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

Development of silica-encapsulated silver nanoparticles as contrast agents intended for dual-energy mammography

OBJECTIVE

Dual-energy (DE) mammography has recently entered the clinic. Previous theoretical and phantom studies demonstrated that silver provides greater contrast than iodine for this technique. Our objective was to characterize and evaluate in vivo a prototype silver contrast agent ultimately intended for DE mammography.

METHODS

The prototype silver contrast agent was synthesized using a three-step process: synthesis of a silver core, silica encapsulation and PEG coating. The nanoparticles were then injected into mice to determine their accumulation in various organs, blood half-life and dual-energy contrast. All animal procedures were approved by the institutional animal care and use committee.

RESULTS

The final diameter of the nanoparticles was measured to be 102 (±9) nm. The particles were removed from the vascular circulation with a half-life of 15 min, and accumulated in macrophage-rich organs such as the liver, spleen and lymph nodes. Dual-energy subtraction techniques increased the signal difference-to-noise ratio of the particles by as much as a factor of 15.2 compared to the single-energy images. These nanoparticles produced no adverse effects in mice.

CONCLUSION

Silver nanoparticles are an effective contrast agent for dual-energy x-ray imaging. With further design improvements, silver nanoparticles may prove valuable in breast cancer screening and diagnosis.

KEY POINTS

• Silver has potential as a contrast agent for DE mammography. • Silica-coated silver nanoparticles are biocompatible and suited for in vivo use. • Silver nanoparticles produce strong contrast in vivo using DE mammography imaging systems.

Effectiveness of theophylline in preventing contrast-induced nephropathy after coronary angiographic procedures

BACKGROUND

Contrast-induced nephropathy (CIN) is the third most common cause of hospital acquired acute renal failure and is associated with increased morbidity and mortality. The use of theophylline for prevention of CIN has yielded conflicting results. This study aimed at examining the effectiveness of theophylline in prevention of CIN when added to IV hydration and N-acetylcysteine (NAC).

METHODS

Patients with stable serum creatinine and at least moderate risk for CIN according to Mehran's risk score were included in this parallel group, 1:1, single-blind, randomized controlled trial. All patients received IV hydration (1 mL/kg per hour for 24 hours) and NAC (600 mg bid for 2 days). Patients were randomized to placebo (group P) or theophylline (200 mg in 100 mL 0.9% saline, as IV infusion 30 minutes before contrast medium (CM) administration; group T). Patients underwent standard coronary angiography ± angioplasty. Serum creatinine (SCr) was assessed just before and 72 hours after contrast administration and estimated glomerular filtration rate (eGFR) was calculated.

RESULTS

This study included 60 patients with mean SCr 1.44 ± 0.7 mg/dL and eGFR 60.2 ± 29.2 mL/min. Mean SCr among group T was 1.54 ± 0.7 mg/dL with eGFR 58.6 ± 28.6 mL/min, while group P showed mean SCr of 1.34 ± 0.7 mg/dL and eGFR of 61.8 ± 30.1 mL/min. Among group P, 6 (20%) patients developed CIN while none of the patients in group T developed CIN. In comparison to placebo, theophylline significantly decreased SCr (P = 0.0001) and increased eGFR (P = 0.001) at 72 hours. Multivariate regression analysis showed that receiving placebo instead of theophylline, anemia, congestive heart failure, chronic renal impairment, and high-contrast load are all independent predictors for deteriorating renal function after CM administration.

CONCLUSION

Theophylline seems to be an effective prophylaxis against CIN for moderate- and high-risk patients undergoing coronary angiography or angioplasty. It offers additive protection when added to IV hydration and NAC.

Functional renal imaging: new trends in radiology and nuclear medicine

The objective of this work is to compare the characteristics of various techniques for functional renal imaging, with a focus on nuclear medicine and magnetic resonance imaging. Even with low spatial resolution and rather poor signal-to-noise ratio, classical nuclear medicine has the advantage of linearity and good sensitivity. It remains the gold standard technique for renal relative functional assessment. Technetium-99m ((99m)Tc)-labeled diethylenetriamine penta-acetate remains the reference glomerular tracer. Tubular tracers have been improved: (123)I- or (131)I-hippuran, (99m)Tc-MAG3 and, recently, (99m)Tc-nitrilotriacetic acid. However, advancement in molecular imaging has not produced a groundbreaking tracer. Renal magnetic resonance imaging with classical gadolinated tracers probably has potential in this domain but has a lack of linearity and, therefore, its value still needs evaluation. Moreover, the advent of nephrogenic systemic fibrosis has delayed its expansion. Other developments, such as diffusion or blood oxygen level-dependent imaging, may have a role in the future. The other modalities have a limited role in clinical practice for functional renal imaging.

Contrast-Induced Nephropathy

Contrast-induced nephropathy (CIN) is a well-recognized complication of radiographic contrast administration and is the third leading cause of hospital-acquired renal insufficiency. The use of contrast media is increasing, particularly in the area of endovascular therapy. Vascular interventionists need to be aware of strategies to reduce the risk of CIN. Numerous trials, meta-analyses, and expert guidelines for the prevention of CIN have been published between 1966 and 2006, but the majority of studies have been conducted on patients undergoing coronary interventions; few have involved vascular surgical population. The literature suggests that adequate hydration is essential in all patients due to receive contrast. No pharmacological agents have been shown to conclusively reduce the risk. Forced diuresis is harmful, and there is insufficient evidence to support routine use of hemodialysis or hemofiltration. Well conducted studies of other potential prophylactic techniques are needed in vascular populations.

Facts and fallacies concerning the prevention of contrast medium-induced nephropathy

OBJECTIVE

The aim of this article is to extract from recent medical literature and nephrologic practice the facts and fallacies concerning the possible prophylaxis of contrast medium-induced nephropathy.

DATA SOURCES, STUDY SELECTION, AND DATA EXTRACTION

A MEDLINE/PubMed search (1985 to January 2006) was conducted, including all relevant articles investigating the pathogenesis and prevention of contrast medium-induced nephropathy from a nephrologic critical point of view.

DATA SYNTHESIS

Considerable efforts have been made to develop pharmacologic therapy for the prevention of contrast medium-induced nephropathy, especially in patients at risk, such as elderly subjects and those with preexisting renal impairment, hypovolemia, or dehydration. There is general consensus that hydration protocols implemented before and after imaging with contrast medium may be effective in preventing contrast medium-induced nephropathy. However, definitive and convincing data related to amounts to be infused, infusion timing, and type of solutions (half-isotonic, isotonic saline solution, or bicarbonate) are lacking. Forced diuresis with furosemide or mannitol and use of dopamine, together with concomitant hydration, have been proved to be ineffective or even more risky in the event of inadequate maintenance of euvolemia. Various direct or indirect vasodilators have been investigated (atrial natriuretic peptide, calcium channel blockers, angiotensin-converting enzyme inhibitors, and endothelin receptor antagonists), yet results have been inconsistent and inconclusive. Recent large meta-analyses concerning the protective role of antioxidant action of N-acetylcysteine have led to the conclusion that the statistical significance of the results is borderline. Preventive hemodialysis has not proved to be useful; on the contrary, it might worsen the clinical conditions by inducing hypotension. Hemofiltration, despite some positive studies, is too complex and cannot be used extensively.

CONCLUSIONS

: It is believed that prevention is actually achieved by correcting hypovolemia, dehydration, or both. Normalization of body fluids is probably the true objective to be achieved by preventive measures in all patients, not only in those at risk. Because limited data have been collected in intensive care units, at present, no firm or specific recommendations can yet be provided for the critically ill.

Prophylaxis of Iodinated Contrast Media-Induced Nephropathy

Iodinated contrast media are a frequent cause of acute renal failure, especially in patients whose renal function is already impaired. In addition to hydration, which remains the most commonly acknowledged means of protection, numerous pharmacological approaches for the prophylaxis of contrast nephropathy have been tested so far. They include diuretics, calcium channel blockers, adenosine receptor antagonists, N-acetylcysteine, low-dose dopamine and the dopamine D1 receptor agonist fenoldopam, endothelin receptor antagonists, and even captopril. The present review of the literature critically discusses the drugs used to prevent contrast nephropathy from a pharmacological point of view.

Comparison of computed tomographic angiography with digital subtraction angiography in the diagnosis of cerebral aneurysms: a meta-analysis

OBJECTIVE

To compare a novel diagnostic radiological technique, computed tomographic angiography (CTA), with the standard method, namely digital subtraction angiography (DSA), in the diagnosis of cerebral aneurysms.

METHODS

A comprehensive search of the world literature on CTA was performed. Articles that reported on prospective comparisons of CTA and DSA in the evaluation of patients suspected of harboring cerebral aneurysms were selected for data extraction. Suitable statistical methods were applied to the extracted data for meta-analysis.

RESULTS

Twenty-one references met the criteria for use in the meta-analysis. Unweighted calculations based on data for 1251 patients resulted in a sensitivity of 0.933 (93.3%; range, 75.4-100%) and a specificity of 0.878 (87.8%; range, 0-100%). When the studies were weighted for the number of patients in each study, the sensitivity decreased slightly, to 0.927 (92.7%), and the specificity decreased more substantially, to 0.772 (77.2%).

CONCLUSION

On the basis of this meta-analysis, DSA remains the standard method. However, many who use CTA have reported it to be as good as or better than DSA in the diagnosis and treatment of cerebral aneurysms, as well as being of less risk and discomfort to their patients and easier and less expensive to perform.

Acute renal failure in the PACU

Acute renal failure (ARF) in the PACU can lead to serious morbidity or even death. The incidence of acute renal failure appears to be increasing. This review article is intended to provide the staff in the PACU with relatively easy means to recognize the development of ARF, and provide recommendations for prompt and intensive management. Existence of renal dysfunction, complex surgical procedures that require cardiopulmonary bypass, and vascular surgery involving the aorta are associated with a high incidence of ARF. In spite of the improved overall care of the patient in the PACU, the occurrence of ARF is associated with a very high likelihood of morbidity and mortality. Prompt recognition of the ARF and aggressive management in the PACU may improve the patient's chances of survival. Large-scale, prospective, randomized clinical trials in the PACU setting are needed to determine the most effective management plan. This is a U.S. government work. There are no restrictions on its use.

Contrast agents in patients on dialysis

Contrast media are used to enhance the structural and functional information that is provided by imaging methods. They are used particularly in conventional radiographic (X-ray) investigations, but are also used in magnetic resonance imaging (MRI) and increasingly in ultrasound (US). The water-soluble, iodinated, intravascular radiographic agents are commonly used, and in large doses. They are excreted almost exclusively by the kidney and may have nephrotoxic effects. The use of these agents in patients with renal impairment may potentially be problematic. In this article the chemical composition and pharmacokinetics of these contrast agents are reviewed, as are their potentially toxic effects on the heart, neural tissues, kidney, and endothelium. Their safety for use in the patient with end-stage renal disease (ESRD) and those on dialysis is discussed. This aspect is also addressed briefly for the contrast agents used to augment MRI and US.

Preclinical profile of the monodisperse iodinated macromolecular blood pool agent P743

RATIONALE AND OBJECTIVES

To summarize the chemical synthesis, physicochemical characterization, pharmacokinetic behavior, and biological evaluation of P743, a new macromolecular iodinated contrast medium.

METHODS

The synthesis and molecular modeling of the iodinated macromolecule P743 are described. The pharmacokinetic profile was established in rabbits and rats. Acute toxicity in mice, renal tolerance in normal rabbits, and renal tolerance in uninephrectomized, dehydrated rats undergoing selective intrarenal injection was evaluated. In vitro permeability effects on isolated mastocytes and on the coagulation pathways were carried out. Computed tomography vascular imaging was performed after intravenous injection of P743 (300 mg I/kg) in rabbits and compared with the nonspecific nonionic agent iobitridol.

RESULTS

P743 is a monodisperse, macromolecular iodinated contrast medium. In both rabbits and rats, P743 showed a pharmacokinetic profile consistent with that of a rapid-clearance blood-pool agent. Its diffusion through the endothelium was found to be low in vitro, thus confirming early confinement of this macromolecule, unlike nonspecific contrast media. In both species, P743 was excreted by glomerular filtration. Acute toxicity disclosed no mortality at the highest volume that could be injected into mice, leading to a median lethal dose greater than 8.9 g I/kg. Renal tolerance was found to be good in both euvolemic rabbits and uninephrectomized, dehydrated rats. No histamine or leukotriene B4 release was found on RBL-2H3 isolated mastocytes. P743 did not interfere with the coagulation pathways. Imaging experiments confirmed that P743 remains in the vascular compartment for a longer time than does iobitridol, thus allowing vascular enhancement that is twice as high as that of iobitridol in the recirculation phase.

CONCLUSIONS

The pharmacokinetic and imaging profiles of P743, a new, monodisperse, macromolecular blood-pool iodinated contrast medium, were consistent with those of a rapid-clearance blood-pool agent. Its initial safety profile is satisfactory. Further experimental imaging studies are required to define the clinical interest in such molecules.

Hemodynamic effect of iodinated high-viscosity contrast medium in the rat kidney: a diffusion-weighted MRI feasibility study

RATIONALE AND OBJECTIVES

To assess the abilities of dynamic diffusion-weighted MRI to demonstrate the effects in vivo of a high-viscosity iodinated contrast agent on medullary and cortical blood flow in the rat kidney.

METHODS

Dynamic diffusion-weighted, echoplanar MR images obtained from five b-value single-shot acquisitions and their isotropic apparent diffusion coefficient maps were obtained from nine rats anesthetized by pentobarbital sedation, before and after intravenous injection of a high-viscosity, dimeric iso-osmolar iodinated contrast medium (iodixanol), and compared with those obtained from four control rats that received saline.

RESULTS

The mean baseline apparent diffusion coefficient values were 1.64 +/- 0.05 x 10(-3) mm2/s for the cortex and 1.75 +/- 0.06 x 10(-3) mm2/s for the medulla. In the iodixanol group, a significant decrease in renal diffusion was observed at 12 minutes and lasted at least until 24 minutes. The decrease in diffusion occurred earlier for the cortex and lasted less than for the medulla. There was no significant modification in diffusion over time in the control group.

CONCLUSIONS

This preliminary experience in rats shows that dynamic diffusion-weighted MRI can be used to study noninvasively the in vivo renal hemodynamic response after injection of iodinated contrast.

Reversibility of experimental acute renal failure in rats: assessment with USPIO-enhanced MR imaging

The purpose of this study was to evaluate the potential reversibility of kidney lesions in an experimental model of acute renal failure using ultra-small particles of iron oxide (USPIO)-enhanced magnetic resonance (MR) imaging. This study was conducted in 21 uninephrectomized rats using a model of iodinated contrast media-induced renal failure. Thirteen rats received selective intraarterial renal administration of diatrizoate (370 mg/ml) and were compared with two control groups, including six animals injected with saline and two noninjected animals. MR imaging was performed 28 hours, 8 days, and 22 days after the procedure. Each MR session included axial and coronal T1- and coronal T2-weighted images before and after intravenous administration of 60 micromol Fe/kg of USPIO. The rats were sacrificed immediately after the last MR session for pathologic evaluation. MR images were qualitatively and quantitatively interpreted with respect to pathologic data, and differences were statistically studied. At day 22, histology showed 4 severely diseased kidneys with focal areas of necrosis, 5 mildly diseased kidneys with tubular vacuolization, and 12 normal kidneys. On quantitative data, a high correlation between the percentage of negative enhancement and histologic data was observed (P < 0.05). Qualitative interpretation showed a sensitivity and specificity of USPIO-enhanced T2-weighted MR images of 88% and 91%, respectively. Follow-up enhancement curves showed a constant increase of intrarenal USPIO negative enhancement in normal kidneys between day 1 and day 22, whereas all severely involved kidneys displayed higher USPIO negative enhancement at day 1 without significant changes over time until day 22. USPIO may be useful for in vivo follow-up of the reversibility of experimentally induced iodinated contrast media renal impairment in animals.

A comparison of the efficacy and safety of ioxaglate and iobitridol in renal angioplasty

PURPOSE

To compare ioxaglate and iobitridol for percutaneous transluminal renal angioplasty (PTRA) as regards thromboembolic complications, the quality of diagnosis, and renal and general safety.

METHODS

One hundred and eighty-nine patients were prospectively studied, 98 of whom received ioxaglate, and 91, iobitridol. Twenty-two were secondarily excluded from the evaluation of thromboembolic complications as they did not undergo PTRA.

RESULTS

Two hundred and two PTRAs were performed. The total volumes of contrast medium administered and the procedure durations were the same for each patient. In the ioxaglate group, four dissections (3 stents), one occlusive dissection, and two spasms occurred; in the iobitridol group, there were three dissections (all stented), one occlusive dissection (stented), and two spasms. The final angiograms showed four renal infarctions with ioxaglate (2 of which were in patients who were not anticoagulated), two with iobitridol. No significant difference was seen in the incidence of thromboembolic complications when the PTRA was performed after anticoagulation (n = 150; 3.9% vs 4%, p = 0.78); in the whole population, thromboembolic complications were more frequent in the ioxaglate group but the difference was not significant (5.7% vs 3.7%, p = 0.74). The quality of the diagnosis and the general and renal safety were the same in the two groups.

CONCLUSION

Regarding the clotting phenomenon, we recorded as many thromboembolic complications with ioxaglate as with iobitridol.

Thrombotic risk associated with the use of iodinated contrast media in interventional cardiology: pathophysiology and clinical aspects

A review of the current knowledge of the anti-thrombotic properties of iodinated contrast media (CM) has been conducted. CM are classified according to their chemical structure, either ionic or non-ionic (monomeric or dimeric). Numerous in vitro and in vivo data show that, although all CM have anti-coagulant properties, ionic molecules are more potent than non-ionic and, furthermore, do not activate resting platelets, unlike non-ionic agents. These properties may lead to a decrease in thrombus formation during interventional procedures. Several clinical trials have shown that CM may play a role in the occurrence of acute thrombotic complications but also in delayed ischaemic events during interventional procedures. A recent meta-analysis showed that, compared to non-ionic monomers, ionic low-osmolar CM reduce the rate of coronary artery abrupt closure, but no significant difference was found with respect to ischaemic complications. Ionic CM lead to a lower deposit of thrombotic materials on catheters and guide-wires. To date, clinical data comparing ionic CM and non-ionic dimers are scarce, significantly heterogeneous and, unlike experimental data, they do not show differences between both classes of CM. Further studies are required to better understand the precise mechanisms of such interactions and to analyse the effect of CM when new antiplatelet agents or new procedures (stenting) are used, to comply with new clinical strategies.

Effects of non-ionic monomeric and dimeric iodinated contrast media on renal and systemic haemodynamics in rats

Non-ionic dimeric contrast media (CM) are a new class of CM which are iso-osmolar with plasma. The aim of this study was to investigate their effects on systemic and renal haemodynamics. The non-ionic dimeric CM iodixanol and the non-ionic monomeric agent iobitridol (both at a dose of 1,600 mgI/kg) were compared in terms of their effects on systemic blood pressure (BP) and renal blood flow (RBF) in two strains of rats (Wistar and Sprague Dawley). Iodixanol significantly lowered BP in Wistar rats (-33 +/- 9% of baseline, 10 min post-injection, P < 0.001 vs. saline and iobitridol). Iobitridol had virtually no effect on BP. Iobitridol and iodixanol significantly decreased RBF. This effect was more marked following injection of the dimer rather than the monomer (iodixanol: -32 +/- 13% iobitridol: -20 +/- 4 of baseline at 16 min, P < 0.05). For both agents, RBF was still decreased 50 min following injection (iodixanol: -30 +/- 11%, and iobitridol: -20 +/- 5% of baseline). Iodixanol also decreased RBF in Sprague Dawley rats, while BP remained unchanged. This suggests that changes in BP/RBF autoregulation do not account for the renal haemodynamic effects of this agent. When measured 2 h following injection, the iodixanol-induced renal hypoperfusion was still detectable (-29% vs. saline-treated rats), although not significant (P = 0.06). This effect was no longer observed 4 h following injection. Increasing the saline infusion rate (18 mL/h vs. 2 mL/h) during the experiment did not significantly decrease the effects of iodixanol on BP and RBF in Wistar rats. In spite of its iso-osmolality, iodixanol, a non-ionic dimeric CM, depressed RBF and BP significantly more than iobitridol, a monomeric non-ionic agent, in Wistar rats. This effect was long-lasting and was not alleviated by increasing the hydration rate.

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.

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.

Comparative cytotoxicity of low- and high-osmolar contrast media to human fibroblasts and rat mesangial cells in culture

RATIONALE AND OBJECTIVES

The authors investigate the relative sensitivity of rat mesangial cells to iodinated contrast media (CM) and control solutions versus less differentiated cells (ie, human fibroblasts) and compare the effects of low-osmolar ionic (ioxaglate) and nonionic (iopamidol) and high-osmolar ionic (diatrizoate) CM on rat mesangial cells.

METHODS

The cytotoxic effects of ioxaglate and control solutions of sodium chloride and mannitol were assessed by neutral red uptake in isolated rat mesangial cells and human fibroblasts. In a second series of studies, the cytotoxic effects of ioxaglate, iopamidol, and diatrizoate (0 to 100 mg I/mL) on rat mesangial cells were compared.

RESULTS

Rat mesangial cells were more sensitive to the cytotoxic effects of ioxaglate than the less differentiated human fibroblasts between 70 and 100 mg I/mL. A similar discrepancy was observed in the case of control solutions, sodium chloride, and mannitol. Ioxaglate and iopamidol induced a similar level of cytotoxicity in rat mesangial cells whereas the high-osmolar agent diatrizoate was significantly more cytotoxic. However, the calculated inhibitory concentrations of 50% of all three CM were associated with similar osmolalities, suggesting a major role for this parameter in the case of such media.

CONCLUSIONS

Rat mesangial cells are more sensitive to the cytotoxic effects of CM and hyperosmolar solutions than the less differentiated human fibroblasts. High-osmolar CM are more cytotoxic than ionic and nonionic low-osmolar CM to rat mesangial cells. Ionicity seems to play no deleterious role at similar iodine concentrations because ioxaglate and iopamidol had equivalent cytotoxic effects on mesangial cells.

Iodinated contrast material in uroradiology. Choice of agent and management of complications

Many conditions seen by urologists require imaging examinations with iodinated radiographic contrast material as a key part of the primary evaluation of the patient. A basic understanding of contrast media, risks of administration, choice of agents, and premedication regimens for high-risk patients, is beneficial in helping patients prepare for their examinations. Urologists may be the primary physicians administering contrast material or may be working with radiologists in the care of patients receiving contrast agents. Because contrast reactions may occur unexpectedly, even during examinations in which the agents are not given intravenously, urologists should be able to recognize and treat the various types of adverse reactions.

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.

MR assessment of iodinated contrast-medium-induced nephropathy in rats using ultrasmall particles of iron oxide

The purpose of this study was to determine the diagnostic value of ultrasmall particles of iron oxide (USPIO)-enhanced MR imaging at different concentrations to evaluate experimental nephropathy. This study was conducted in 23 uninephrectomized rats using a model of iodinated contrast media-induced renal failure. Eleven rats received selective intra-arterial renal administration of diatrizoate (370 mg I/ml) and were compared to two control groups, including five animals injected with isotonic saline and seven noninjected animals. MR imaging was performed 28 hours after the procedure, including T1- and T2-weighted images before and after intravenous administration of successively 5 mumol Fe/kg and 60 mumol/kg of USPIO. Results were interpreted qualitatively and quantitatively with respect to pathologic data, and differences were studied statistically. The maximal signal intensity decrease was noted in normal kidneys in cortex (-65 +/- 4%) and medulla (-84 +/- 5%) on T2-weighted images after injection of 60 mumol/kg of USPIO. At this dose, diseased kidneys displayed less signal intensity decrease than normal kidneys on T2-weighted images (p = .05). Moreover, qualitative analysis showed that the highest sensitivity and specificity to diagnose kidney involvement were obtained with T2-weighted MR images (75% and 91%, respectively) when 60 mumol/kg of USPIO were used (p < .01). USPIO should be useful for in vivo evaluation of the severity of experimentally induced iodinated contrast media renal impairment in animals.

Effects of the low-osmolality contrast medium ioversol (Optiray) on renal function in a geriatric population

PURPOSE

To assess the incidence of nephrotoxicity following i.v. injection of the iodinated low-osmolality contrast medium ioversol 300 (Optiray) in a geriatric population compared with a control group aged under 60 years, neither group presenting any associated risk factors.

MATERIAL AND METHODS

CT with i.v. bolus injection of ioversol 300 mg I/ml was performed at a mean dose of 1.36+/-0.06 ml/kg (range 1-2 ml/kg b.w.) in 47 patients aged over 69 years. Serum creatinine level was measured and creatinine clearance was calculated at 24, 48 and 72 h after the examination, and compared to a reference serum creatinine value taken before CT. The findings were compared with a control group of 44 patients aged under 60 years.

RESULTS

No significant increase in serum creatinine (+0.6 mmol/l) or in creatinine clearance (+0.7 ml/min) was found during the course of 3 days after the injection. Only one patient (aged 82) presented an increase of 25% in serum creatinine (109 mmol/l).

CONCLUSION

The trial did not demonstrate any significant difference between the 2 groups, although the elderly patients had a subclinical renal impairment revealed by the decrease of the initial creatinine clearance. The use of low-osmolality ioversol makes it possible to perform examination with an iodinated contrast agent without increasing the incidence of nephrotoxicity in elderly subjects.

The acute effect of ioversol on kidney function: role of endothelin

The effect of ioversol, a non-ionic monomer with high hydrophilicity, on renal function was studied using the isolated perfused rat kidney (IPRK). The involvement of endothelin in the renal effect of ioversol was established pharmacologically using the selective endothelin ETA receptor antagonist BQ123. Ioversol 20 mgI/ml produced a sustained fall in both renal perfusate flow (RPF) and the glomerular filtration rate (GFR) together with a fall in sodium reabsorption (FRNa) and increase in urine flow (n = 6). In the presence of BQ123 (10 microM), the effect of ioversol 20 mgI/ml on GFR was completely abolished and the fall in RPF and FRNa markedly reduced (n = 6). These results suggest that effect of ioversol on renal haemodynamics in the IPRK is mediated by endothelin. Ioversol produced a significantly smaller decrease in GFR than iopromide, a contrast media with similar osmolality but lower hydrophilicity, when compared to a previous study using an identical experimental technique. Increased hydrophilicity may therefore present an advantage for ioversol, reducing its effects on renal function.