Perfusion pressure dependency of in vivo renal tubular dynamics

Establishment and evaluation of a reversible two-kidney, one-clip renovascular hypertensive rat model

The aim of the present study was to establish and evaluate a novel and reversible two-kidney, one-clip renovascular hypertensive rat model with a titanium vascular clip. A total of 40 male Sprague-Dawley rats were evenly and randomly divided into a sham-operated group, and 3, 7, 12 and 28D groups (namely removing the vascular clip in the renovascular hypertensive model after 3, 7, 12 and 28 days, respectively). The systolic blood pressure (SBP) and plasma renin activity (PRA) were measured, and color duplex imaging was conducted before placing the clips, as well as before and after removing them. After placing the vascular clips, SBP and PRA in the 3, 7, 12 and 28D groups were significantly increased (SBP: Sham-operated vs. 3D groups, P=0.020; 3 vs. 7D groups, P=0.008; 7 vs. 28D groups, P=0.019; 12 vs. 28D groups, P=0.039, and between other groups P<0.001. PRA: 3 vs. 7D groups, P=0.001; 7 vs. 12D groups, P=0.004; 12 vs. 28D groups, P=0.040, and between other groups, P<0.001). After removing the clips, SBP were significantly reduced in the 3 and 7D groups (P=0.023, 0.040, 0.066 and 0.314 in the 3, 7, 12 and 28D groups, respectively), but were still significantly higher than that before placing clips in the 7, 12 and 28D groups (P=0.067, P=0.005, P<0.001 and P<0.001 in the 3, 7, 12 and 28D groups, respectively). After removing the clips, PRA was significantly reduced in each group (P<0.001, P<0.001, P=0.012 and P=0.049 in 3, 7, 12 and 28D groups, respectively), but still higher than that before placing the clips (P<0.001, P=0.001, P=0.001 and P=0.003 in 3, 7, 12 and 28D groups, respectively). Vascular imaging also indicates this model has a reversible property. In conclusion, a reversible renovascular hypertension rat model is feasible, and provides a basis for research on clinical ischemic nephropathy and renal artery revascularization.

An Official ATS/ERS/ESICM/SCCM/SRLF Statement: Prevention and Management of Acute Renal Failure in the ICU Patient: an international consensus conference in intensive care medicine

OBJECTIVES

To address the issues of Prevention and Management of Acute Renal Failure in the ICU Patient, using the format of an International Consensus Conference.

METHODS AND QUESTIONS

Five main questions formulated by scientific advisors were addressed by experts during a 2-day symposium and a Jury summarized the available evidence: (1) Identification and definition of acute kidney insufficiency (AKI), this terminology being selected by the Jury; (2) Prevention of AKI during routine ICU Care; (3) Prevention in specific diseases, including liver failure, lung Injury, cardiac surgery, tumor lysis syndrome, rhabdomyolysis and elevated intraabdominal pressure; (4) Management of AKI, including nutrition, anticoagulation, and dialysate composition; (5) Impact of renal replacement therapy on mortality and recovery.

RESULTS AND CONCLUSIONS

The Jury recommended the use of newly described definitions. AKI significantly contributes to the morbidity and mortality of critically ill patients, and adequate volume repletion is of major importance for its prevention, though correction of fluid deficit will not always prevent renal failure. Fluid resuscitation with crystalloids is effective and safe, and hyperoncotic solutions are not recommended because of their renal risk. Renal replacement therapy is a life-sustaining intervention that can provide a bridge to renal recovery; no method has proven to be superior, but careful management is essential for improving outcome.

Acute angiotensin II infusions elicit pressure natriuresis in mice and reduce distal fractional sodium reabsorption

Acute angiotensin II (Ang II) infusions into mice increase arterial pressure (AP) and elicit pressure natriuresis. We used this model of pressure natriuresis to delineate the distal nephron responses to AP-mediated increases in distal sodium delivery. In the first group, we measured changes in urinary sodium excretion (U(Na)V) in male C57/BL6 anesthetized mice (n=9) before and during acute Ang II infusions (5 ng/g of body weight per minute). Acute Ang II infusions increased AP (98+/-3 to 126+/-5 mm Hg; P<0.001), urine flow (2.7+/-0.5 to 6.0+/-0.8 microL/min; P<0.01), and U(Na)V (0.6+/-0.2 to 1.3+/-0.2 microEq/min; P<0.05). There were significant relationships between U(Na)V and urine flow (y=0.207x+0.030; P<0.0001) and between U(Na)V and AP (y=0.027x-2.100). In a separate series, distal sodium delivery and fractional reabsorption of distal sodium delivery were determined in control (n=12) and Ang II-infused mice (n=8) by comparing U(Na)V before and after blockade of the 2 major distal nephron sodium transporters with amiloride (5 mg/kg of body weight) plus bendroflumethiazide (12 mg/kg of body weight). A positive relationship was found between U(Na)V (y=0.015x-1.100; P<0.0001) or distal sodium delivery (y=0.027x-0.900; P<0.0001) and AP. An inverse relationship was found between fractional reabsorption of distal sodium delivery and AP (y=-0.511x+128.300; P<0.01). These data indicate that Ang II-mediated pressure natriuresis involves an increase in distal sodium delivery combined with a reduced distal nephron fractional sodium reabsorption, suggesting that increased AP prevents the distal nephron transport mechanisms from accommodating the increased distal delivery.

Noninvasive measurement of concurrent single-kidney perfusion, glomerular filtration, and tubular function

To assess the reliability of electron beam computed tomography (EBCT), measurements of single-kidney renal blood flow (RBF), glomerular filtration rate (GFR), and intratubular contrast medium concentration (ITC) of radiographic contrast media were quantified in anesthetized pigs before and after acetylcholine-induced vasodilation and diuresis. EBCT measurements were compared with those obtained with intravascular Doppler and inulin clearance. The capability of EBCT to detect chronic changes in single-kidney function was evaluated in pigs with unilateral renal artery stenosis, and their long-term reproducibility in normal pigs was studied repeatedly at 1-mo intervals. EBCT-RBF (ml/min) correlated with Doppler-RBF as RBF(EBCT) = 45 + 1.07 * RBF(Doppler), r = 0.81. EBCT-GFR (ml/min) correlated with inulin clearance as GFR(EBCT) = 11.7 + 1.02 * GFR(inulin), r = 0.80. During vasodilation, RBF and GFR increased, whereas ITC decreased along the nephron. In renal artery stenosis, single-kidney GFR decreased linearly with the degree of stenosis, and ITC increased along the nephron, indicating increased fluid reabsorption. EBCT-RBF, GFR, and ITC were similar among repeated measurements. This approach might be invaluable for simultaneous quantification of regional hemodynamics and function in the intact kidneys, in a manner potentially applicable to humans.