Radiocontrast increases plasma and urinary endothelin

Therapeutic potential of endothelin receptor antagonism in kidney disease

Our growing understanding of the role of the endothelin (ET) system in renal physiology and pathophysiology is from emerging studies of renal disease in animal models and humans. ET receptor antagonists reduce blood pressure and proteinuria in chronic kidney disease and cause regression of renal injury in animals. However, the therapeutic potential of ET receptor antagonism has not been fully explored and clinical studies have been largely limited to patients with diabetic nephropathy. There remains a need for more work in nondiabetic chronic kidney disease, end-stage renal disease (patients requiring maintenance dialysis and those with a functioning kidney transplant), ischemia reperfusion injury, and sickle cell disease. The current review summarizes the most recent advances in both preclinical and clinical studies of ET receptor antagonists in the field of kidney disease.

Endothelin and tubulointerstitial renal disease

All components of the endothelin (ET) system are present in renal tubular cells. In this review, we summarize current knowledge about ET and the most common tubular diseases: acute kidney injury (AKI) and polycystic kidney disease. AKI originally was called acute tubular necrosis, pointing to the most prominent morphologic findings. Similarly, cysts in polycystic kidney disease, and especially in autosomal-dominant polycystic kidney disease, are of tubular origin. Preclinical studies have indicated that the ET system and particularly ETA receptors are involved in the pathogenesis of ischemia-reperfusion injury, although these findings have not been translated to clinical studies. The ET system also has been implicated in radiocontrast-dye-induced AKI, however, ET-receptor blockade in a large human study was not successful. The ET system is activated in sepsis models of AKI; the effectiveness of ET blocking agents in preclinical studies is variable depending on the model and the ET-receptor antagonist used. Numerous studies have shown that the ET system plays an important role in the complex pathophysiology associated with cyst formation and disease progression in polycystic kidney disease. However, results from selective targeting of ET-receptor subtypes in animal models of polycystic kidney disease have proved disappointing and do not support clinical trials. These studies have shown that a critical balance between ETA and ETB receptor action is necessary to maintain structure and function in the cystic kidney. In summary, ETs have been implicated in the pathogenesis of several renal tubulointerstitial diseases, however, experimental animal findings have not yet led to use of ET blockers in human beings.

The effects of dexmedetomidine on early stage renal functions in pediatric patients undergoing cardiac angiography using non-ionic contrast media: a double-blind, randomized clinical trial

BACKGROUND

In this study we aimed to investigate the effects of dexmedetomidine on early stage renal function in pediatric patients undergoing cardiac angiography.

METHODS

60 pediatric patients between 6 and 72 months of age undergoing cardiac angiography were included in the study. Patients were divided into two groups. The patients in both groups were administered 1 mg · kg(-1) ketamine, 1 mg · kg(-1) propofol as bolus and followed by 1 mg · kg(-1) · h(-1) ketamine and 50 μg · kg(-1) · min(-1) propofol infusion. Additionally, a loading dose of 1 μg · kg(-1) dexmedetomidine given over 10 min followed by 0.5 μg · kg(-1) · h(-1) dexmedetomidine infusion to patients in group D. The patients were evaluated for NGAL, creatinine, renin, endothelin-1, TAS and TOS blood levels before the procedure and 6th and 24th h after the procedure. pRIFLE criteria were used to define CIN and its incidence in the study.

RESULTS

According to pRIFLE criteria contrast-induced acute kidney injury developed in 3 (10%) of the patients in group D and 11 (36.7%) of the patients in group C (P = 0.029, risk ratio = 0.27; 95% CI: 0.084-0.88). In patients who developed CIN, Endothelin-1 levels in groups C and D were significantly higher than baseline levels at 6th, 24th and 6th h, respectively. Renin levels were significantly increased at 6th and 24 th( ) h in patients with CIN in both groups.

CONCLUSIONS

Dexmedetomidine may be beneficial in protecting against contrast-induced nephropathy during pediatric angiography by preventing the elevation of vasoconstrictor agents such as plasma endothelin-1 and renin.

Direct coronary stenting in reducing radiation and radiocontrast consumption

Introduction

Coronary stenting is the primary means of coronary revascularization. There are two basic techniques of stent implantation: stenting with balloon predilatation of stenosis and stenting without predilatation (direct stenting). Limiting the time that a fluoroscope is activated and by appropriately managing the intensity of the applied radiation, the operator limits radiation in the environment, and this saves the exposure to the patient and all personnel in the room. Nephrotoxicity is one of the most important properties of radiocontrast. The smaller amount of radiocontrast used also provides multiple positive effects, primarily regarding the periprocedural risk for the patients with the reduced renal function. The goal of the study was to compare fluoroscopy time, the amount of radiocontrast, and expenses of material used in direct stenting and in stenting with predilatation.

Patients and methods

In a prospective study, 70 patients with coronary disease were randomized to direct stenting, or stenting with predilatation.

Results

Fluoroscopy time and radiocontrast use were significantly reduced in the directly stented patients in comparison to the patients stented with balloon-predilatation. The study showed a significant reduction of expenses when using a direct stenting method in comparison to stenting with predilatation.

Conslusions

If the operator predicts that the procedure can be performed using direct stenting, he is encouraged to do so. Direct stenting is recommended for all percutaneous coronary interventions when appropriate conditions have been met. If direct stenting has been unsuccessful, the procedure can be converted to predilatation.

ASDIN Original Investigations: Venous Mapping Using Venography and the Risk of Radiocontrast-Induced Nephropathy

Venous mapping using venography has been considered to be the gold standard for identifying veins suitable for arteriovenous fistula (AVF) creation. By utilizing a radiocontrast medium, however, venography introduces the risk of radiocontrast-induced nephropathy. The risk of this complication in the chronic kidney disease (CKD) population has not been previously studied. Twenty-five consecutive patients (CKD stage 4 and 5) undergoing venography were enrolled in this study. Patients were advised not to fast for the procedure and were encouraged to take oral fluids. Radiocontrast-induced nephropathy was defined as a 20% decrease in the estimated glomerular filtration rate (GFR) from the baseline value at 48 hours after contrast administration. Weekly telephone calls were made for a total of 4 weeks to assess the need for dialysis. Venography was performed by interventional nephrology using 10-20 cc of low osmolarity contrast medium. Data were collected prospectively. Median age was 48.9 +/- 7.8 years and 52% of the patients had diabetes. Complete sets of pre- and postprocedure GFRs were available in 21 patients. At 48 hours, there were no differences between the pre- and postprocedure GFRs. At the third week, one patient developed flu-like symptoms with severe gastroenteritis and was hospitalized for volume depletion. This patient initiated dialysis during the hospital stay. We conclude that at 48 hours, our cohort did not develop radiocontrast-induced nephropathy. During the 4-week phone call follow-up, only one patient needed dialysis. Large-scale studies with a longer follow-up using GFR estimation are needed to confirm these preliminary findings.

Clinical and Experimental Evidence for Prevention of Acute Renal Failure Induced by Radiographic Contrast Media

Acute renal failure still occurs as a complication after radiographic examination using iodinated radiocontrast medium. The incidence rate of radiocontrast medium-induced nephropathy (radiocontrast nephropathy) is low (2 - 3%) in general. However, the rate is remarkably elevated in patients with pre-existing renal insufficiency. Radiocontrast nephropathy is associated with increased morbidity and mortality, particularly in patients with percutaneous coronary interventions. Although the reduction in renal blood flow and direct toxic action on renal tubular cells are considered to be involved, little is known about the etiology of radiocontrast nephropathy. A number of agents that improve renal circulation have been clinically tested for prevention of radiocontrast nephropathy, but none of them has succeeded. Protection of renal tubular cells against oxidative stress is another approach to avoid radiocontrast nephropathy. Prophylactic effects of antioxidants such as N-acetylcysteine and ascorbic acid have been reported by several investigators, although the effectiveness of these compounds is still a matter of debate. At present, hydration is regarded as the only effective, though incomplete, prophylactic regimen for radiocontrast nephropathy. Recently, we have shown that caspase-dependent apoptosis is an important factor in the pathogenesis of radiocontrast nephropathy and clarified cellular mechanisms underlying the radiocontrast media-induced apoptosis. This review summarizes clinical and experimental evidence for the etiology and prevention of radiocontrast nephropathy.

Novel approaches to the treatment of acute renal failure

Acute renal failure (ARF) occurs frequently in hospitalised patients and is associated with significant morbidity and mortality. Many therapeutic strategies have been undertaken both to prevent acute renal injury and, once ARF occurs, to improve renal function and reduce mortality. Among the available pharmacological options, no specific therapy has been shown to alter the course of ARF. This article reviews the efficacy of several strategies in experimental renal disease and raises the possibility that similar interventions might be available to the clinician in the near future for the prevention and management of ARF. The prospect of these novel strategies, together with the ever-increasing understanding of the complex pathophysiology of ARF, offers the promise of effective and more physiological therapeutic interventions in this new millennium.

Contrast nephropathy : an evidence-based approach to prevention

Contrast-induced nephropathy occurs in 2-10% of patients exposed to intravascular radiographic contrast agents and results in significant morbidity and mortality. Although the exact mechanism of this disorder has not been fully elucidated, contrast nephropathy is probably due to a combination of decreased renal medullary blood flow, resulting in medullary ischemia, and direct toxicity to renal tubules. Contrast nephropathy is most commonly defined as either a >25% increase or a >0.5 mg/dL rise in serum creatinine level within 48 hours of contrast medium exposure. Baseline characteristics associated with an increased risk for development of contrast nephropathy include the presence of baseline renal dysfunction, diabetes mellitus, congestive heart failure, volume depletion, and concomitant administration of nephrotoxic drugs. Many strategies have been investigated in an effort to prevent the occurrence of renal dysfunction following contrast media exposure. Intravenous hydration has been shown to significantly decrease the incidence of nephropathy in high-risk patients. However, trials of several prophylactic pharmacologic interventions have been mostly disappointing, including the administration of calcium channel antagonists, diuretics, dopamine, endothelin receptor antagonists and fenoldopam. The use of N-acetylcysteine has been shown in some trials to decrease the incidence of contrast nephropathy in patients with a baseline renal dysfunction, and should currently be strongly considered in this high-risk patient subgroup in addition to hydration. Our purpose is to review the contemporary literature regarding contrast-induced renal dysfunction and present an evidence-based approach for prevention of this complication.

Role of N-acetylcysteine in the prevention of radiocontrast-induced nephropathy

OBJECTIVE

To examine the role of N-acetylcysteine (NAC) in the prevention of radiocontrast-induced nephropathy (RIN).

DATA SOURCES

A literature search of MEDLINE (1966-December 2001) was performed using the following search terms: N-acetylcysteine, nephropathy, acute renal failure, and radiocontrast.

STUDY SELECTION

Pertinent English-language animal and human studies were reviewed.

DATA SYNTHESIS

Few small animal trials have demonstrated that NAC significantly prevents the development or reduces the severity of acute renal failure. Two human studies demonstrated NAC significantly reduces the occurrence of RIN.

CONCLUSIONS

NAC may reduce the occurrence of RIN in high-risk patients. Further large-scale studies are needed to corroborate findings from earlier trials.

Changes in endothelial, leucocyte and platelet markers following contrast medium injection during angiography in patients with peripheral artery disease

Peripheral artery angiography, a common diagnostic procedure, may cause early and late adverse reactions, such as anaphylaxis, thrombosis and possible progression of the underlying arterial disease. To test the hypothesis that radiographic contrast medium may contribute to these events by adversely affecting the endothelium, leucocytes and/or platelets, 19 subjects undergoing angiography for the investigation and/or treatment of lower limb atherosclerosis were recruited. Blood was obtained from the external iliac vein before, and at serial intervals after, the injection of radiographic contrast medium into the ipsilateral femoral artery for diagnostic use. Markers of endothelial cell injury (von Willebrand factor (vWf)), platelet activation (soluble P-selectin) and leucocyte activation (neutrophil elastase and soluble L-selectin) were measured in citrated plasma. Soluble intercellular adhesion molecule-1 (sICAM-1) and thromboxane B(2), which are non-specific markers of inflammation, were also measured. Compared with the sample prior to angiography, levels of soluble L-selectin and sICAM-1 were reduced (p<0.02) immediately after passage of the last bolus of contrast medium. 15 min later, levels returned to normal but the level of vWf had increased (p<0.02). After 30 min, only levels of thromboxane B(2) were increased (p<0.05). The following day both vWf (p<0.01) and soluble P-selectin (p<0.05) were increased. These data point to both early and late effects of contrast medium on markers of endothelial, platelet and leucocyte function.

Endothelin: what does the radiologist need to know?

Endothelin (ET) is a potent endogenous vasoconstrictor peptide. It has been implicated in various pathological states since its discovery in 1988. The cardiovascular system and the kidneys are important sites for the action of this peptide. Two types of ET receptor, ETA and ETB, govern the biological effects of ET. Drugs that can prevent the endogenous synthesis of ET or block its binding to receptors may offer important therapeutic impact to patients with congestive heart failure, pulmonary hypertension and acute renal failure. Areas of particular interest to the radiologist include the role of ET in mediating some of the side effects of contrast media, particularly contrast medium nephropathy, and the involvement of ET in the pathogenesis of restenosis following angioplasty. This review outlines the basic biology of this important mediator and its role in health and disease.

Novel approaches to the treatment of acute renal failure

Acute renal failure (ARF) occurs frequently in hospitalised patients and is associated with significant morbidity and mortality. Many therapeutic strategies have been undertaken both to prevent acute renal injury and, once ARF occurs, to improve renal function and reduce mortality. Among the available pharmacological options, no specific therapy has been shown to alter the course of ARF. This article reviews the efficacy of several strategies in experimental renal disease and raises the possibility that similar interventions might be available to the clinician in the near future for the prevention and management of ARF. The prospect of these novel strategies together with the ever-increasing understanding of the complex pathophysiology of ARF, offers the promise of effective and more physiological therapeutic interventions in this new millennium.

The renoprotective potential of endothelin receptor antagonists

The endothelin system has been identified as having a substantial role in renal failure, both acute and chronic. Beside its well characterised haemodynamic effects, its mitogenic and pro-fibrotic properties have gained increased interest in the pathophysiology of chronic renal failure. This review outlines the role of endothelin in the pathogenesis of various renal diseases with a special focus on the potential of blocking this system with endothelin receptor antagonists. So far, most data were derived from animal models, but they provide strong evidence that endothelin receptor antagonists may represent a powerful therapeutic strategy in ameliorating the course of acute and chronic renal failure.

Exacerbation of radiocontrast nephrotoxicity by endothelin receptor antagonism

BACKGROUND

Endothelin is a potent vasoconstrictor that has been implicated in the pathogenesis of radiocontrast nephrotoxicity. Endothelin antagonists may reduce the renal hemodynamic abnormalities following radiocontrast administration.

METHODS

One hundred fifty-eight patients with chronic renal insufficiency [mean serum creatinine +/- SD = 2.7 +/- 1.0 mg/dL (242. 3 to +/- 92.8 micromol/L)] and undergoing cardiac angiography were randomized to receive either a mixed endothelin A and B receptor antagonist, SB 290670, or placebo. All patients received intravenous hydration with 0.45% saline before and after radiocontrast administration. Serum creatinine concentrations were measured at baseline, 24 hours, 48 hours, and 3 to 5 days after radiocontrast administration. The primary end point was the mean change in serum creatinine concentration from baseline at 48 hours; the secondary end point was the incidence of radiocontrast nephrotoxicity, defined as an increase in serum creatinine of > or =0.5 mg/dL (44 micromol/L) or > or = 25% from baseline within 48 hours of radiocontrast administration.

RESULTS

The mean increase in serum creatinine 48 hours after angiography was higher in the SB 209670 group [0.7 +/- 0. 7 mg/dL (63.5 +/- 58.6 micromol/L)] than in the placebo group [0.4 +/- 0.6 mg/dL (33.6 +/- 55.1 micromol/L), P = 0.002]. The incidence of radiocontrast nephrotoxicity was also higher in the SB 209670 group (56%) compared with placebo (29%, P = 0.002). This negative effect of SB 209670 was apparent in both diabetic and nondiabetic patients. Adverse effects, especially hypotension or decreased blood pressure, were more common in the SB 209670 group.

CONCLUSIONS

In patients with chronic renal insufficiency who were undergoing cardiac angiography, endothelin receptor antagonism with SB 209670 and intravenous hydration exacerbate radiocontrast nephrotoxicity compared with hydration alone.

Contrast medium- and mannitol-induced apoptosis in heart and kidney of SHR rats

The induction of apoptosis by contrast media (CM) and mannitol (M) was investigated in the hearts and kidneys of 12-mo-old male SHR rats. Ten groups of 3 SHR rats received a dose of 5 ml/kg of one of the following: Hypaque (H)-30, H-60, H-76, Omnipaque (O)-140, O-350, mannitol (M)-4%, M-9%, M-19%, M-27%, or saline (S). DNA fragmentation was detected using the terminal deoxynucleotidyl transferase-mediated [TdT] dUTP nick-end labeling (TUNEL) method, and the morphology characteristics of apoptosis were confirmed in cardiac and renal cells. The immunoreactivities of Bcl-2, Bax, and p53 were assessed immunohistochemically in the kidneys. Apoptosis occurred in cardiac myocytes and renal tubular and glomerular cells as well as in vascular endothelial and smooth muscle cells of the heart and kidneys. The high frequency of apoptosis correlated significantly with the increase in the osmolality of the H, O, and M. The increased Bax, the increased p53, and the decreased Bcl-2 immunoreactivities were detected in H- or O-treated, but not in M-treated, rats. These findings suggest that CM and M activate cardiac and renal apoptosis by different mechanisms and that the apoptotic process may be implicated in acute heart and renal damage.

The haemodynamic effects of iodinated water soluble radiographic contrast media: a review

All classes of iodinated water-soluble radiographic contrast media (RCM) are vasoactive with the iso-osmolar dimers inducing the least changes in the vascular tone. The mechanisms responsible for RCM-induced changes in the vascular tone are not fully understood and could be multifactorial. A direct effect on the vascular smooth muscle cells causing alterations in the ion exchanges across the cell membrane is thought to be an important factor in RCM-induced vasodilatation. The release of the endogenous vasoactive mediators adenosine and endothelin may also play a crucial role in the haemodynamic effects of RCM particularly in the kidney. In addition, the effects of RCM on blood rheology can cause a reduction in the blood flow in the microcirculation. The purpose of this review is to discuss the pathophysiology of the haemodynamic effects of RCM and to offer some insight into the biology of the endothelium and vascular smooth muscle cells as well as the pharmacology of the important vasoactive mediators endothelin and adenosine.

Urinary endothelin in adolescents and young adults with insulin-dependent diabetes mellitus: relation to urinary albumin, blood pressure, and other factors

Endothelin (ET) is a potent vasoconstrictive peptide that may play a role in vascular pathology in general and diabetic nephropathy in particular. The aim of this study was to investigate (1) alterations of urinary ET1 (UET1) in adolescents and young adults with insulin-dependent diabetes mellitus (IDDM) and (2) the relation of UET1 to other indices of diabetic nephropathy and to risk factors of diabetic angiopathy in general. In 130 IDDM subjects aged 15.2+/-4.9 years with a diabetes duration of 7.3+/-5.1 years, UET1 by radioimmunoassay, urinary albumin by nephelometry, plasma renin by immunoradiometric assay, hemoglobin A1c (HbA1c) by high-performance liquid chromatography, and routine biochemistry analyses were determined. Forty-eight controls, healthy siblings of the diabetics of comparable age, were similarly studied. Total 24-hour UET1 excretion was higher in diabetics than in controls (10,866+/-7,270 and 6,598+/-3,294 pg/24 h, respectively, P=.000). This difference was also noted if male and female diabetics were separately compared with controls. In diabetics with normoalbuminuria (<20 microg/min), total 24-hour UET1 excretion was also higher than in controls (P=.002). In diabetics but not in controls, 24-hour UET1 values were higher in males than in females (P=.018). In IDDM subjects, UET1 showed a linear relationship with age (P=.002), urinary albumin (P=.000), serum creatinine (P=.001), systolic blood pressure (P=.038), triglycerides (P=.003), and HbA1c (P=.041). Multiple regression analysis demonstrated that the variables interacting independently with UET1 were urinary albumin (P=.003) and serum creatinine (P=.038). UET1 is elevated early (in adolescence) in IDDM subjects, and it is positively correlated with the degree of albuminuria. These data suggest that the amount of UET1 possibly reflects the severity of diabetic renovascular damage. It may thus be speculated that UET1 could be used as another index of diabetic nephropathy or its progress.

Influence of contrast media on the response of rat renal arteries to endothelin and nitric oxide: influence of contrast media

RATIONALE AND OBJECTIVES

Contrast media (CM) such as diatrizoate meglumine (DTZ) or iohexol can cause renal vasoconstriction in vivo, and this may initiate CM-induced nephropathy. Endothelin-1 (ET-1), a vasoconstrictor, and nitric oxide, a vasodilator, are key modulators of renal circulation. We tested the hypothesis that CM enhances arterial responses to ET-1, or diminishes responses to nitric oxide.

METHODS

A video dimension analyzer continuously recorded changes in diameter of isolated, pressurized rat interlobar renal arteries (200-400 microm diameter) superfused with combinations of CM, ET-1, nitric oxide, and other vasoactive agents.

RESULTS

Superfusion of arteries with 3.3% DTZ, but not with 3.3% iohexol, enhanced their sensitivity to ET-1 by approximately twofold, as assessed by shifts in concentration-response curves. Both DTZ and iohexol decreased the sensitivity of arteries to nitric oxide by approximately threefold. Neither DTZ nor iohexol affected arterial sensitivity to other vasoconstrictors (phenylephrine, potassium) or vasodilators (forskolin, diltiazem).

CONCLUSIONS

Diatrizoate meglumine and iohexol may induce or augment renal vasoconstriction in part by causing selective alterations in arterial sensitivity to ET-1 and to nitric oxide.

Hypercholesterolemia aggravates radiocontrast nephrotoxicity: protective role of L-arginine

It is well known that the radiocontrast-induced ARF depends on risk factors often associated with compromised renal circulation. Since studies have shown that endothelium-dependent vasodilation is impaired in hypercholesterolemia (HC), we studied the effect of radiocontrast (RC) administration (6 ml/kg body wt, via femoral artery) in salt-depleted rats that were kept on a normal cholesterol (NC) or HC diet (4% cholesterol and 1% cholic acid). Inulin clearance (CIn, ml/min/100 g body wt), renal blood flow (RBF; electromagnetic flowmeter, ml/min/100 g body wt), and fractional excretions of sodium, potassium and water (FENa, FEK and FEH2O, respectively), cholesterol (mg/dl), and albumin (g/dl) were measured 24 hours after radiocontrast administration. The administration of RC to HC rats (RCHC) resulted in lower values of CIn compared with NC rats (RCNC) and control rats: 0.36 +/- 0.085 versus 0.76 +/- 0.13 (RCNC; P < 0.01), versus 0.84 +/- 0.03 (control HC; P < 0.01), versus 0.87 +/- 0.06 (control NC; P < 0.01). Hypercholesterolemia per se did not alter renal function, and control HC versus control NC was not significant. Renal blood flow was significantly lower in the RCHC when compared to RCNC (4.3 +/- 0.3 vs. 6.1 +/- 0.3; P < 0.001) and to control animals (control HC 8.2 +/- 0.3; P < 0.001), and control NC 7.5 +/- 0.33 (P < 0.001). To study the role of nitric oxide (NO), HC rats were treated with an infusion of L-arginine or D-arginine (150 mg via femoral artery) in a 50 mg bolus before RC administration and the remaining dose continuously for a period of one hour. The administration of L-arginine to RCHC rats resulted in significantly higher CIn (0.86 +/- 0.1; P < 0.001) when compared to the untreated rats (RCHC). D-arginine did not show a significant difference in CIn (0.49 +/- 0.08). There was a considerable difference between D-arginine RCHC and L-arginine RCHC (P < 0.05). The RBF fall was prevented by L-arginine in RCHC (8.4 +/- 0.23 vs. 4.3 +/- 0.3; P < 0.001), but it was not prevented by D-arginine (5.1 +/- 0.57; P < 0.001). Our data suggest that hypercholesterolemia aggravates nephrotoxicity, which is attenuated by L-arginine but not by D-arginine administration, suggesting that nitric oxide plays a significant role in this model of acute renal failure.

Contrast media-induced nephrotoxicity--questions and answers

The intravascular administration of contrast media (CM) can produce acute haemodynamic changes in the kidney characterized by an increase in renal vascular resistance and a decrease in the glomerular filtration rate (GFR). These changes may lead to clinically significant reduction in renal function in patients with pre-existing risk factors such as diabetic nephropathy, congestive heart failure and dehydration. The pathophysiology of the renal haemodynamic effects of CM involves activation of the tubuloglomerular feedback (TGF) mechanism and the modulation of the intrarenal production of vasoactive mediators such as prostaglandins, nitric oxide, endothelin and adenosine. The TGF response is osmolality-dependent and accounts for about 50% of the acute functional effects of high osmolar CM on the kidney. Reduction in the synthesis of the endogenous vasodilators nitric oxide and prostaglandins increases the nephrotoxicity of CM. Endothelin and adenosine play a crucial role in mediating the acute functional effects of CM. Antagonists of these mediators attenuate the reduction in renal function induced by contrast agents. Vacuolization of the cells of the proximal tubules and necrosis of those of the medullary ascending limbs of loops of Henle are the main structural effects of CM in the kidney. The reduction in renal function induced by CM could be minimized by the use of low osmolar CM and adequate hydration. The prophylactic administration of calcium channel blockers and adenosine antagonists such as theophylline may also offer some protective effect.

Beneficial effect of ETA receptor blockade in a rat model of radiocontrast-induced nephropathy

Endothelin has been implicated in the pathogenesis of acute renal failure associated with radiocontrast media. The current study was designed to determine the effect of endothelin receptor blockade in a model of radiocontrast-induced nephropathy. Inhibition of prostanoids and nitric oxide with indomethacin and L-nitroarginine methyl ester (L-NAME) predisposes rats to the nephrotoxic effects of radiocontrast media and, therefore, has been proposed as a clinically relevant model. Separate groups of conscious rats were given the ETA receptor antagonist, A-127722 (3, 10, or 30 mg/kg), or water (1 mL/kg) by oral gavage. All rats were then given indomethacin (10 mg/kg), L-NAME (10 mg/kg), and the contrast agent, diatrizoate (6 mL/kg), by intravenous injection at 15-min intervals. Urine was collected for the subsequent 24 h by placing rats in metabolism cages. When indomethacin, L-NAME, and diatrizoate were administered without A-127722, rats displayed typical signs of renal failure; protein excretion was increased from a baseline of 13 +/- 2 to 33 +/- 8 mg/day (p < 0.05) and plasma creatinine increased from 0.52 +/- 0.01 to 0.62 +/- 0.04 mg/dL (p < 0.05). ETA receptor blockade prevented the rise in protein excretion and plasma creatinine in a dose-dependent manner. In separate series of clearance experiments, A-127722 completely inhibited the renal effects of exogenous ET-1. These results suggest that endothelin plays a role in the hemodynamic events in this model and that ETA receptor antagonists should be investigated as potential therapeutic agents for radiocontrast-induced nephropathy.

Endothelin and atrial natriuretic peptide levels following radiocontrast exposure in humans

Radiocontrast exposure is associated with vasoconstriction of the renal vascular bed and, in certain circumstances, with acute renal failure. This may be influenced by the volume of contrast infused or underlying disease, such as diabetes or renal failure. Changes in circulating vascular regulators, such as endothelin and atrial natriuretic peptide (ANP), may play a role in the development and/or prevention of acute renal failure. Nineteen patients undergoing arteriographic procedures were divided into two groups: large-volume contrast (> or = 150 mL; n = 7) and small-volume contrast (< 150 mL; n = 12). Circulating endothelin levels increased significantly (from 12.3 +/- 1.1 pmol/L to 19.4 +/- 2.2 pmol/L; P < 0.05) following large-volume contrast exposure (group 1) but not following small-volume contrast exposure (group 2) (13.9 +/- 1.7 pmol/L to 12.2 +/- 0.09 pmol/L). ANP levels increased significantly in both groups: 43 +/- 15 pg/mL to 75 +/- 21 pg/mL in group 1 and 33 +/- 16 to 106 +/- 39 pg/mL in group 2. Data from an additional eight patients with underlying diabetes mellitus and/or renal insufficiency also were obtained and were considered separately. Endothelin levels were higher at baseline and increased significantly after contrast (25.7 +/- 5 pmol/L to 55.4 +/- 18 pmol/L) despite the relatively small average volume of contrast infused (112 +/- 15 mL). ANP levels were also highest in these patients (211 +/- 43 pg/mL precontrast and 323 +/- 65 pg/mL postcontrast). No group had a significant change in serum creatinine following contrast exposure. In conclusion, large-volume radiocontrast exposure is associated with an increase in both circulating endothelin and ANP levels. Patients with underlying diabetes or renal insufficiency may have higher baseline levels and a greater tendency to increase endothelin after contrast exposure. While an increase in endothelin may contribute to renal vasoconstriction following radiocontrast exposure, simultaneous increases in ANP may serve to offset this response and protect against changes in renal function.

Role of endothelium-derived nitric oxide-endothelin balance in contrast medium-induced acute renal vasoconstriction in dogs

RATIONALE AND OBJECTIVES

The authors evaluated the involvement of nitric oxide and endothelin in radiographic contrast medium-induced changes in renal hemodynamics.

METHODS

Eleven anesthetized healthy dogs were each studied during three periods. Thirty minutes before the first, second, and third periods, the dogs received 1 mL per kilogram of body weight of isotonic saline, L-N-nitro-L-arginine-methyl-ester (L-Name, 10 mg/kg intravenously), and L-arginine (500 mg/ kg intravenously), respectively. Renal blood flow (RBF) and mean arterial blood pressure were continuously monitored. The glomerular filtration rate (GFR) was evaluated by means of polyfructosan clearance.

RESULTS

Contrast medium induced a significant (P < .05) decrease in RBF and GFR and a significant (P < .05) increase in urinary endothelin excretion. L-Name enhanced the effect of contrast media on RBF and GFR. L-arginine attenuated the effect of L-Name on the contrast medium-induced reduction of GFR.

CONCLUSION

These findings support the hypothesis that acute contrast medium-induced intrarenal vasoconstriction may involve an imbalance of endothelial vasoactive agents, nitric oxide, and endothelin, and they confirm the involvement of hemodynamic changes in contrast medium-induced nephropathy.

Distribution of endothelin immunoreactivity in human kidney correlates with antemortem acute renal failure: a possible postmortem immunohistochemical test

The role of endothelin in the normal kidney function, as well as in disease states, has been studied in animal models. In addition, it was shown previously that endothelial, mesangial, and epithelial components of the nephron produce endothelins, in particular ET-1. We performed immunohistochemistry for ET-1 reactivity on 31 autopsy and four surgically removed kidneys. Eighteen cases had clinical diagnoses of acute renal failure (ARF) In the remaining 17 cases with normal or unchanged renal function before death or surgery, ET-1 immunoreactivity was present in tubular epithelium, with the most intense staining in the medullary collecting tubules. In 13 of 18 cases of ARF, tubular staining was either replaced or accompanied by interstitial reactivity in the inner and outer medulla, corresponding to the location of the vasa recta and interlobular arteries identified by factor VIII immunostaining. Controlled autolysis performed on normal kidney over 72 hours postmortem produced tubular epithelial degradation with reduced epithelial cell endothelin reactivity, but not an interstitial pattern. In situ hybridization for ET mRNA localized expression to tubular and collecting duct epithelium in both normal and acute renal failure cases. The change in the localization of ET-1 immunoreactivity from tubular epithelium to the interstitium in these ARF cases does not appear to be the result of increased vascular endothelial production of endothelin. This altered immunoreactivity pattern for ET-1 may be a marker of antemortem tubular damage and can be used as an adjunct in the autopsy diagnosis of ARF.

Protection from the nephrotoxicity of contrast dye

Previous studies have reported a 4%-50% incidence of acute renal failure (ARF) following the use of radiocontrast media in patients with preexisting chronic renal insufficiency. In these studies, ARF was defined as a rise of the serum creatinine of at least 1 mg/dl above baseline. Using the same criteria, we studied 214 patients undergoing various intravascular radiocontrast media procedures. Patients were infused with a specially prepared cocktail solution (NSMF) containing 1000 ml half-normal saline, 12.5 g of mannitol (M), I ampule NaHCO3, and 200 mg of furosemide (F) at 100 ml/h from one hour prior to two hours after the procedure. Urinary output was replaced with normal saline for at least 6 h after the procedure. Seven percent of the patients developed acute renal insufficiency. Only 3% of the patients had a rise in serum creatinine greater than 2 mg/dl. No patient required dialysis therapy after the procedure. There was one unrelated death caused by acute myocardial infarction postangioplasty. Risk factors for development of ARF despite cocktail administration included the presence of diabetes mellitus and angiotensin converting enzyme (ACE) inhibitor therapy. We concluded that the properly administered NSMF solution protects against radiocontrast dye induced renal failure. In select patients with chronic renal insufficiency, consideration should be given to withholding ACE inhibitor therapy for 24-48 h prior to administration of intravenous radiocontrast dye. A large controlled trial will be required to establish whether the NSMF solution offers benefit beyond that of saline hydration alone.

Endothelin receptors in normal and diseased kidneys

1. Endothelin-1 (ET-1), the most potent vasoconstrictor yet identified, mediates a multitude of responses in various tissues including the kidney. The biological responses of ET-1 are mediated by specific cell surface receptors classified as ET(A) and ETB. Species differences are observed in the distribution as well as function of these ET receptors. 2. Involvement of ET has been demonstrated in a number of renal diseases, including ischaemia-induced acute renal failure, chronic renal failure, radiocontrast and cyclosporin-induced nephrotoxicity. ET antibodies as well as ET receptor antagonists have been shown to be beneficial in these disease models.

Role of endothelin in renal function and dysfunction

1. Endothelin has significant effects on renovascular, glomerular and tubular function. 2. Endothelin causes severe renal vasoconstriction, resulting in a decrease in renal blood flow and glomerular filtration rate. 3. Endothelin can inhibit sodium reabsorption and, in the rat, vasopressin-induced water transport. 4. The endothelin receptor subtypes mediating renovascular and tubular effects of endothelin may differ between species. 5. Renal endothelin production, metabolism and receptor binding is altered in a number of renal diseases, including acute and chronic renal failure and cyclosporine and radiocontrast nephrotoxicity. 6. Endothelin receptor antagonists or antibodies can attenuate the severity or progression of a number of renal diseases.

Relationship between the diuretic effect of radiocontrast media and their ability to increase renal vascular resistance

The relationship between diuresis and natriuresis induced by radiocontrast media (RCM) and their renal haemodynamic effects were investigated. The effects of the iso-osmolar iotrolan and the hyperosmolar diatrizoate on the renal vascular resistance (RVR) were studied in the filtering and non-filtering variants of the isolated perfused rat kidney (IPRK) preparation. In the non-filtering model, no tubular regulatory process can be activated. The effect of diatrizoate on the RVR of the filtering IPRK in the presence of fursemide (0.3 mmol l-1) an inhibitor of the tubuloglomerular feedback (TGF) was also investigated. There was no significant difference (p > 0.05) in the response of the filtering (n = 6) and non-filtering (n = 6) IPRK to iotrolan. The induced reduction in the renal perfusate flow (RPF) by iotrolan was 20.5 +/- 3.05% and 22.9 +/- 3.03%, respectively. The reduction in the RPF which was observed with diatrizoate in the non-filtering IPRK (n = 5, 17.5 +/- 3.04%) was significantly less (p < 0.05) in comparison to that of the filtering IPRK (n = 6, 26.9 +/- 4.28%). In the frusemide experiments, a reduction in the RPF comparable to that of the non-filtering kidney was observed (n = 5, 13.7 +/- 4.34%). This study demonstrates that the renal vascular effect of diatrizoate is partially dependent on the TGF response. No tubular regulatory mechanism was accountable for the haemodynamic effect of iotrolan. The activation of the tubular response is osmolarity dependent.

Nitric oxide and prostanoids protect the renal outer medulla from radiocontrast toxicity in the rat

Human radiocontrast nephrotoxicity is predicted by the presence of multiple risk factors, often associated with compromised renal circulation. To produce a simple model of radiocontrast nephropathy, rats were pretreated with indomethacin and N omega-nitro-L-arginine methyl ester (L-NAME, to inhibit nitric oxide synthesis) before the administration of iothalamate. Acute renal failure consistently developed, with a decline in creatinine clearance from 1.05 +/- 0.10 to 0.27 +/- 0.05 ml/min (P < 0.001) associated with selective necrosis of 49 +/- 9% of medullary thick ascending limbs. Hemodynamic studies using laser-Doppler probes revealed that when injected alone, iothalamate increased outer medullary blood flow to 196 +/- 25% of baseline (P < 0.001). Pretreatment by L-NAME or indomethacin both reduced basal medullary blood flow and transformed the medullary vasodilator response to radiocontrast into vasoconstriction, with a prolonged reduction of medullary blood flow to less then half of baseline. Combined administration of indomethacin, L-NAME, and iothalamate lowered medullary blood flow to 12 +/- 4% of baseline. We conclude that prostanoids and nitric oxide have an important protective role in the renal response to radiocontrast material. Reduced synthesis of these vasoactive substances in renal/vascular diseases may predispose patients to radiocontrast nephropathy.

Iodinated contrast media-induced nephropathy: pathophysiology, clinical aspects and prevention

Administration of iodinated contrast media (CM) for radiographic purposes is a preoccupying cause of acute renal failure. This review of the literature deals with what is known about physiopathology, clinical course, risk factors and prevention. Factors involved in the pathophysiology of CM-induced acute renal failure are vasoconstriction, direct tubular cell injury and tubular obstruction by casts. In the case of pre-existing renal hypoperfusion, CM may disturb the complex interaction between factors which modulate renal haemodynamics by increasing vasoconstrictor factors, notably endothelin peptides. The renal medulla, a zone characterized by a high metabolic activity and a low oxygen tension, may be a specific target for CM-induced effects. CM-induced nephropathy (CMN) is essentially observed in patients with one or more associated risk factors (chronic renal failure, dehydration, diabetes mellitus with impaired renal function, multiple myeloma, large CM volume, intra-arterial rather than intravenous route, etc). There is much debate as to whether newer low osmolar CM (LOCM) are better tolerated than conventional high osmolar CM (HOCM). Most of the animal studies clearly demonstrate the advantages of LOCM over HOCM. Clinical literature is far more confusing, although some recent studies and one meta-analysis demonstrate that LOCM are better tolerated in patients with impaired renal function. The low number of comparative clinical trials carried out in high risk patients, wide variability in CMN definitions, limited number of patients enrolled and inadequacy of various selected endpoints may explain difficulties experienced in demonstrating this advantage. Furthermore, while hydration is correctly maintained during clinical trials, this is not always true in clinical practice. Such a discrepancy could lead to underestimation of the potential advantage of LOCM over HOCM. Effective prevention should associate the correct hydration of patients, identification and, when possible, optimal correction of risk factors, avoidance of repeated CM injections within a short period of time and temporary disruption of treatment with other nephrotoxic drugs (non steroidal antiinflammatory drugs, aminoglycosides, etc).

Reduced depression of renal function by iotrolan in the isolated rat kidney

The direct effects of iotrolan, a non-ionic dimer, on renal function were compared to iopromide, a non-ionic monomer and diatrizoate, an ionic monomer using the isolated perfused rat kidney. Kidneys were perfused ex vivo at 100 mmHg in a recirculating perfusion system with an albumin-based perfusate containing angiotensin II. All contrast media were studied at starting concentration of 20 mg Iodine/ml of renal perfusate. Each contrast agent produced a biphasic effect on the glomerular filtration rate (GFR) characterised by a transient increase followed by a sustained fall. However, the sustained fall in GFR induced by iotrolan (-24.7 +/- 2.1%) was significantly smaller than that produced by diatrizoate (-40.6 +/- 3.5%, P < 0.05) but there was no significant difference in comparison to the fall induced by iopromide (-34.2 +/- 3.7%). Each contrast agent produced a sustained decrease in renal perfusate flow (RPF) with iotrolan exerting a significantly smaller response (-21.7 +/- 2.0%) than either diatrizoate (-29.4 +/- 2.6%, P < 0.05) or iopromide (-32.2 +/- 2.9%, P < 0.05). The results indicate that at an equivalent iodine concentration iotrolan produces a smaller reduction of renal function in comparison to either iopromide or diatrizoate.

Role of endothelin and prostaglandins in radiocontrast-induced renal artery constriction

Infusion of radiocontrast agents in vivo results in renal artery constriction and subsequent renal hypoperfusion. To examine the role of endothelin and of prostaglandins in radiocontrast-mediated renal vasoconstriction, rats were treated with an endothelin receptor antagonist, CP170687, and with indomethacin. The dose of CP170687 utilized was sufficient to reverse endothelin1-mediated constriction of isolated aortic rings and of renal blood flow in intact rats. In normal rats there was a transient drop in renal blood flow to 80% of baseline following sodium iothalamate injection, an effect which was not prevented by CP170687. In rats first given indomethacin, the drop in renal blood flow was more pronounced (to 63% of baseline) and was sustained. In this instance, CP170687 fully reversed the sustained decrease of renal perfusion. CP170687 also diminished the rise in systemic blood pressure seen following iothalamate injection. In the absence of indomethacin, iothalamate increased urinary prostaglandin E2 to a maximum of sevenfold above baseline values. In summary, injection of radiocontrast results in an immediate decrease in renal blood flow that is counteracted by an increase in renal prostaglandin formation. When prostaglandin synthesis is inhibited, prolonged endothelin-mediated renal vasoconstriction is observed that is reversed by an endothelin receptor antagonist.

Endothelins in the kidney: physiology and pathophysiology

In summary, ET may be important in the pathogenesis of multiple diseases of the kidney. Alterations in ET-1 production and action may lead to severe vasoconstriction, mesangial cell contraction, glomerular cell proliferation, and enhanced sodium and water retention. It is not surprising, therefore, that intense investigations are under way in an effort to develop specific inhibitors of ET action, including ECE inhibitors and ET receptor blockers. It is likely that with the development of these agents, we will uncover even more diseases in which ET mediates renal dysfunction and in which, hopefully, blockers of ET action will be of therapeutic benefit.