulsatility index (PI) before and after onset of continuous kidney replacement therapy (CKRT). A secondary objective was to correlate Doppler ultrasound findings with those from direct measurement of renal blood flow (RBF).

METHODS

This is a prospective observational study in hemodynamically stable Maryland piglets with and without acute kidney injury (AKI) and in hemodynamically unstable critically ill children requiring CKRT. Doppler-based RRI and PI were assessed for each subject. Measurements were made by two different operators (pediatric intensivists) before and after CKRT onset.

RESULTS

Observer variability assessment in the measurement of RRI and PI rendered a moderate correlation for both RRI (ICC 0.65, IQR 0.51-0.76) and PI (ICC 0.63, IQR 0.47-0.75). RRI and PI showed no correlation with RBF or urine output. Baseline RRI and PI were normal in control piglets [RRI 0.68 (SD 0.02), PI 1.25 (SD 0.09)] and those with AKI [RRI 0.68 (SD 0.03), PI 1.20 (SD 0.13)]. Baseline RRI and PI were elevated in critically ill children (RRI 0.85, PI 2.0). PI and RRI did not change with CKRT in any study group.

CONCLUSIONS

Observer variability between inexperienced pediatric intensivists was comparable with that between senior and junior operators. Doppler-based calculations did not correlate with invasive measurements of RBF. RRI and PI were normal in hemodynamically stable piglets with and without AKI. RRI and PI were high in hemodynamically unstable patients requiring CKRT. RRI and PI did not change after CKRT onset, despite changes in hemodynamic status. A higher resolution version of the Graphical abstract is available as Supplementary information.

Cerebral and renal hemodynamics: similarities, differences, and associations with chronic kidney disease and aortic hemodynamics

Elevated arterial pulsatility is a common risk factor for cerebrovascular disease and chronic kidney disease (CKD), which suggests that the brain and kidneys may have similar hemodynamic profiles. The objectives of this study were twofold: 1) to compare and contrast the cerebral and renal blood flow parameters in adults without CKD (hereafter, non-CKD adults) and CKD patients and 2) to determine the common predictor(s) of cerebral and renal hemodynamics among pressure pulsatility and several cardiovascular risk factors. In 110 non-CKD adults and 66 CKD patients, cerebral and renal blood flow velocity (BFV) were measured by transcranial Doppler and Duplex ultrasonography, respectively. Pulsatile hemodynamics were assessed by the pulsatility (PI) and resistive (RI) indices. Aortic pulse pressure was measured by tonometry. Compared with non-CKD adults, CKD patients showed greater pulsatility of the BFV (i.e., systolic minus diastolic BFV), PI, and RI in the kidneys but not the brain. However, the cerebral and renal PI and RI values were strongly correlated in both non-CKD adults (both PI and RI values: r_s = 0.695) and CKD patients (both PI and RI values: r_s = 0.640) (all P < 0.001). Multiple linear regression analysis further demonstrated that the cerebral and renal PI and RI associations remained significant after adjustment for potential covariates (e.g., age, sex, the presence of CKD). The aortic pulse pressure was a significant predictor for both cerebral and renal PI and RI values. Collectively, our findings suggest that CKD patients have higher renal flow pulsatility, which is strongly and independently associated with cerebral flow pulsatility and aortic hemodynamics.

Enhanced external counterpulsation: A new method to alleviate contrast-induced acute kidney injury

BACKGROUND

Contrast-induced acute kidney injury (CI-AKI) is a common complication after exposure to contrast media. Renal ischaemia occurs in the initial stage of CI-AKI, however, there are very few effective measures to improve renal perfusion.

METHODS

A total of 114 patients with an estimated glomerular filtration rate (eGFR) of 60-89 ml/min/1.73m² were randomly assigned to two groups: enhanced external counterpulsation (EECP) group (N = 57) and control group (N = 57). Two hours after contrast exposure, EECP group received EECP treatment for 1 h while no intervention was performed control group. The primary outcome was the incidence of serum cystatin C concentration to 10% above the baseline concentration at 24 h after contrast administration. The secondary outcomes were the incidence of CI-AKI (defined as an increase in serum creatinine concentration to ≥0.5 mg/dl or by 25% compare to the baseline after contrast exposure), contrast clearance and adverse clinical events.

RESULTS

The primary outcome was observed in 26 patients (6 EECP and 20 control; 11% vs. 35%; P = 0.002). CI-AKI occurred in four patients (0 EECP and 4 control; 0% vs. 7%; P = 0.042). The clearance rate of iopromide in the initial 3 h was significantly different between EECP and control group (59.92 ± 8.84 vs 46.80 ± 9.26 ml/min/1.73 m²; P < 0.001). No adverse clinical events were observed in this study.

CONCLUSIONS

This study demonstrates that EECP increases the contrast clearance and may have an effect in reducing the risk of CI-AKI. The study has been registered in Chinese Clinical Trial Registry (ChiCTR 2,000,039,190).

Eukaryotic elongation factor 2 kinase inhibitor, A484954 induces diuretic effect via renal vasorelaxation in spontaneously hypertensive rats

Eukaryotic elongation factor 2 (eEF2) kinase (eEF2K), alternatively known as calmodulin-dependent protein kinase III, inhibits protein translation via phosphorylating its sole substrate, eEF2. We previously demonstrated that expression and activity of eEF2K change in mesenteric artery from spontaneously hypertensive rats (SHR) with aging and that eEF2K is involved in pathogenesis of essential hypertension. In addition, we have recently revealed that acute intravenous injection with A484954, a selective eEF2K inhibitor, lowers blood pressure specifically in SHR partly via inducing vasorelaxation. In this study, we examined whether A484954 induces diuretic effect. After male SHR and normotensive Wistar Kyoto rats (WKY) were given a single intraperitoneal injection of A484954 (2.5 mg/kg, 0.5-9 h), urine was collected using metabolic cage. Contraction of isolated renal arteries form SHR was isometrically measured. While A484954 did not induce diuretic effect in WKY, it increased urine output, water intake, and urinary sodium excretion in SHR. A484954 (10 μM) induced vasorelaxation in isolated renal arteries, which was inhibited by a β-adrenergic receptor antagonist, propranolol. It was confirmed that A484954 increased renal blood flow in SHR as measured by renal ultrasonography. In summary, it was for the first time revealed that A484954 induces diuretic effect in SHR at least partly via renal vasorelaxation through β-adrenergic receptor.

Effects of systemic and renal intramedullary endothelin-1 receptor blockade on tissue NO and intrarenal hemodynamics in normotensive and hypertensive rats

Endothelin 1 (ET-1) seems essential in salt-dependent hypertension, and activation of ETA receptors causes renal vasoconstriction. However, the response in the renal medulla and the role of tissue NO availability has never been adequately explored in vivo. We examined effects of ETA and ETB receptor blockade (atrasentan and BQ788) on blood pressure (MAP), medullary blood flow (MBF) and medullary tissue NO. Effects of systemic and intramedullary blocker application were compared in anesthetized normotensive ET-1-pretreated Sprague-Dawley rats (S-D), in salt-dependent hypertension (HS/UNX) and in spontaneously hypertensive rats (SHR). Total renal blood flow (RBF) was measured using a Transonic renal artery probe, MBF as laser-Doppler flux, and tissue NO signal using selective electrodes. In normotensive rats ET-1 significantly increased MAP, decreased RBF (-20%) and renal medullary NO. In HS/UNX rats atrasentan decreased MAP and increased medullary NO, earlier and more profoundly with intravenous infusion. In SHR atrasentan decreased MAP, more effectively with intravenous infusion; the increase in tissue NO (∼10%) was similar with both routes; however, only intramedullary atrasentan increased MBF. No consistent responses to BQ788 were seen. We confirmed dominant role of ETA receptors in regulation of blood pressure and renal hemodynamics in normotensive and hypertensive rats and provided novel evidence for the role of ETA in control of intrarenal NO bioavailability in salt-dependent and spontaneous hypertension. Under conditions of activation of the endothelin system ETB stimulation preserved medullary perfusion.

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.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40658-021-00389-0.

Detection of Changes in Renal Blood Flow Using Arterial Spin Labeling MRI

BACKGROUND

Alteration in kidney perfusion is an early marker of renal damage. The purpose of this study was to evaluate if changes in renal blood flow (RBF) could be detected using MRI with arterial spin labeling (ASL) technique.

METHODS

RBF as assessed by cortical (CRBF), medullary, and total renal blood flow (TRBF) were measured by MRI with arterial spin labeling (ASL-MRI) using flow-sensitive alternating inversion recovery true fast imaging with steady-state precession sequence. In 11 normotensive healthy individuals (NT) and 11 hypertensive patients (HT), RBF was measured at baseline and after both feet were covered with cold ice packs (cold pressor test) that activates the sympathetic nervous system. In another experiment, RBF was measured in 10 patients with CKD before and after a pharmacological intervention. We compared RBF measurements between the 3 study populations.

RESULTS

A significant reduction in CRBF (p = 0.042) and a trend in TRBF (p = 0.053) were observed in response to the activation of the sympathetic nervous system. A trend toward reduction of CRBF (p = 0.051) and TRBF (p = 0.059) has been detected after pharmacological intervention. TRBF was significantly lower in patients with HT and CKD patients compared to NT individuals (NT vs. HT, p = 0.014; NT vs. CKD, p = 0.004). TRBF was lower in patients with CKD compared to HT (p = 0.047).

CONCLUSION

Our data indicate that both acute and short-term changes in RBF could be detected using ASL-MRI. We were able to detect differences in RBF between healthy and diseased individuals by needing only small sample size per group. Thus, ASL-MRI offers an advantage in conducting clinical trials compared to other technologies.

Renal vascular TRP channels

Members of the transient receptor potential (TRP) channels that are expressed in the kidney have gained prominence in recent years following discoveries of their role in maintaining the integrity of the filtration barrier, regulating tubular reabsorption of Ca²⁺ and Mg²⁺, and sensing osmotic stimuli. Furthermore, evidence has linked mutations in TRP channels to kidney disease pathophysiological mechanisms, including focal segmental glomerulosclerosis, disturbances in Mg²⁺ homeostasis, and polycystic kidney disease. Several subtypes of TRP channels are expressed in the renal vasculature, from preglomerular arteries and arterioles to the descending vasa recta. Although investigations on the physiological and pathological significance of renal vascular TRP channels are sparse, studies on isolated vessels and cells have suggested their involvement in renal vasoregulation. Renal blood flow (RBF) is an essential determinant of kidney function, including glomerular filtration, water and solute reabsorption, and waste product excretion. Functional alterations in ion channels that are expressed in the endothelium and smooth muscle of renal vessels can modulate renal vascular resistance, arterial pressure, and RBF. Hence, renal vascular TRP channels are potential therapeutic targets for the treatment of kidney disease. This review summarizes the current knowledge of TRP channel expression in renal vasculature and their role in controlling kidney function in health and disease.

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TRP channels are widely distributed in mammalian kidneys in glomerular, tubular, and vascular cells.

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TRPC and TRPV channels are functionally expressed in afferent arterioles.

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TRPC4 may regulate Ca²⁺ signaling in the descending vasa recta.

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Smooth muscle, endothelial, and pericyte TRP channels may participate in signal transduction mechanisms.

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TRP channels underlie renal autoregulation and regional kidney perfusion in health and disease.

Renal Sympathetic Denervation Attenuates Congestive Heart Failure in Angiotensin II-Dependent Hypertension: Studies with Ren-2 Transgenic Hypertensive Rats with Aortocaval Fistula

OBJECTIVE

We examined if renal denervation (RDN) attenuates the progression of aortocaval fistula (ACF)-induced heart failure or improves renal hemodynamics in Ren-2 transgenic rats (TGR), a model of angiotensin II (ANG II)-dependent hypertension.

METHODS

Bilateral RDN was performed 1 week after creation of ACF. The animals studied were ACF TGR and sham-operated controls, and both groups were subjected to RDN or sham denervation. In separate groups, renal artery blood flow (RBF) responses were determined to intrarenal ANG II (2 and 8 ng), norepinephrine (NE) (20 and 40 ng) and acetylcholine (Ach) (10 and 40 ng) 3 weeks after ACF creation.

RESULTS

In nondenervated ACF TGR, the final survival rate was 10 versus 50% in RDN rats. RBF was significantly lower in ACF TGR than in sham-operated TGR (6.2 ± 0.3 vs. 9.7 ± 0.5 mL min-1 g-1, p < 0.05), the levels unaffected by RDN. Both doses of ANG II decreased RBF more in ACF TGR than in sham-operated TGR (-19 ± 3 vs. -9 ± 2% and -47 ± 3 vs. -22 ± 2%, p < 0.05 in both cases). RDN did not alter RBF responses to the lower dose, but increased it to the higher dose of ANG II in sham-operated as well as in ACF TGR. NE comparably decreased RBF in ACF TGR and sham-operated TGR, and RDN increased RBF responsiveness. Intrarenal Ach increased RBF significantly more in ACF TGR than in sham-operated TGR (29 ± 3 vs. 17 ± 3%, p < 0.05), the changes unaffected by RDN. ACF creation induced marked bilateral cardiac hypertrophy and lung congestion, both attenuated by RDN. In sham-operated but not in ACF TGR, RDN significantly decreased mean arterial pressure.

CONCLUSION

The results show that RDN significantly improved survival rate in ACF TGR; however, this beneficial effect was not associated with improvement of reduced RBF or with attenuation of exaggerated renal vascular responsiveness to ANG II.

Interplay of the adenosine system and NO in control of renal haemodynamics and excretion: Comparison of normoglycaemic and streptozotocin diabetic rats

The adenosine (Ado) system may participate in regulation of kidney function in diabetes mellitus (DM), therefore we explored its role and interrelation with NO in the control of renal circulation and excretion in normoglycemic (NG) and streptozotocin-diabetic (DM) rats. Effects of theophylline (Theo), a non-selective Ado receptor antagonist, were examined in anaesthetized NG or in streptozotocin induced diabetic (DM) rats, untreated or after blockade of NO synthesis with l-NAME. We measured arterial blood pressure (MABP), whole kidney blood flow and renal regional flows: cortical and outer- and inner-medullary (IMBF), determined as laser-Doppler fluxes. Renal excretion of water, total solutes and sodium and in situ renal tissue NO signal (selective electrodes) were also determined. Theo experiments disclosed minor baseline vasoconstrictor and vasodilator tone in the kidney of NG and DM rats, respectively. NO blockade increased baseline MABP and decreased renal haemodynamics, similarly in NG and DM rats, indicating comparable vasodilator influence of NO in the two groups. Unexpectedly, in all rats with intact NO synthesis, Ado receptor blockade increased kidney tissue NO. In NO-deficient NG and DM rats, Ado receptor blockade induced comparable renal vasodilatation, suggesting similar vasoconstrictor influence of the Ado system. However, DM rats showed an unexplained association of decreased MABP and IMBF and increased NO signal. Higher baseline renal excretion in DM rats indicated inhibition of renal tubular reabsorption due to the prevalence of natriuretic A2 over antinatriuretic A1 receptors. In conclusion, the experiments provided new insights in functional interrelation of adenosine and NO in normoglycaemia and streptozotocin-diabetes.

4D flow MRI for the assessment of renal transplant dysfunction: initial results

OBJECTIVES

(1) Determine inter-observer reproducibility and test-retest repeatability of 4D flow parameters in renal allograft vessels; (2) determine if 4D flow measurements in the renal artery (RA) and renal vein (RV) can distinguish between functional and dysfunctional allografts; (3) correlate haemodynamic parameters with estimated glomerular filtration rate (eGFR), perfusion measured with dynamic contrast-enhanced MRI (DCE-MRI) and histopathology.

METHODS

Twenty-five prospectively recruited renal transplant patients (stable function/chronic renal allograft dysfunction, 12/13) underwent 4D flow MRI at 1.5 T. 4D flow coronal oblique acquisitions were performed in the transplant renal artery (RA) (velocity encoding parameter, VENC = 120 cm/s) and renal vein (RV) (VENC = 45 cm/s). Test-retest repeatability (n = 3) and inter-observer reproducibility (n = 10) were assessed by Cohen's kappa, coefficient of variation (CoV) and Bland-Altman statistics. Haemodynamic parameters were compared between patients and correlated to the estimated glomerular filtration rate, DCE-MRI parameters (n = 10) and histopathology from allograft biopsies (n = 15).

RESULTS

For inter-observer reproducibility, kappa was > 0.99 and 0.62 and CoV of flow was 12.6% and 7.8% for RA and RV, respectively. For test-retest repeatability, kappa was > 0.99 and 0.5 and CoV of flow was 27.3% and 59.4%, for RA and RV, respectively. RA (p = 0.039) and RV (p = 0.019) flow were both significantly reduced in dysfunctional allografts. Both identified chronic allograft dysfunction with good diagnostic performance (RA: AUC = 0.76, p = 0.036; RV: AUC = 0.8, p = 0.018). RA flow correlated negatively with histopathologic interstitial fibrosis score ci (ρ = - 0.6, p = 0.03).

CONCLUSIONS

4D flow parameters had better repeatability in the RA than in the RV. RA and RV flow can identify chronic renal allograft dysfunction, with RA flow correlating with histopathologic interstitial fibrosis score.

KEY POINTS

• Inter-observer reproducibility of 4D flow measurements was acceptable in both the transplant renal artery and vein, but test-retest repeatability was better in the renal artery than in the renal vein. • Blood flow measurements obtained with 4D flow MRI in the renal artery and renal vein are significantly reduced in dysfunctional renal transplants. • Renal transplant artery flow correlated negatively with histopathologic interstitial fibrosis score.

A randomized, controlled, double-blind crossover study on the effects of isoeffective and isovolumetric intravenous crystalloid and gelatin on blood volume, and renal and cardiac hemodynamics

BACKGROUND & AIMS

Blood volume expanding properties of colloids are superior to crystalloids. In addition to oncotic/osmotic properties, the electrolyte composition of infusions may have important effects on visceral perfusion, with infusions containing supraphysiological chloride causing hyperchloremic acidosis and decreased renal blood flow. In this non-inferiority study, a validated healthy human subject model was used to compare effects of colloid (4% succinylated gelatin) and crystalloid fluid regimens on blood volume, renal function, and cardiac output.

METHODS

Healthy male participants were given infusions over 60 min > 7 days apart in a randomized, crossover manner. Reference arm (A): 1.5 L of Sterofundin ISO, isoeffective arm (B): 0.5 L of 4% Gelaspan®, isovolumetric arm (C): 0.5 L of 4% Gelaspan® and 1 L of Sterofundin ISO (all B. Braun, Melsungen, Germany). Participants were studied over 240 min. Changes in blood volume were calculated from changes in weight and hematocrit. Renal volume, renal artery blood flow (RABF), renal cortex perfusion and diffusion, and cardiac index were measured with magnetic resonance imaging.

RESULTS

Ten of 12 males [mean (SE) age 23.9 (0.8) years] recruited, completed the study. Increase in body weight and extracellular fluid volume were significantly less after infusion B than infusions A and C, but changes in blood volume did not significantly differ between infusions. All infusions increased renal volume, with no significant differences between infusions. There was no significant difference in RABF across the infusion time course or between infusion types. Renal cortex perfusion decreased during the infusion (mean 18% decrease from baseline), with no significant difference between infusions. There was a trend for increased renal cortex diffusion (4.2% increase from baseline) for the crystalloid infusion. All infusions led to significant increases in cardiac index.

CONCLUSIONS

A smaller volume of colloid (4% succinylated gelatin) was as effective as a larger volume of crystalloid at expanding blood volume, increasing cardiac output and changing renal function. Significantly less interstitial space expansion occurred with the colloid.

TRIAL REGISTRATION

The protocol was registered with the European Union Drug Regulating Authorities Clinical Trials Database (https://eudract.ema.europa.eu) (EudraCT No. 2013-003260-32).

Differential effects of inotropes and inodilators on renal function in acute cardiac care

Pathological interplay between the heart and kidneys is widely encountered in heart failure (HF) and is linked to worse prognosis and quality of life. Inotropes, along with diuretics and vasodilators, are a core medical response to HF but decompensated patients who need inotropic support often present with an acute worsening of renal function. The impact of inotropes on renal function is thus potentially an important influence on the choice of therapy. There is currently relatively little objective data available to guide the selection of inotrope therapy but recent direct observations on the effects of levosimendan and milrinone on glomerular filtration favour levosimendan. Other lines of evidence indicate that in acute decompensated HF levosimendan has an immediate renoprotective effect by increasing renal blood flow through preferential vasodilation of the renal afferent arterioles and increases in glomerular filtration rate: potential for renal medullary ischaemia is avoided by an offsetting increase in renal oxygen delivery. These indications of a putative reno-protective action of levosimendan support the view that this calcium-sensitizing inodilator may be preferable to dobutamine or other adrenergic inotropes in some settings by virtue of its renal effects. Additional large studies will be required, however, to clarify the renal effects of levosimendan in this and other relevant clinical situations, such as cardiac surgery.

Comparison of multi-delay FAIR and pCASL labeling approaches for renal perfusion quantification at 3T MRI

OBJECTIVE

To compare the most commonly used labeling approaches, flow-sensitive alternating inversion recovery (FAIR) and pseudocontinuous arterial spin labeling (pCASL), for renal perfusion measurement using arterial spin labeling (ASL) MRI.

METHODS

Multi-delay FAIR and pCASL were performed in 16 middle-aged healthy volunteers on two different occasions at 3T. Relative perfusion-weighted signal (PWS), temporal SNR (tSNR), renal blood flow (RBF), and arterial transit time (ATT) were calculated for the cortex and medulla in both kidneys. Bland-Altman plots, intra-class correlation coefficient, and within-subject coefficient of variation were used to assess reliability and agreement between measurements.

RESULTS

For the first visit, RBF was 362 ± 57 and 140 ± 47 mL/min/100 g, and ATT was 0.47 ± 0.13 and 0.70 ± 0.10 s in cortex and medulla, respectively, using FAIR; RBF was 201 ± 72 and 84 ± 27 mL/min/100 g, and ATT was 0.71 ± 0.25 and 0.86 ± 0.12 s in cortex and medulla, respectively, using pCASL. For both labeling approaches, RBF and ATT values were not significantly different between visits. Overall, FAIR showed higher PWS and tSNR. Moreover, repeatability of perfusion parameters was better using FAIR.

DISCUSSION

This study showed that compared to (balanced) pCASL, FAIR perfusion values were significantly higher and more comparable between visits.

Effects of milrinone on renal perfusion, filtration and oxygenation in patients with acute heart failure and low cardiac output early after cardiac surgery

PURPOSE

Early postoperative heart failure is common after cardiac surgery, and inotrope treatment may impact renal perfusion and oxygenation. We aimed to study the renal effects of the inodilator milrinone when used for the treatment of heart failure after weaning from cardiopulmonary bypass (CPB).

MATERIAL AND METHODS

In 26 patients undergoing cardiac surgery with CPB, we used renal vein catheterization to prospectively measure renal blood flow (RBF), glomerular filtration rate (GFR), and renal oxygenation. Patients who developed acute heart failure and low cardiac output (cardiac index <2.1 L/min/m²) at 30 min after weaning from CPB (n = 7) were given milrinone, and the remaining patients (n = 19) served as controls. Additional measurements were made at 60 min after CPB.

RESULTS

In patients with acute postoperative heart failure, before receiving milrinone, renal blood flow was lower (-33%, p < .05) while renal oxygen extraction was higher (41%, p < .05) compared to the control group. Milrinone increased cardiac index (21%, p < .001), RBF (36%, p < .01) and renal oxygen delivery (35%, p < .01), with no significant change in GFR and oxygen consumption compared to the control group.

CONCLUSIONS

In patients with acute heart failure after weaning from CPB, the milrinone-induced increase in cardiac output was accompanied by improved renal oxygenation.

TRIAL REGISTRATION

ClinicalTrials.gov; identifier NCT02405195, date of registration; March 27, 2015, and NCT02549066, date of registration; 9 September 2015.

Fluid Overload and Acute Kidney Injury

Commonest intervention in hospitalized patient is fluid therapy, and practically every critically ill patient receives fluid resuscitation. Commonest indication for fluid administration is to achieve hemodynamic stability and prevent or manage acute kidney injury (AKI). However, fluid administration is a two-edged sword, i.e., inadequate fluids give rise to hypoperfusion and organ injury and overzealous fluid therapy can give rise to fluid overload and related consequences. Though fluids are commonly given to prevent development of AKI, hypervolemia itself has the potential to cause AKI.

Consensus-based technical recommendations for clinical translation of renal ASL MRI

OBJECTIVES

This study aimed at developing technical recommendations for the acquisition, processing and analysis of renal ASL data in the human kidney at 1.5 T and 3 T field strengths that can promote standardization of renal perfusion measurements and facilitate the comparability of results across scanners and in multi-centre clinical studies.

METHODS

An international panel of 23 renal ASL experts followed a modified Delphi process, including on-line surveys and two in-person meetings, to formulate a series of consensus statements regarding patient preparation, hardware, acquisition protocol, analysis steps and data reporting.

RESULTS

Fifty-nine statements achieved consensus, while agreement could not be reached on two statements related to patient preparation. As a default protocol, the panel recommends pseudo-continuous (PCASL) or flow-sensitive alternating inversion recovery (FAIR) labelling with a single-slice spin-echo EPI readout with background suppression and a simple but robust quantification model.

DISCUSSION

This approach is considered robust and reproducible and can provide renal perfusion images of adequate quality and SNR for most applications. If extended kidney coverage is desirable, a 2D multislice readout is recommended. These recommendations are based on current available evidence and expert opinion. Nonetheless they are expected to be updated as more data become available, since the renal ASL literature is rapidly expanding.

Consensus-based technical recommendations for clinical translation of renal ASL MRI

Objectives

This study aimed at developing technical recommendations for the acquisition, processing and analysis of renal ASL data in the human kidney at 1.5 T and 3 T field strengths that can promote standardization of renal perfusion measurements and facilitate the comparability of results across scanners and in multi-centre clinical studies.

Methods

An international panel of 23 renal ASL experts followed a modified Delphi process, including on-line surveys and two in-person meetings, to formulate a series of consensus statements regarding patient preparation, hardware, acquisition protocol, analysis steps and data reporting.

Results

Fifty-nine statements achieved consensus, while agreement could not be reached on two statements related to patient preparation. As a default protocol, the panel recommends pseudo-continuous (PCASL) or flow-sensitive alternating inversion recovery (FAIR) labelling with a single-slice spin-echo EPI readout with background suppression and a simple but robust quantification model.

Discussion

This approach is considered robust and reproducible and can provide renal perfusion images of adequate quality and SNR for most applications. If extended kidney coverage is desirable, a 2D multislice readout is recommended. These recommendations are based on current available evidence and expert opinion. Nonetheless they are expected to be updated as more data become available, since the renal ASL literature is rapidly expanding.

Electronic supplementary material

The online version of this article (10.1007/s10334-019-00800-z) contains supplementary material, which is available to authorized users.

Phase-contrast magnetic resonance imaging to assess renal perfusion: a systematic review and statement paper

Objective

Phase-contrast magnetic resonance imaging (PC-MRI) is a non-invasive method used to compute blood flow velocity and volume. This systematic review aims to discuss the current status of renal PC-MRI and provide practical recommendations which could inform future clinical studies and its adoption in clinical practice.

Methodology

A comprehensive search of all the PC-MRI studies in human healthy subjects or patients related to the kidneys was performed.

Results

A total of 39 studies were included in which PC-MRI was used to measure renal blood flow (RBF) alongside other derivative hemodynamic parameters. PC-MRI generally showed good correlation with gold standard methods of RBF measurement, both in vitro and in vivo, and good reproducibility. Despite PC-MRI not being routinely used in clinical practice, there are several clinical studies showing its potential to support diagnosis and monitoring of renal diseases, in particular renovascular disease, chronic kidney disease and autosomal dominant polycystic kidney disease.

Discussion

Renal PC-MRI shows promise as a non-invasive technique to reliably measure RBF, both in healthy volunteers and in patients with renal disease. Future multicentric studies are needed to provide definitive normative ranges and to demonstrate the clinical potential of PC-MRI, likely as part of a multi-parametric renal MRI protocol.

Electronic supplementary material

The online version of this article (10.1007/s10334-019-00772-0) contains supplementary material, which is available to authorized users.

TRPV1 protects renal ischemia-reperfusion injury in diet-induced obese mice by enhancing CGRP release and increasing renal blood flow

Background

Obesity is a major risk factor for end-stage renal disease. Using transient receptor potential vanilloid 1 knockout (TRPV1^−/−) mice, we tested the hypothesis that TRPV1 protects against obesity-induced exacerbation of renal ischemia-reperfusion (I/R) injury.

Methods

TRPV1^−/− and wild-type (WT) mice were fed a chow or Western diet (WD) for 22–23 weeks. After that, mice were subjected to renal I/R injury, and renal cortical blood flow (CBF) and medullary blood flow (MBF) were measured.

Results

The Western diet significantly increased body weight and fasting blood glucose levels in both TRPV1^−/− and WT mice. WD-induced impairment of glucose tolerance was worsened in TRPV1^−/− mice compared with WT mice. WD intake prolonged the time required to reach peak reperfusion in the cortex and medulla (both P < 0.05), decreased the recovery rate of CBF (P < 0.05) and MBF (P < 0.05), and increased blood urea nitrogen, plasma creatinine, and urinary 8-isoprostane levels after I/R in both mouse strains, with greater effects in TRPV1^−/− mice (all P < 0.05). Renal I/R increased calcitonin gene-related peptide (CGRP) release in WT but not in TRPV1^−/− mice, and WD attenuated CGRP release in WT mice. Moreover, blockade of CGRP receptors impaired renal regional blood flow and renal function in renal I/R injured WT mice.

Conclusion

These results indicate that TRPV1 plays a protective role in WD-induced exacerbation of renal I/R injury probably through enhancing CGRP release and increasing renal blood flow.

Magnesium lithospermate B improves renal hemodynamics and reduces renal oxygen consumption in 5/6th renal ablation/infarction rats

BACKGROUND

Magnesium lithospermate B (MLB) can promote renal microcirculation. The aim of the current project was to study whether MLB improves renal hemodynamics, oxygen consumption and subsequently attenuates hypoxia in rats induced by 5/6th renal Ablation/Infarction(A/I).

METHODS

Chronic renal failure (CRF) was induced in male SD rats by the 5/6 (A/I) surgery. 30 rats were randomly divided into three groups: sham group, 5/6 (A/I) + vehicle group (CRF group) and 5/6 (A/I) + MLB (CRF + MLB) group. 28 days after the surgery, rats were given with saline or 100 mg/kg MLB by i.p. injection for 8 weeks. The 24-h urinary protein (24hUp), serum creatinine (Scr), blood urine nitrogen (BUN), systolic blood pressure (SBP) and diastolic blood pressure (DBP) were measured. The protein expression of Fibronectin (FN), Collagen-I (Col-I), Connective Tissue Growth Factor(CTGF) and Interleukin-6 (IL-6) were measured by Western blot. Renal blood flow (RBF) and renal O₂ consumption (QO₂) indicated as sodium reabsorption (QO₂/TNa) were detected before sacrifice. Renal hypoxia was assessed by measuring the protein expression of nNOS, HIF-1α and VEGF.

RESULTS

MLB significantly reduced 24hUp, Scr, BUN, SBP and DBP levels in rats with CRF. The expression of FN, Col-I, CTGF and IL-6 were down-regulated by MLB treatment in rats with CRF. In comparison to sham operated rats, 5/6 (A/I) rats had significantly lower RBF, and MLB significantly increased RBF in rats with CRF. Moreover, QO₂/TNa was higher in the CRF group as compared to that in the sham group, and it was significantly attenuated in the CRF + MLB group. MLB reversed the expression of nNOS (neuronal nitric oxide synthase), HIF-1α (hypoxia inducible factor-1) and VEGF in rats with CRF.

CONCLUSIONS

MLB improves renal function, fibrosis and inflammation in CRF rats induced by 5/6 (A/I), which is probably related to the increase in RBF, reduction of oxygen consumption and attenuation of renal hypoxia in the remnant kidney with CRF.

Effect of exercise intensity on renal blood flow in patients with chronic kidney disease stage 2

BACKGROUND

Acute exercise reduces renal blood flow (RBF). However, the effect of exercise intensity on RBF in patients with chronic kidney disease (CKD) stage 2 is not known. We investigated the association between RBF and exercise intensity in patients with CKD stage 2 using pulsed Doppler ultrasonography.

METHODS

Eight men with CKD stage 2 (cystatin C-based estimate of glomerular filtration rate: 60-89 ml/min/1.73 m²) participated in this study. Using a bicycle ergometer, participants undertook a maximal graded exercise test (MGET) (experiment 1) and a multi-stage exercise test (experiment 2) to determine their lactate threshold (LT). Participants undertook a multi-stage exercise test for 4-min each. Workloads of 60%, 80%, 100%, 120%, and 140% of LT were used in experiment 3. RBF was measured by pulsed Doppler ultrasonography at rest, immediately after exercise, and 1 h after exercise in experiment 1, and at rest and immediately after each exercise bout in experiment 3.

RESULTS

Renal blood flow after the MGET was 52% lower than at rest, and did not recover as well as after the exercise test. Cross-sectional area (CSA) was significantly lower after graded exercise. RBF tended to be lower at 100% of LT and was significantly lower at 120% of LT. CSA was significantly lower at 100% of LT.

CONCLUSIONS

Renal blood flow does not change during exercise until the LT is reached. These findings may assist in making appropriate exercise recommendations to patients with CKD stage 2.

Mas receptor antagonist (A799) alters the renal hemodynamics responses to angiotensin II administration after renal moderate ischemia/reperfusion in rats: gender related differences

Moderate renal ischemia/reperfusion (I/R) injury is one of the major causes of kidney failure. We examined the role of Mas receptor (MasR) antagonist (A779) alone and combined with angiotensin II (Ang II) type 2 receptor (AT2R) antagonist (PD123319) on renal hemodynamic responses to Ang II after moderate I/R in male and female rats. Anaesthetized Wistar rats underwent 30 min partial ischemia by reduction of renal perfusion pressure (RPP) and subjected to block vasodepressor receptors followed by Ang II (100 and 300 ng/kg/min) infusion. Mean arterial pressure (MAP), renal blood flow (RBF), and renal vascular resistance (RVR) responses were assessed during graded Ang II infusion at controlled RPP. Thirty min post reperfusion, the Ang II infusion reduced RBF and increased RVR in a dose-related fashion (P < 0.05). However, A779 alone or A779 plus PD123319 infusion increased the RBF and RVR responses to Ang II infusion significantly (P < 0.05) in female but not in the male rats. MasR antagonist altered the RBF and RVR responses to Ang II infusion in female, and these responses were not altered statistically in dual blockade of MasR and AT2R. These findings suggest the important role of Mas receptor in renal vascular response to Ang II in female rats after moderate I/R.

A rat model of acute kidney injury through systemic hypoperfusion evaluated by micro-US, color and PW-Doppler

AIM

To create an animal model of acute renal ischemia induced by systemic hypoperfusion, controllable and reproducible to study, in real time, hemorrhagic shock changes with micro-imaging.

ANIMALS AND METHODS

Hemorrhagic shock was induced in rats activating a syringe pump setup to remove 1 mL/min of blood, through the femoral artery catheter. The withdrawal was continued until the mean arterial pressure (MAP) dropped to 25-30 mmHg. For the next 60 min, the MAP was maintained at a constant pressure value, by automatic pump infusion and withdrawal. Micro-ultrasound imaging was performed using the Vevo 2100 system with the MS250 transducer (13-24 MHz). Renal size, morphology and echogenicity were evaluated in B-mode. Renal blood flow was evaluated using color and PW-Doppler.

RESULTS

After 1 h of ischemia, B-mode images documented slight changes in kidney echogenicity. Color and PW-Doppler analysis showed a reduction in renal blood flow in kidneys during the hypoperfusion with a progressive and significant change from baseline values of resistive index (RI). At the histological evaluation, 60 min of hypoperfusion resulted in ischemic changes in the kidneys.

CONCLUSIONS

The results of this experimental study encourage the use of the described model to study acute renal ischemia trough severe hypoperfusion. The histological data confirmed that the model was able to produce injury in renal parenchyma. It can be used to assess acute ischemic damage not only in the kidney but also in other organs by using all available dedicated small animals imaging techniques.

Endothelial prostacyclin protects the kidney from ischemia-reperfusion injury

Prostacyclin, or PGI₂, is a product of PGI synthase (PGIS), down-stream of cyclooxygenase pathway. PGI₂ has been demonstrated to play an important role in maintaining renal blood flow. Non-steroidal anti-inflammatory drugs (NSAIDs) that inhibit cyclooxygenase are reported to increase the susceptibility of patients to acute kidney injury (AKI). This study explores the role of endothelium-derived prostacyclin in ischemia-reperfusion injury (I/RI). The renal PGIS expression and PGI₂ production markedly increased following I/RI. Loss of one allele of PGIS gene or selective endothelial PGIS deletion (TEK-CRE PGIS^fl/fl mice) caused more severe renal damage following I/RI than control mice. Iloprost, a PGI₂ analog, administered 30 min before the I/R surgery, markedly attenuated the renal damage in both control mice and TEK-CRE PGIS^fl/fl mice. Renal p-PKA expression significantly increased after I/RI in wild-type mice but not in the PGIS deletion mice, consistent with IP receptor mediating the protective effect. Further studies showed that PGIS deficiency was associated with reduced fluorescence microsphere accumulation in the kidney following I/R. Folic acid also induced marked kidney injury; however, endothelial PGIS deletion did not worsen kidney injury compared with wild-type mice. These studies indicate that PGIS-derived PGI₂ can protect the kidney from acute injury caused by ischemia and reperfusion and PGIS/PGI₂ is a potential intervention target for AKI.

Meal Ingestion and Hemodynamic Interactions Regarding Renal Blood Flow on Duplex Sonography: Potential Diagnostic Implications

Splanchnic blood flow changes dramatically after meal ingestion. The present study evaluated physiologic interactions between meal ingestion and hemodynamics with respect to renal blood flow on duplex sonography, assessing the possible influence on Doppler parameters used as diagnostic criteria for renal artery stenosis. Subjects comprised 26 healthy young men (mean age: 22 ± 2 y). Sonographic measurements were made shortly after breakfast and every 1 h thereafter and were compared with values measured before the meal. Peak systolic velocity in the renal artery was elevated post-prandially, peaking at 1 h (90 ± 12 cm/s), compared with pre-prandially (73 ± 10 cm/s, p < 0.01). Similarly, acceleration time at the intra-renal segmental artery shortened to a minimum at 1 h (45 ± 5 ms) compared with baseline (51 ± 6 ms, p < 0.01). The present study indicates that renal blood flow is altered for a few hours after meal ingestion. Attention should be paid to the interpretation of data measured after meals on duplex sonography for diagnosis of renal artery stenosis.

Effects of acute ethanol intoxication in an ovine peritonitis model

BACKGROUND

Acute ethanol intoxication has been shown to have contrasting effects on outcomes in sepsis. The aim of this study was to explore the effects of acute ethanol intoxication on hemodynamics, renal function, brain perfusion and lactate/pyruvate in an ovine sepsis model.

METHODS

Anesthetized, mechanically ventilated female sheep were randomized to an ethanol group (n = 7), which received 1 g/kg ethanol diluted in intravenous (i.v.) saline infusion or a control group (n = 7), which received the same volume of i.v. saline. Both groups received the treatment for a period of 2 h prior to induction of sepsis by intraperitoneal injection of feces. Other treatment included fluid resuscitation but no vasopressors or antibiotics. Global hemodynamics, renal blood flow, brain cortex laser Doppler flowmetry and microdialysis analyses were recorded hourly.

RESULTS

In the ethanol group, blood ethanol concentrations were 137 ± 29 mg/dL at the time of feces injection and decreased to become undetectable by 12 h. Arterial hypotension occurred earlier in the ethanol than in the control group (8 [7-12] vs. 14 [11-20] hours, p = 0.03). Lactate levels increased to > 2 mmol/L earlier in the ethanol group. Renal dysfunction (9 [6-13] vs. 13 [12-15] hours, p = 0.05) and oliguria (urine output < 0.5 mL/kg/h; 10 [7-12] vs. 13 [12, 13] hours, p = 0.01) developed earlier in the ethanol than in the control group. Brain blood flow and lactate/pyruvate were unaffected. There was no significant difference in survival time.

CONCLUSIONS

Acute ethanol intoxication in this model of peritonitis resulted in earlier development of shock and renal dysfunction but did not alter brain perfusion and metabolism or short-term survival.

Effects of fenoldopam on renal blood flow in hypertensive chronic kidney disease

BACKGROUND AND AIM

The synthetic drug fenoldopam mesylate (FM) may have a renoprotective role, and a "renal dose" of 0.1 µg/kg/min intravenous (IV) infusion of FM has been reported as able to increase renal blood flow without affecting systemic blood pressure. But conclusive data are still lacking. We aimed to investigate by color-Doppler ultrasonography the effects of IV administration of FM at this dosage in hypertensive chronic kidney disease (CKD) patients, and verify whether it may induce any systemic hemodynamic alteration.

METHODS

In 60 hypertensive CKD patients, we measured by duplex Doppler ultrasonography, at baseline and during infusion of 0.1 µg/kg/min of FM, the systolic and diastolic flow velocity (sampled at the renal hilum, intermediate section and origin of both renal arteries) and the intra-parenchymal renal resistive index (RRI) sampled on interlobular arteries of both kidneys. Patients were divided into four subgroups (I-IV) according to classification of National Kidney Foundation Kidney Disease Outcomes Quality Initiative (NKF-DOQI).

RESULTS

Infusion of 0.1 µg/kg/min FM significantly decreased the RRI (0.73 ± 0.05 vs. 0.65 ± 0.06; p < 0.0001) and increased the systolic and diastolic flow velocities in all renal artery tracts examined. No single episode of systemic hypotension was observed.

CONCLUSIONS

Very low-dose FM may significantly increase renal blood flow and exert a renal protective effect in hypertensive CKD patients. Infusion of FM at such low dosage appears also to be quite safe, even in CKD and hypertensive patients.

Clopidogrel Partially Counteracts Adenosine-5'-Diphosphate Effects on Blood Pressure and Renal Hemodynamics and Excretion in Rats

BACKGROUND

Adenosine-5'-diphosphate (ADP) can influence intrarenal vascular tone and tubular transport, partly through activation of purine P2Y12 receptors (P2Y12-R), but their actual in vivo role in regulation of renal circulation and excretion remains unclear.

METHODS

The effects of intravenous ADP infusions of 2-8mg/kg/hour were examined in anesthetized Wistar rats that were untreated or chronically pretreated with clopidogrel, 20mg/kg/24hours, a selective P2Y12-R antagonist. Renal blood flow (transonic probe) and perfusion of the superficial cortex and medulla (laser-Doppler fluxes) were measured, together with urine osmolality (U_osm), diuresis (V), total solute (U_osmV), sodium (U_NaV) and potassium (U_KV) excretion.

RESULTS

ADP induced a gradual, dose-dependent 15% decrease of mean arterial pressure, a sustained increase of renal blood flow and a 25% decrease in renal vascular resistance. Clopidogrel pretreatment attenuated the mean arterial pressure decrease, and did not significantly alter renal blood flow or renal vascular resistance. Renal medullary perfusion was not affected by ADP whereas U_osm decreased from 1,080 ± 125 to 685 ± 75 mosmol/kg H₂0. There were also substantial significant decreases in U_osmV, U_NaV and U_KV; all these changes were attenuated or abolished by clopidogrel pretreatment. Two-weeks' clopidogrel treatment decreased V while U_osmU_osmV and U_NaV increased, most distinctly after 7 days. Acute clopidogrel infusion modestly decreased mean arterial pressure and significantly increased outer- and decreased inner-medullary perfusion.

CONCLUSIONS

Our functional studies show that ADP can cause systemic and renal vasodilation and a decrease in mean arterial pressure, an action at least partly mediated by P2Y12 receptors. We confirmed that these receptors exert tonic action to reduce tubular water reabsorption and urine concentration.

Renal autoregulation and blood pressure management in circulatory shock

The importance of personalized blood pressure management is well recognized. Because renal pressure–flow relationships may vary among patients, understanding how renal autoregulation may influence blood pressure control is essential. However, much remains uncertain regarding the determinants of renal autoregulation in circulatory shock, including the influence of comorbidities and the effects of vasopressor treatment. We review published studies on renal autoregulation relevant to the management of acutely ill patients with shock. We delineate the main signaling pathways of renal autoregulation, discuss how it can be assessed, and describe the renal autoregulatory alterations associated with chronic disease and with shock.

Association between exercise intensity and renal blood flow evaluated using ultrasound echo

BACKGROUND

High-intensity exercise reduces renal blood flow (RBF) and may transiently exacerbate renal dysfunction. RBF has previously been measured invasively by administration of an indicator material; however, non-invasive measurement is now possible with technological innovations. This study examined variations in RBF at different exercise intensities using ultrasound echo.

METHODS

Eight healthy men with normal renal function (eGFR_cys 114 ± 19 mL/min/1.73 m²) participated in this study. Using a bicycle ergometer, participants underwent an incremental exercise test using a ramp protocol (20 W/min) until exhaustion in Study 1 and the lactate acid breaking point (LaBP) was calculated. Participants underwent a multi-stage test at exercise intensities of 60, 80, 100, 120, and 140% LaBP in Study 2. RBF was measured by ultrasound echo at rest and 5 min after exercise in Study 1 and at rest and immediately after each exercise in Study 2. To determine the mechanisms behind RBF decline, a catheter was placed into the antecubital vein to study vasoconstriction dynamics.

RESULTS

RBF after maximum exercise decreased by 51% in Study 1. In Study 2, RBF showed no significant decrease until 80% LaBP, and showed a significant decrease (31%) at 100% LaBP compared with at rest (p < 0.01). The sympathetic nervous system may be involved in this reduction in RBF.

CONCLUSIONS

RBF showed no significant decrease until 80% LaBP, and decreased with an increase in blood lactate. Reduction in RBF with exercise above the intensity at LaBP was due to decreased cross-sectional area rather than time-averaged flow velocity.

An Ovine Model for Studying the Pathophysiology of Septic Acute Kidney Injury

The development of acute kidney injury (AKI) is both a significant and independent prognostic factor of mortality in patients with sepsis, but its pathophysiology remains unclear. Herein, we describe an ovine model of sepsis evoked by the administration of live Escherichia coli in which there is hypotension, peripheral vasodilatation with a large increase in cardiac output; a similar hyperdynamic state to that commonly reported in humans. Interestingly, in this sheep model of sepsis, despite an increase in global kidney blood flow, there is a progressive reduction in renal function. Although renal hyperperfusion develops, renal tissue hypoxia due to redistribution of intrarenal blood flow may contribute to the pathogenesis of septic AKI. We have, therefore, developed a novel methodology to chronically implant combination probes to monitor intrarenal tissue perfusion and oxygen tension during the development of septic AKI in conscious sheep with hyperdynamic sepsis.

Recent advances in the pathogenetic mechanisms of sepsis-associated acute kidney injury

Sepsis is a serious medical condition that can lead to multi-organ failure and shock, and it is associated with increased mortality. Acute kidney injury (AKI) is a frequent complication of sepsis in critically ill patients, and often requires renal replacement therapy. The pathophysiology of AKI in sepsis has not yet been fully defined. In the past, classic theories were mainly focused on systemic hemodynamic derangements, underscoring the key role of whole kidney hypoperfusion due to reduced renal blood flow. However, a growing body of experimental and clinical evidence now shows that, at least in the early phase of sepsis-associated AKI, renal blood flow is normal, or even increased. This could suggest a dissociation between renal blood flow and kidney function. In addition, the scant data available from kidney biopsies in human studies do not support diffuse acute tubular necrosis as the predominant lesion. Instead, increasing importance is now attributed to kidney damage resulting from a complex interaction between immunologic mechanisms, inflammatory cascade activation, and deranged coagulation pathways, leading to microvascular dysfunction, endothelial damage, leukocyte/platelet activation with the formation of micro-thrombi, epithelial tubular cell injury and dysfunction. Moreover, the same processes, through maladaptive responses leading to fibrosis acting from the very beginning, may set the stage for progression to chronic kidney disease in survivors from sepsis-associated AKI episodes. The aim of this narrative review is to summarize and discuss the latest evidence on the pathophysiological mechanisms involved in septic AKI, based on the most recent data from the literature.

The effects of acute renal denervation on kidney perfusion and metabolism in experimental septic shock

BACKGROUND

Perfusion deficits likely play an important role in the development of renal dysfunction in sepsis. Renal denervation may improve kidney perfusion and metabolism.

METHODS

We randomized 14 female sheep to undergo bilateral surgical renal denervation (n = 7) or sham procedure (n = 7) prior to induction of sepsis. Renal blood flow (RBF) was measured with a pre-calibrated flowprobe. Laser Doppler probes were implanted to measure cortical and medullary perfusion. Cortical glucose, lactate and pyruvate levels were measured using the microdialysis technique. Creatinine clearance was determined. Sepsis was induced by peritonitis and fluid resuscitation was provided to avoid hypovolemia.

RESULTS

RBF and cortical perfusion were higher in the denervated group during the first 6 h after induction of sepsis (P < 0.001 and P < 0.05, respectively), while medullary perfusion decreased similarly in both groups. After hypotension developed, RBF decreased to similar levels in both groups. Cortical pyruvate and lactate levels were lower in the denervated animals (P < 0.001 and P < 0.001, respectively). There were no differences between groups in creatinine clearance, urine output or time to oliguria.

CONCLUSION

Denervation thus caused an early increase in RBF that was distributed towards the kidney cortex. Although associated with an attenuation of early cortical metabolic alterations, denervation failed to prevent the deterioration in renal function.

Acute kidney injury in the ICU: from injury to recovery: reports from the 5th Paris International Conference

The French Intensive Care Society organized its yearly Paris International Conference in intensive care on June 18-19, 2015. The main purpose of this meeting is to gather the best experts in the field in order to provide the highest quality update on a chosen topic. In 2015, the selected theme was: "Acute Renal Failure in the ICU: from injury to recovery." The conference program covered multiple aspects of renal failure, including epidemiology, diagnosis, treatment and kidney support system, prognosis and recovery together with acute renal failure in specific settings. The present report provides a summary of every presentation including the key message and references and is structured in eight sections: (a) diagnosis and evaluation, (b) old and new diagnosis tools,

Acute kidney injury in the ICU: from injury to recovery: reports from the 5th Paris International Conference

The French Intensive Care Society organized its yearly Paris International Conference in intensive care on June 18-19, 2015. The main purpose of this meeting is to gather the best experts in the field in order to provide the highest quality update on a chosen topic. In 2015, the selected theme was: "Acute Renal Failure in the ICU: from injury to recovery." The conference program covered multiple aspects of renal failure, including epidemiology, diagnosis, treatment and kidney support system, prognosis and recovery together with acute renal failure in specific settings. The present report provides a summary of every presentation including the key message and references and is structured in eight sections: (a) diagnosis and evaluation, (b) old and new diagnosis tools,

Renal function and oxygenation are impaired early after liver transplantation despite hyperdynamic systemic circulation

Background

Acute kidney injury (AKI) occurs frequently after liver transplantation and is associated with the development of chronic kidney disease and increased mortality. There is a lack of data on renal blood flow (RBF), oxygen consumption, glomerular filtration rate (GFR) and renal oxygenation, i.e. the renal oxygen supply/demand relationship, early after liver transplantation. Increased insight into the renal pathophysiology after liver transplantation is needed to improve the prevention and treatment of postoperative AKI. We have therefore studied renal hemodynamics, function and oxygenation early after liver transplantation in humans.

Methods

Systemic hemodynamic and renal variables were measured during two 30-min periods in liver transplant recipients (n = 12) and post-cardiac surgery patients (controls, n = 73). RBF and GFR were measured by the renal vein retrograde thermodilution technique and by renal extraction of Cr-EDTA (= filtration fraction), respectively. Renal oxygenation was estimated from the renal oxygen extraction.

Results

In the liver transplant group, GFR decreased by 40% (p < 0.05), compared to the preoperative value. Cardiac index and systemic vascular resistance index were 65% higher (p < 0.001) and 36% lower (p < 0.001), respectively, in the liver transplant recipients compared to the control group. GFR was 27% (p < 0.05) and filtration fraction 40% (p < 0.01) lower in the liver transplant group. Renal vascular resistance was 15% lower (p < 0.05) and RBF was 18% higher (p < 0.05) in liver transplant recipients, but the ratio between RBF and cardiac index was 27% lower (p < 0.001) among the liver-transplanted patients compared to the control group. Renal oxygen consumption and extraction were both higher in the liver transplants, 44% (p < 0.01) and 24% (p < 0.05) respectively.

Conclusions

Despite the hyperdynamic systemic circulation and renal vasodilation, there is a severe decline in renal function directly after liver transplantation. This decline is accompanied by an impaired renal oxygenation, as the pronounced elevation of renal oxygen consumption is not met by a proportional increase in renal oxygen delivery. This information may provide new insights into renal pathophysiology as a basis for future strategies to prevent/treat AKI after liver transplantation.

Trial registration

ClinicalTrials.gov, NCT02455115. Registered on 23 April 2015.

Effect of nitric oxide on renal autoregulation during hypothermia in the rat

Hypothermia-induced reduction of metabolic rate is accompanied by depression of both glomerular perfusion and filtration. The present study investigated whether these changes are linked to changes in renal autoregulation and nitric oxide (NO) signalling. During hypothermia, renal blood flow (RBF) and glomerular filtration rate (GFR) were reduced and urine production was increased, and this was linked with reduced plasma cGMP levels and increased renal vascular resistance. Although stimulation of NO production decreased vascular resistance, blood pressure and urine flow, intravenous infusion of the NO precursor L-arginine or the NO donor sodium nitroprusside did not alter RBF or GFR. In contrast, inhibition of NO synthesis by N^w-nitro-L-arginine led to a further decline in both parameters. Functional renal autoregulation was apparent at both temperatures. Below the autoregulatory range, RBF in both cases increased in proportion to the perfusion ±pressure, although, the slope of the first ascending limb of the pressure-flow relationship was lower during hypothermia. The main difference was rather that the curves obtained during hypothermia levelled off already at a RBF of 3.9 ± 0.3 mL/min then remained stable throughout the autoregulatory pressure range, compared to 7.6 ± 0.3 mL/min during normothermia. This was found to be due to a threefold increase in, primarily, the afferent arteriolar resistance from 2.6 to 7.5 mmHg min mL⁻¹. Infusion of sodium nitroprusside did not significantly affect RBF during hypothermia, although a small increase at pressures below the autoregulatory range was observed. In conclusion, cold-induced rise in renal vascular resistance results from afferent arteriolar vasoconstriction by the autoregulatory mechanism, setting RBF and GFR in proportion to the metabolic rate, which cannot be explained by reduced NO production alone.

Advances in the non-invasive assessment of vascular dysfunction in metabolic syndrome and diabetes: Focus on endothelium, carotid mechanics and renal vessels

AIM

The present paper is a selective review on the methodology and clinical significance of techniques to assess specifically endothelial function, carotid mechanics and renal vascular function, particularly in the light of vascular dysfunction in metabolic syndrome and type 2 diabetes.

DATA SYNTHESIS

Endothelial dysfunction appears to be earlier detectable in the microcirculation of patients with altered glucose metabolism, while it attains significance in the macrocirculation at more advanced disease stages. Smooth muscle cell dysfunction is now increasingly recognized to play a role both in the development of endothelial dysfunction and abnormal arterial distensibility. Furthermore, impaired glucose metabolism affects carotid mechanics through medial calcification, structural changes in extracellular matrix due to advanced glycation and modification of the collagen/elastin material stiffness. The assessment of renal vascular function by dynamic ultrasound or magnetic resonance imaging has recently emerged as an appealing target for identifying subtle vascular alterations responsible for the development of diabetic nephropathy.

CONCLUSIONS

Vascular dysfunction represents a major mechanism for the development of cardiovascular disease in patients with abnormal glucose metabolism. Hence, the currently available non-invasive techniques to assess early structural and vascular abnormalities merit recommendation in this population, although their predictive value and sensitivity to monitor treatment-induced changes have not yet been established and are still under investigation.

Changes in kidney perfusion and renal cortex metabolism in septic shock: an experimental study

BACKGROUND

The etiology of renal dysfunction in sepsis is currently attributed to altered perfusion, microcirculatory abnormalities and cellular alterations. To clarify these mechanisms, we characterized the changes in renal perfusion and cortex metabolism in a large animal model of sepsis.

METHODS

We studied 12 adult female sheep randomized to peritonitis-induced sepsis (n = 8) or to sham procedure (n = 4). A flow probe was positioned around the renal artery to measure renal blood flow (RBF). Laser Doppler was used to measure regional flow in the kidney cortex and medulla. A microdialysis probe was inserted into the renal cortex to measure cortical glucose, lactate, and pyruvate. Fluid resuscitation was provided to keep pulmonary artery occlusion pressure at baseline levels. All animals were observed for 18 h.

RESULTS

Hypotension occurred after 9 h in the septic animals (P = 0.02 versus baseline). RBF and cortical flow were significantly lower than at baseline from 12 h in the septic animals (P = 0.01 and P = 0.03, respectively). Cortical lactate and pyruvate levels increased in the septic animals from 3 and from 6 h, respectively (both P = 0.02 versus baseline), and the L/P ratio from 15 h (P = 0.01). There was a correlation between cortical flow and cortical L/P ratio after shock onset (r = -0.60, P = 0.002) but not before.

CONCLUSIONS

In this peritonitis model, sepsis was associated with metabolic alterations that may reflect early induction of cortical glycolysis. Septic shock was associated with reduced renal perfusion and decreased cortical and medullary blood flow, followed by signs of anaerobic metabolism in the cortex when flow reductions became critical.