Renal clearance of endogenous creatinine and urea in sheep during summer and winter

Preclinical septic shock research: why we need an animal ICU

Animal experiments are widely used in preclinical medical research with the goal of disease modeling and exploration of novel therapeutic approaches. In the context of sepsis and septic shock, the translation into clinical practice has been disappointing. Classical animal models of septic shock usually involve one-sex-one-age animal models, mostly in mice or rats, contrasting with the heterogeneous population of septic shock patients. Many other factors limit the reliability of preclinical models and may contribute to preclinical research failure in critical care, including the host specificity of several pathogens, the fact that laboratory animals are raised in pathogen-free facilities and that organ support techniques are either absent or minimal. Advanced animal models have been developed with the aim of improving the clinical translatability of experimental findings. So-called animal ICUs refer to the preclinical investigation of adult or even aged animals of either sex, using—in case of rats and mice—miniaturized equipment allowing for reproducing an ICU environment at a small animal scale and integrating chronic comorbidities to more closely reflect the clinical conditions studied. Strength and limitations of preclinical animal models designed to decipher the mechanisms involved in septic cardiomyopathy are discussed. This article reviews the current status and the challenges of setting up an animal ICU.

Structure and Function of the Kidney in Septic Shock. A Prospective Controlled Experimental Study

RATIONALE

It is unclear how septic shock causes acute kidney injury (AKI) and whether this is associated with histological change.

OBJECTIVES

We aimed to determine the nature and extent of changes in renal structure and function over time in an ovine model of septic shock.

METHODS

Fifteen sheep were instrumented with a renal artery flow probe and renal vein cannula. Ten were given intravenous Escherichia coli to induce septic shock, and five acted as controls. Animals were mechanically ventilated for 48 hours, while receiving protocol-guided parenteral fluids and a norepinephrine infusion to maintain mean arterial pressure. Renal biopsies were taken every 24 hours or whenever animals were oliguric for 2 hours. A renal pathologist, blinded to tissue source, systematically quantified histological appearance by light and electron microscopy for 31 prespecified structural changes.

MEASUREMENTS AND MAIN RESULTS

Sheep given E. coli developed septic shock, oliguria, increased serum creatinine, and reduced creatinine clearance (AKI), but there were no changes over time in renal blood flow between groups (P > 0.30) or over time within groups (P > 0.50). Renal oxygen consumption increased only in nonseptic animals (P = 0.01), but there was no between-group difference in renal lactate flux (P > 0.50). There was little structural disturbance in all biopsies and, although some cellular appearances changed over time, the only difference between septic and nonseptic animals was mesangial expansion on electron microscopy.

CONCLUSIONS

In an intensive care-supported model of gram-negative septic shock, early AKI was not associated with changes in renal blood flow, oxygen delivery, or histological appearance. Other mechanisms must contribute to septic AKI.

Evaluation of haemodialysis as a protective technique for preventing high daily dose amikacin nephrotoxicity: an experimental study in an ovine model

Changes in pharmacokinetic parameters of critically ill patients make the treatment of infections challenging, particularly when multidrug-resistant bacteria are involved. The aim of this study was to evaluate the ability of haemodialysis to reduce the exposure to high dose amikacin and prevent nephrotoxicity. Amikacin 50 mg/kg was administered intravenously to six adult sheep once-daily for four days. The sheep were divided into two groups according to the implementation (group 1) or not (group 2) of haemodialysis. In group 1, haemodialysis was performed for 4 h, initiated 2 h after starting amikacin infusion. Amikacin area under the curve (AUC) and trough concentrations (C_min) were used as markers of amikacin-induced nephrotoxicity. The median haemodialysis amikacin clearance was 2.14 L/h (35.6 mL/min), 14% of the mean total body clearance for 24 h. Haemodialysis reduced C_min (group 1: 0.3 µg/mL [0.3-1.1]; group 2: 1.4 µg/mL [1.1-3.9]; P = 0.0003). A trend towards reduced AUC with haemodialysis was observed (group 1: 1450 µg/mL⋅h [1311-1716]; group 2: 3126 µg/mL⋅h [2581-3171]; P = 0.10). In conclusion, haemodialysis seems interesting in reducing AUC and C_min after the injection of high-dose of amikacin, parameters known to be involved in its induced nephrotoxicity, in an experimental ovine model.

Renal effects of treatment with a TLR4 inhibitor in conscious septic sheep

Introduction

Acute kidney injury (AKI) is a common and feared complication of sepsis. The pathogenesis of sepsis-induced AKI is largely unknown, and therapeutic interventions are mainly supportive. In the present study, we tested the hypothesis that pharmacological inhibition of Toll-like receptor 4 (TLR4) would improve renal function and reduce renal damage in experimental sepsis, even after AKI had already developed.

Methods

Sheep were surgically instrumented and subjected to a 36-hour intravenous infusion of live Escherichia coli. After 12 hours, they were randomized to treatment with a selective TLR4 inhibitor (TAK-242) or vehicle.

Results

The E. coli caused normotensive sepsis characterized by fever, increased cardiac index, hyperlactemia, oliguria, and decreased creatinine clearance. TAK-242 significantly improved creatinine clearance and urine output. The increase in N-acetyl-beta-D-glucosaminidas, a marker of tubular damage, was attenuated. Furthermore, TAK-242 reduced the renal neutrophil accumulation and glomerular endothelial swelling caused by sepsis. These effects were independent of changes in renal artery blood flow and renal microvascular perfusion in both cortex and medulla. TAK-242 had no effect per se on the measured parameters.

Conclusions

These results show that treatment with a TLR4 inhibitor is able to reverse a manifest impairment in renal function caused by sepsis. In addition, the results provide evidence that the mechanism underlying the effect of TAK-242 on renal function does not involve improved macro-circulation or micro-circulation, enhanced renal oxygen delivery, or attenuation of tubular necrosis. TLR4-mediated inflammation resulting in glomerular endothelial swelling may be an important part of the pathogenesis underlying Gram-negative septic acute kidney injury.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-014-0488-y) contains supplementary material, which is available to authorized users.

Renal function changes and seasonal temperature in patients undergoing cardiac surgery

Some observations in humans and other mammalians suggest that serum creatinine (SC) and estimated glomerular filtration rate (eGFR) may change during the warm season. The objective of this study is to determine if temperature-dependent seasonal changes in levels of SC and eGFR are detectable in cardiac surgery patients, with associated changes in postoperative acute kidney injury (AKI) incidence. This is a single-center retrospective study based on the institutional database of cardiac surgery in the period 2000-2012. Sixteen-thousand and twenty-three consecutive adult patients undergoing cardiac surgery comprised the study population. Baseline and postoperative SC and eGFR values, and AKI rate according to the month when surgery was performed were measured. The month-related changes SC and eGFR, and AKI rate, were assessed in crude and adjusted models, and their association with the correspondent meteorological data registered at the time of surgery was tested. Patients operated in the six warmest months (May through October) had a significant (p < 0.001) higher value of baseline SC (1.17 ± 0.7 mg/dL) versus the six coldest months (1.12 ± 0.6 mg/dL), and a significantly (p = 0.031) higher value of peak postoperative SC (1.31 ± 0.85 mg/dL) versus the 6 coldest months (1.28 ± 0.89), with maximum values between July and August. A similar behaviour was found for eGFR. After adjustment for other confounders, the AKI rate was not significantly different in the warmest months, even if a trend towards a higher rate in August was observed (odds ratio 1.287, 95% confidence interval 0.96-1.74, p = 0.097). Baseline (p < 0.001) and peak postoperative (p = 0.0054) serum creatinine levels were significantly higher for increasing mean ambient temperature. Humidity and wind speed were negatively associated with pre- and postoperative eGFR. In conclusion, patients operated during the warmest season, have higher levels of SC and lower levels of eGFR, without a correspondent increase in the AKI rate. Different hypotheses underlying this pattern are generated by this study, including a dehydration status, concomitant anemia, and a higher transfusion rate.

New insights into urea and glucose handling by the kidney, and the urine concentrating mechanism

The mechanism by which urine is concentrated in the mammalian kidney remains incompletely understood. Urea is the dominant urinary osmole in most mammals and may be concentrated a 100-fold above its plasma level in humans and even more in rodents. Several facilitated urea transporters have been cloned. The phenotypes of mice with deletion of the transporters expressed in the kidney have challenged two previously well-accepted paradigms regarding urea and sodium handling in the renal medulla but have provided no alternative explanation for the accumulation of solutes that occurs in the inner medulla. In this review, we present evidence supporting the existence of an active urea secretion in the pars recta of the proximal tubule and explain how it changes our views regarding intrarenal urea handling and UT-A2 function. The transporter responsible for this secretion could be SGLT1, a sodium-glucose cotransporter that also transports urea. Glucagon may have a role in the regulation of this secretion. Further, we describe a possible transfer of osmotic energy from the outer to the inner medulla via an intrarenal Cori cycle converting glucose to lactate and back. Finally, we propose that an active urea transporter, expressed in the urothelium, may continuously reclaim urea that diffuses out of the ureter and bladder. These hypotheses are all based on published findings. They may not all be confirmed later on, but we hope they will stimulate further research in new directions.

Renal phosphate excretion in goats

It was the aim of these experiments to characterize further the role of salivary glands and kidneys in phosphate (Pi) homeostasis of small ruminants. Renal clearance experiments were performed in five female, non-pregnant adult goats during infusions of physiological NaCl or isotonic phosphate solution. Basal plasma Pi concentrations of 1.6 +/- 0.3 mM (NaCl infusion) were associated with a renal resorption of the filtered Pi by 98.5-99.3% and Pi was excreted in the urine at a rate of 1.2-2.8 mumol/min. Elevating the plasma Pi levels up to 7.2 +/- 1.7 mM resulted in significant increases of Pi excretion. The mean plasma threshold for renal Pi excretion of these animals was high (4.3 +/- 1.0 mM) and thus substantially higher than the physiological range of plasma Pi. The maximal tubular resorption rate for Pi in goats was found to be higher than the respective values in monogastric animals. In relation to the enhanced Pi concentrations in plasma the salivary Pi concentrations increased simultaneously and reached a maximum level of about 66.3 mM at plasma levels between 4-6 mM. Indications for hormonal regulation mechanisms via parathyroid hormone (PTH) and calcitriol could not be detected during the infusion periods.

Influences of season and of temperature, photoperiod, and subcutaneous melatonin infusion on the glomerular filtration rate of ewes

Influences of season and of temperature, photoperiod, and subcutaneous melatonin infusion on glomerular filtration rate (GFR) were measured in ewes. There was a seasonal difference of GFR between summer (June-August) and winter (December-February) in Tokyo (35 degrees, 35' N); GFR was significantly (P < 0.05) higher in summer (4.2 +/- 0.3 ml/min/kg) than in winter (3.0 +/- 0.2 ml/min/kg). GFR was measured after exposure to three types of photoperiod, 24L:0D, 12L:12D, and 0L:24D, for 7 to 8 days. The value for GFR obtained at 20 degrees C was significantly lower (P < 0.05) with 0L:24D than with the other two photoperiodic conditions. GFR obtained during subcutaneous melatonin infusion (20 micrograms/hr for 16 hr/day for 7 days) with 24L:0D conditions was significantly (P < 0.05) lower (2.5 +/- 0.1 ml/min/kg) than without infusion (3.8 +/- 0.3 ml/min/kg) and was about the same as that obtained in animals under 0L:24D conditions. At 30 degrees C, GFR exhibited no difference between the 3 photoperiodic conditions and was always lower than that found at 20 degrees C. Possible influences of melatonin on GFR are discussed.

Water and electrolyte homeostasis in sheep without functional colons

The regulatory role of the colon in water and electrolyte balance and the renal compensation which follows impairment of colonic function were assessed using sheep with ileorectal anastomosis (ILRAN sheep) on restricted and free water intake as experimental models. Faecal electrolyte loss sustained by the ILRAN group was eight to nine times greater than that in the control animals. When water was available ad lib., ILRAN sheep lost 2.81 and 0.51 more water per day via the faeces and urine, respectively, than the controls. Urine volume in the ILRAN sheep comprised largely electrolyte-free water and the renal retention of water was entirely secondary to the high degree of sodium reabsorption in these animals compared with the controls. On restricted water intake, the urine volume of the ILRAN sheep declined due to retention of electrolyte-free water and even greater absorption of sodium (and hence water by osmosis) by the kidney tubules. The latter observation was substantiated by a decrease in fractional excretion of sodium from 0.29 to 0.08% when water intake was restricted. Plasma aldosterone concentration was markedly elevated in the ILRAN sheep as a result of the excessive loss of sodium and water via the faeces. Activation of the renin-angiotensin-aldosterone sequence is believed to underlie the increased sensation of thirst (ILRAN sheep drank on average about 2.51 more water per day than the controls), the homeostatic response by the kidneys and the relatively lower plasma potassium in the ILRAN sheep compared to controls.

Renovascular interaction of epinephrine, dopamine, and intraperitoneal sepsis

OBJECTIVE

To determine the effect of intraperitoneal sepsis on the systemic and renal actions of the continous infusion of epinephrine or dopamine, and during the concurrent administration of both drugs.

DESIGN

Prospective, randomized study.

SETTING

Laboratory at a university hospital.

SUBJECTS

Seven conscious, chronically catheterized, adult merino sheep.

INTERVENTIONS

Epinephrine at 40 micrograms/min or dopamine at 2 micrograms/kg/min, or both drugs concurrently were infused for 4 hrs on separate study days in healthy sheep. This protocol was then repeated following the induction of sepsis after the intraperitoneal injection of 10(11) Escherichia coli, 10(12) Bacteroides fragilis, and bran.

MEASUREMENTS AND MAIN RESULTS

Systemic oxygen delivery (DO2) and consumption were measured using thermodilution cardiac output and measured oxygen content. Renal blood flow was measured using an electromagnetic flow transducer, and creatinine clearance was calculated as the quotient of renal blood flow and the renal extraction ratio of creatinine. Infusion of epinephrine augmented systemic DO2 and mean arterial pressure (MAP) during both healthy and septic studies. Systemic oxygen consumption was only increased during epinephrine infusion in the septic study. During the healthy animal study, renal blood flow was initially decreased during epinephrine infusion, but increased to 36% above baseline (p = .003). However, creatinine clearance remained unchanged. During the experimental sepsis study, the infusion of epinephrine had less marked effects on renal blood flow (unchanged from baseline), while an initial reduction (15 mins) in creatinine clearance (p = .04) was not sustained and had returned to baseline by 3 hrs. Dopamine alone produced no change in systemic oxygen variables or MAP during the studies on healthy or septic animals. Although dopamine produced renal vasodilation and an increase in renal blood flow in the healthy state, these results were not found during the septic state. In addition, concurrent infusion of dopamine with epinephrine did not alter the systemic or renal effects of epinephrine during the healthy or septic states.

CONCLUSIONS

These results do not support the routine use of low-dose dopamine, and demonstrate a change in renovascular responses to catecholamines during intraperitoneal sepsis. The infusion of epinephrine at 40 micrograms/min had few deleterious effects on the kidney, and augmented both MAP and systemic DO2. Its role as a catecholamine in the management of sepsis may need to be reconsidered.

Disposition kinetics, renal clearance and excretion of ampicillin after oral administration in goats

Disposition kinetics, renal clearance and urinary excretion of ampicillin were determined after oral administration of 10 mg/kg in 8 goats. Peak plasma concentration 1.86 +/- 0.14 mumol/l was attained at 117 +/- 11 min after oral administration. Half-time of absorption was 28.7 +/- 5.8 minutes and that of elimination was 135 +/- 15 minutes. Total area under plasma concentration versus time curve was 9.16 +/- 0.97 mumol.h/l. Total body clearance of ampicillin was 52.1 +/- 4.2 and renal clearance was 0.07 +/- 0.008 ml/min.kg. The renal handling of ampicillin involved glomerular filtration and back diffusion.