Effects of anesthetics on the kidney

The Development of a Juvenile Porcine Augmented Renal Clearance Model Through Continuous Infusion of Lipopolysaccharides: An Exploratory Study

Augmented renal clearance (ARC) as observed in the critically ill (pediatric) population can have a major impact on the pharmacokinetics and posology of renally excreted drugs. Although sepsis has been described as a major trigger in the development of ARC in human critically ill patients, mechanistic insights on ARC are currently lacking. An appropriate ARC animal model could contribute to reveal these underlying mechanisms. In this exploratory study, a state of ARC was induced in 8-week-old piglets. Conscious piglets were continuously infused over 36 h with lipopolysaccharides (LPS) from Escherichia coli (O111:B4) to induce sepsis and subsequently trigger ARC. To study the dose-dependent effect of LPS on the renal function, three different doses (0.75, 2.0, 5.0 μg/kg/h) were administered (two ♂ piglets/dose, one sham piglet), in combination with fluid administration (0.9% NaCl) at 6 ml/kg/h. Single boluses of renal markers, i.e., creatinine [40 mg/kg body weight (BW)], iohexol (64.7 mg/kg BW), and para-aminohippuric acid (PAH, 10 mg/kg BW) were administered intravenously to evaluate the effect of LPS on the renal function. Clinical parameters were monitored periodically. Blood sampling was performed to determine the effect on hematology, neutrophil gelatinase-associated lipocalin, and prostaglandin E₂ plasma levels. All piglets that were continuously infused with LPS displayed an elevated body temperature, heart rhythm, and respiratory rate ~1-3 h after start of the infusion. After infusion, considerably higher total body clearances of iohexol, creatinine, and PAH were observed, independent of the administration of LPS and/or its dose. Since also the sham piglet, receiving no LPS, demonstrated a comparable increase in renal function, the contribution of fluid administration to the development of ARC should be further evaluated.

Conventional Pig as Animal Model for Human Renal Drug Excretion Processes: Unravelling the Porcine Renal Function by Use of a Cocktail of Exogenous Markers

Over recent years, pigs have been promoted as potential animal model due to their anatomical and physiological similarities with humans. However, information about the contribution of distinct renal elimination processes [glomerular filtration rate (GFR), effective renal plasma flow (ERPF), tubular secretion, and reabsorption] in pigs is currently limited. Therefore, a cocktail of renal markers, consisting of iohexol (GFR), para-aminohippuric acid (ERPF and net tubular anion secretion), pindolol (net tubular cation secretion), and fluconazole (net tubular reabsorption) was administered intravenously to 7-week-old male conventional pigs. Plasma and urinary concentrations were determined using validated analytical methods. The clearance of iohexol (GFR) was 97.87 ± 16.05 ml/min/m² (mean ± SD). The ERPF, calculated as the renal clearance of PAH, was 226.77 ± 62.45 ml/min/m², whereas the net tubular secretion of PAH was 130.28 ± 52.62 ml/min/m². The net tubular secretion of R-pindolol and S-pindolol was 13.53 ± 12.97 and 18.01 ± 39.23 ml/min/m², respectively. The net tubular reabsorption of fluconazole was 78.32 ± 13.52 ml/min/m². Overall, this cocktail of renal markers was considered to be safe for use in pigs since no adverse effects were observed. Iohexol, PAH and fluconazole were considered suitable renal marker to assess the porcine renal function. Pindolol seems less appropriate due to the high degree of nonrenal clearance in pigs. The values of GFR, ERPF, and anion secretion are within the same range for both human and pig. Regarding the tubular reabsorption of fluconazole, slightly higher values were obtained for pigs. Nevertheless, these results indicate the conventional pig could be an appropriate animal model to study renal drug elimination processes in humans.

N-acetylcysteine protects against star fruit-induced acute kidney injury

Background: Star fruit (SF) is a popular fruit, commonly cultivated in many tropical countries, that contains large amount of oxalate. Acute oxalate nephropathy and direct renal tubular damage through release of free radicals are the main mechanisms involved in SF-induced acute kidney injury (AKI). The aim of this study was to evaluate the protective effect of N-acetylcysteine (NAC) on SF-induced nephrotoxicity due to its potent antioxidant effect.

Materials and methods: Male Wistar rats received SF juice (4 mL/100 g body weight) by gavage after a 12 h fasting and water deprivation. Fasting and water deprivation continued for 6 h thereafter to warrant juice absorption. Thereafter, animals were allocated to three experimental groups: SF (n = 6): received tap water; SF + NAC (n = 6): received NAC (4.8 g/L) in drinking water for 48 h after gavage; and Sham (n = 6): no interventions. After 48 h, inulin clearance studies were performed to determine glomerular filtration rate. In a second series of experiment, rats were housed in metabolic cages for additional assessments.

Results: SF rats showed markedly reduced inulin clearance associated with hyperoxaluria, renal tubular damage, increased oxidative stress and inflammation. NAC treatment ameliorated all these alterations. Under polarized light microscopy, SF rats exhibited intense calcium oxalate birefringence crystals deposition, dilation of renal tubules and tubular epithelial degeneration, which were attenuate by NAC therapy.

Conclusions: Our data show that therapeutic NAC attenuates renal dysfunction in a model of acute oxalate nephropathy following SF ingestion by reducing oxidative stress, oxaluria, and inflammation. This might represent a novel indication of NAC for the treatment of SF-induced AKI.

Blood volume, blood pressure and total body sodium: internal signalling and output control

Total body sodium and arterial blood pressure (ABP) are mutually dependent variables regulated by complex control systems. This review addresses the role of ABP in the normal control of sodium excretion (NaEx), and the physiological control of renin secretion. NaEx is a pivotal determinant of ABP, and under experimental conditions, ABP is a powerful, independent controller of NaEx. Blood volume is a function of dietary salt intake; however, ABP is not, at least not in steady states. A transient increase in ABP after a step-up in sodium intake could provide a causal relationship between ABP and the regulation of NaEx via a hypothetical integrative control system. However, recent data show that subtle sodium loading (simulating salty meals) causes robust natriuresis without changes in ABP. Changes in ABP are not necessary for natriuresis. Normal sodium excretion is not regulated by pressure. Plasma renin is log-linearly related to salt intake, and normally, decreases in renin secretion are a precondition of natriuresis after increases in total body sodium. Renin secretion is controlled by renal ABP, renal nerve activity and the tubular chloride concentrations at the macula densa (MD). Renal nerve activity is related to blood volume, also at constant ABP, and elevates renin secretion by means of beta(1)-adrenoceptors. Recent results indicate that renal denervation reduces ABP and renin activity, and that sodium loading may decrease renin without changes in ABP, glomerular filtration rate or beta(1)-mediated nerve activity. The latter indicates an essential role of the MD mechanism and/or a fourth mediator of the physiological control of renin secretion.

The physiology of nutritional assessment and therapy in protein-calorie malnutrition

Protein-calorie malnutrition (PCM), in the purest sense, is the result of depleted body protein stores due to semistarvation. A review of the hormonal response to simple semistarvation illustrates the elegant adaptive ability of the body to respond to an inadequate diet. By contrast, the body's metabolic response to an injury or illness stimulus is a dynamic process orchestrated by monokines and hormones. Although the injury response, strictly speaking, is not synonymous with PCM, the resultant increased energy expenditure, anorexia, and potential for skeletal muscle breakdown can result in an even more rapid depletion of body protein stores. Ultimately, the need for nutritional support depends on the amount of recent weight loss, anticipated time of insufficient oral intake, and the degree of stress. A discussion of basic concepts of anthropometry precedes examples of advantages and disadvantages of a given anthropometric parameter for selected disease states. The effects of PCM on visceral structure and function are discussed in detail so that the reader can appreciate why the metabolic response to injury may have a very different impact on the nourished compared with the malnourished patient. Particular attention is paid to the adverse effects of PCM on immune function and its antithesis, the beneficial impact of nutritional repletion on the immune system. An approach to refeeding discusses indications for initiation of nutritional support, choice of route, design of a macronutrient and micronutrient regimen, and guidelines for monitoring. Familiarity with the metabolic alterations of refeeding is key to the mitigation of potentially life-threatening complications of sudden refeeding. Appreciation of the anticipated response to nutrition is important, as the response will vary with the degree of stress. A nearly optimal response can be expected with appropriate nutrition in the nonstressed semistarved patient, whereas inefficient repletion is to be expected in the severely stressed patient. The review concludes with a discussion of the role of nutrition as a modifier of the body's metabolic response to injury.

The effect of althesin, ketamine or pentothal on renal function in saline loaded rats

Rats were prepared with chronic cannulae in the carotid artery, jugular vein and urinary bladder; they were then kept 2 days to allow recovery from surgery. A steady-state continuous saline diuresis was established, then various anaesthetic agents were injected and changes in the urine flow, sodium and potassium excretion rates, GFR, ERPF, ERBF and blood pressure were measured. Five groups of rats were studied: (1) control animals given saline in place of any anaesthetic agent, all parameters measured remained constant; (2) althesin (1.2 mg/kg), all parameters remained constant except for the blood pressure which decreased slightly for 5 min; (3) althesin (12 mg/kg); (4) ketamine (50 mg/kg); (5) pentothal (50 mg/kg). The above anaesthetics altered all of the measured parameters except urine output. Various mechanisms for these anaesthetic agents are discussed. In althesin anaesthetized rats, all the retarded renal parameters recovered within 30 min. It is concluded that for the study of renal function, if a brief anaesthesia is needed, althesin is a more suitable anaesthetic agent.

Renal fluoride excretion during and after enflurane anaesthesia: dependency on spontaneous urinary pH-variations

Renal function, fluoride formation and excretion were studied in seven patients during and after enflurane anaesthesia and surgery. The mean maximal plasma level of fluoride was 17.4 microM. It was reached 2 h after termination of anaesthesia. Pre-operatively, fraction fluoride clearance (CF/CIn) was 0.31. During anaesthesia and surgery it decreased to 0.10 and postoperatively rose to 0.55 and 0.77 during two consecutive measurement periods. There was a highly significant correlation (P less than 0.001) between this increase in CF/CIn and the simultaneous rise in urinary pH between the two periods (r = 0.91).

Renal function and fluoride formation and excretion during enflurane anaesthesia

Central circulation, renal function, and fluoride formation and excretion were studied in nine patients during enflurane anaesthesia and surgery. Cardiac output and mean systemic arterial pressure remained unchanged compared with preoperative control values. During anaesthesia and surgery, urine flow rate, inulin clearance, PAH clearance and fractional sodium excretion were 60, 65, 55, and 45% of control values, respectively. Mean peak plasma level of fluoride was 20.0 microM. It was reached 4 hours after termination of anaesthesia. Fluoride clearance (CF) decreased from 23.9 ml . min-1 to 2.7 ml . min-1 during anaesthesia. Postoperative, CF increased to 41.6 and 76.0 ml . min-1, respectively, during two consecutive measurement periods. There was no correlation between plasma fluoride levels and depression of any renal function variable.

Renal function during neurolept anaesthesia

Renal function and central haemodynamics were studied in eight patients, without known histories of renal or cardiovascular disease, during and immediately after upper abdominal surgery under neurolept anaesthesia. Inulin and PAH clearance, fractional sodium and fractional osmolar excretion decreased, while fractional free water reabsorption increased under anaesthesia. Cardiac output, mean systemic arterial pressure and systemic vascular resistance remained virtually unchanged both per- and postoperatively. Renal haemodynamics were promptly restored postoperatively, while fractional sodium and fractional osmolal excretion were unaltered and antidiuresis increased. It is concluded that neurolept anaesthesia, as far as renal function is concerned, is well suited for the anaesthetic management of the poor-risk patient.