Role for endothelin in the renal responses to radiocontrast media in the rat

Effect of theophylline on prevention of contrast-induced acute kidney injury: a meta-analysis of randomized controlled trials

BACKGROUND

Whether treatment with adenosine receptor antagonists such as theophylline can prevent contrast-induced acute kidney injury (AKI) remains controversial.

STUDY DESIGN

We conducted a meta-analysis of randomized controlled trials using MEDLINE (1966 to July 2011), EMBASE (1980 to July 2011), Web of Science (1986 to July 2011), and the Cochrane Central Register of Controlled Trials (1996 to July 2011), without language restriction.

SETTING & POPULATION

Patients undergoing contrast procedures.

SELECTION CRITERIA FOR STUDIES

Randomized controlled trials assessing adenosine antagonists versus control for prevention of contrast-induced AKI.

INTERVENTION

Adenosine antagonists with or without N-acetylcysteine versus control with or without N-acetylcysteine.

OUTCOMES

Contrast-induced AKI, change in serum creatinine level, requirement of dialysis, and in-hospital mortality.

RESULTS

16 trials (1,412 participants) were included. Theophylline significantly decreased the risk of contrast-induced AKI (13 trials, 1,222 patients; risk ratio, 0.48; 95% CI, 0.26-0.89; P = 0.02; I(2) = 45%) and had a protective effect on the absolute change in serum creatinine concentration (13 trials, 1,170 patients; standardized mean difference, -0.31 mg/dL; 95% CI, -0.50 to -0.11; P = 0.002; I(2) = 60%). Meta-regression showed a significant relation between the relative risk of contrast nephropathy and baseline serum creatinine level or Jadad score. No clear effects of treatment on risk of dialysis and in-hospital mortality were identified.

LIMITATIONS

Power to assess clinical end points was limited.

CONCLUSIONS

Theophylline treatment significantly reduced the incidence of contrast-induced AKI and had a modest improvement on kidney function after contrast exposure in the general population. However, beneficial effects of theophylline were not observed in patients with high baseline creatinine values (serum creatinine ≥1.5 mg/dL). In addition, the long-term effect of this agent on more clinically important outcomes was not established. Future large-scale high-quality multicenter trials in participants with different underlying risks of contrast-induced AKI and that incorporate the evaluation of clinically relevant outcomes are required.

Prophylaxis of contrast material-induced nephropathy in patients in intensive care: acetylcysteine, theophylline, or both? A randomized study

PURPOSE

To prospectively compare the protective effect of acetylcysteine, theophylline, and both agents combined in patients who are admitted to the intensive care unit with at least one risk factor for contrast material-induced nephropathy and who receive at least 100 mL of iodinated contrast medium.

MATERIALS AND METHODS

Institutional ethics review board approval and informed consent were obtained. A total of 91 patients (mean age, 58.5 years+/-14.8 [standard deviation]; 31 women, 60 men; 150 examinations) were admitted to the intensive care unit with at least one risk factor for contrast-induced nephropathy and received either (a) 200 mg theophylline 30 minutes before contrast medium administration (group T), (b) 600 mg acetylcysteine twice daily on the day of and (if possible) the day before the examination (group A), or (c) both agents combined (group AT). The primary endpoint for this study was the incidence of contrast-induced nephropathy (chi2 test).

RESULTS

Groups T, A, and AT were comparable with regard to baseline creatinine levels and the amount of contrast medium administered. The incidence of contrast-induced nephropathy in groups T, A, and AT was 2%, 12%, and 4%, respectively, and was significantly lower in group T than in group A (P=.047). There was no significant difference in the incidence of contrast-induced nephropathy between groups A and AT (P=.148) or between groups T and AT (P=.53). For group A, serum creatinine did not change after 12, 24, or 48 hours compared with baseline. Creatinine levels in group T decreased 12 hours (1.19 mg/dL+/-0.58; P=.008) and 48 hours (1.16 mg/dL+/-0.55; P=.034) after contrast material injection compared with baseline (1.25 mg/dL+/-0.61). In group AT, creatinine significantly decreased 24 hours (1.21 mg/dL+/-0.74; P=.003) and 48 hours (1.17 mg/dL+/-0.69; P<.001) after contrast material injection compared with baseline (1.28 mg/dL+/-0.74). Group A had significantly higher maximal increases in creatinine than groups T and AT (P=.014).

CONCLUSION

For prophylaxis of contrast-induced nephropathy in patients who are admitted to the intensive care unit and who receive 100 mL or more of contrast medium, theophylline is superior to acetylcysteine.

Concomitant drugs with exposure to contrast media

The increasing number of radiological procedures performed in old patients with high co-morbidity may be one of the problems physicians have to deal with when regarding the increasing number of acute renal failures. A key question when addressing the patients scheduled to receive iodinated contrast media (CM) is which concomitant medications prescribed to the patient are potentially harmful or helpful in terms of the risk of contrast-induced nephropathy. This overview summarizes the knowledge of concomitant medications in the setting of CM application and gives suggestion for prescription. In general, due to the unique (yet not fully understood and of high complexity) mechanism of renal damage proposed for a variety of nephrotoxic drugs including CM, physicians should carefully monitor patients' renal function and hydration status whenever concomitant nephrototoxic drugs are used. Recommendations are to monitor kidney function with more sensitive measurements of glomerular filtration rate (i.e. cystatin C).

Prevention of Contrast Media–induced Nephrotoxicity after Angiographic Procedures

Contrast medium-induced nephrotoxicity (ie, contrast nephrotoxicity [CN]) remains an important complication of angiographic procedures. If administration of iodinated contrast medium is deemed necessary in patients at high risk of CN, volume expansion should be offered and the lowest possible dose of nonionic isosmolar dimeric or nonionic low-osmolar monomeric contrast medium should be used. Prophylactic administration of fenoldopam or acetylcysteine has not offered consistent protection against CN. Intravenous acetylcysteine could be considered in emergency situations. Recently, sodium bicarbonate infusion has been shown to reduce the risk of CN. Hemofiltration for several hours before and after contrast medium injection may offer good protection against CN in patients with advanced renal disease. Prophylactic hemodialysis does not offer any protection against CN.

Effects of Dimeric Radiographic Contrast Medium Iotrolan on Swine Renal Arteries

RATIONALE AND OBJECTIVES

To investigate whether the lower incidence of vasodilatation upon vascular injection of iotrolan, as compared with monomeric contrast media, is solely the result of its isotonicity.

MATERIALS AND METHODS

In an organ bath, isolated segments of swine renal arteries, uncontracted or precontracted by 10 microm phenylephrine, were incubated with increasing concentrations of iotrolan-300, iohexol-300, iomeprol-300, iomeprol-150, and mannitol solutions with the same molarity as the contrast media.

RESULTS

At equal iodine and equimolar concentrations, iotrolan-300 relaxed precontracted arteries less than iohexol-300, iomeprol-300, and iomeprol-150, which was, like iotrolan-300, iso-osmolar to blood (P < 0.05). There was no significant difference between iohexol-300 and iomeprol-300 (P > 0.05). Iotrolan had no significant effect on the basal tonus of the vessels whereas iohexol and iomeprol induced a slight relaxation.

CONCLUSIONS

Iotrolan, even at equimolar concentrations, resulted in less vasorelaxation than iohexol and iomeprol. Both osmolarity and chemotoxicity contribute to the greater vasorelaxant effect on swine renal artery of monomeric contrast media when compared to that of the nonionic dimeric contrast medium, iotrolan.

Prevention of contrast media nephrotoxicity--the story so far

Contrast media nephrotoxicity (CMN) in patients with pre-existing renal impairment remains a clinically significant problem. The first step to reduce the chance of CMN is to identify patients at risk through the use of screening questionnaires and renal function measurement. Patients at risk requiring injection of contrast medium (CM) because of important clinical indications should receive a small dose of either non-ionic iso-osmolar dimeric or non-ionic low osmolar monomeric CM and hydration. Intravenous infusion (1 ml/kg body weight/h) of 0.9% saline starting 4 h before CM injection and continuing for at least 12 h afterwards is effective in reducing the incidence of CMN. Prophylactic haemodialysis does not lower the risk of this complication. The value of pharmacological manipulation with renal vasodilators (calcium channel blockers, dopamine, atrial natriuretic peptide, fenoldopam (selective dopamine-1 receptor agonist), prostaglandin E(1), non-selective adenosine receptors antagonist (theophylline), non-selective endothelin receptor antagonist or the antioxidant acetylcysteine has not been fully proven. However, haemofiltration for several hours before and after contrast medium injection offers good protection against CMN in patients with advanced renal disease.

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.

Interactions between vasoconstrictors and vasodilators in regulating hemodynamics of distinct vascular beds

We examined whether interactions between angiotensin II (Ang II), endothelin (ET), nitric oxide (NO), and prostaglandins (PGs) differentially regulate perfusion to distinct vascular beds. For this, we blocked either angiotensin AT1 or ET receptors or both and then sequentially inhibited NO and PG synthesis in anesthetized dogs. Blocking Ang II or ET had similar effects on systemic hemodynamics: Mean arterial pressure fell slightly without altering cardiac output. Blocking both caused a synergistic fall in mean arterial pressure and increased cardiac output. Pulmonary vascular resistance was not altered by blocking Ang II, ET, or both but progressively increased during NO and PG blockade in group 2 (which had unblocked ET receptors), suggesting that endogenous ET exerts pulmonary vasoconstriction that is tempered by NO and PGs. In the kidney, blocking Ang II increased regional blood flow (RBF), glomerular filtration rate (GFR), and fractional excretion of sodium (FENa). In contrast, blocking ET did not alter RBF, and it decreased GFR and FENa. Combined Ang II and ET blockade markedly increased RBF without altering GFR, and FENa was maintained at the levels as when only ET was blocked. Sequentially inhibiting NO and PGs decreased RBF when Ang II or ET were blocked but had little effect when both were blocked. Finally, Ang II or ET blockade did not alter iliac blood flow. Inhibiting NO and PGs decreased iliac blood flow when Ang II or ET but not both were blocked. These results suggest that regional differences in the interactions between endogenous Ang II, ET, NO, and PGs are important determinants in systemic, pulmonary, and regional hemodynamics.

Altered response in renal blood flow and oxygen tension to contrast media in diabetic rats

PURPOSE

To investigate the effect of the contrast medium (CM) iopromide on renal microcirculation and oxygen tension in non-diabetic control and streptozotocin-diabetic Wistar Furth rats.

MATERIALS AND METHODS

Oxygen tension was measured with Clark-type microelectrodes and blood flow with laser-Doppler flow probes. In order to differentiate between an acutely increased blood glucose concentration and a long-term diabetic state, some of the non-diabetic control rats were intravenously infused with glucose.

RESULTS

CM decreased the medullary oxygen tension in control (non-diabetic normoglycemic) rats ( approximately 35%) but not in diabetic rats. Medullary blood flow in control rats increased after CM administration and remained elevated, while it was unchanged in the diabetic rats. In response to CM, glucose-infused control rats responded similarly to control animals in medullary oxygen tension, but similarly to diabetic rats in medullary blood flow. Contrary to in control rats, medullary oxygen tension was unchanged in diabetic animals after CM administration.

CONCLUSION

Streptozotocin-diabetic rats have an altered response to intravenous injection of the CM iopromide compared to non-diabetic rats. The unaltered medullary oxygen tension, seen in the diabetic group after injection of CM, suggests that non-hemodynamic mechanisms are responsible for the increased frequency of renal failure commonly seen among diabetic patients.

A randomized controlled trial of N-acetylcysteine to prevent contrast nephropathy in cardiac angiography

BACKGROUND

Contrast nephropathy (CN) is a common cause of renal dysfunction after cardiac angiography. Recently, N-acetylcysteine (NAC) has been found to reduce the risk of CN after CT imaging with contrast enhancement. The purpose of the current study was to evaluate the efficacy of NAC for the prevention of CN in the setting of cardiac angiography.

METHODS

Eligible patients were those undergoing cardiac angiography with serum creatinine>1.7 mg/dL. Patients were randomized to one of two groups: Group 1, IV hydration and NAC, 1200 mg one hour before angiography, and a second dose 3 hours after; Group 2, IV hydration and placebo. CN was defined as an increase of 0.5 mg/dL in serum creatinine.

RESULTS

Seventy-nine patients completed the study. There were no significant differences between the groups in baseline characteristics, duration of angiography, mean volume of dye infused or mean IV hydration. Contrast nephropathy developed in 24.0% of subjects, 26.3% NAC, and 22.0% placebo (P = NS). Among subjects with diabetes mellitus, there was no significant difference in the rate of CN between the groups (42.1% NAC, 27.8% placebo; P = 0.09). The independent predictors of CN risk were diabetes mellitus and preexisting chronic renal insufficiency.

CONCLUSIONS

NAC was not effective for the prevention of CN after cardiac angiography.

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.

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.

The effect of antihistamine, endothelin antagonist and corticosteroid prophylaxis on contrast media induced bronchospasm

Bronchospasm is a well recognized adverse reaction to radiographic contrast media (RCM) and may occur more frequently in asthmatics and atopics. This study was designed to identify RCM which are most likely to cause bronchospasm and to investigate underlying mechanisms mediating this response. Guinea pigs (mean body weight 550 g, n = 46) were anaesthetized with Hypnorm (5 ml kg-1) and Hypnovel (2 ml kg-1) and tracheal, jugular and pleural cannulae introduced. Total airways resistance (Raw) was calculated from the slope of the pressure/flow relationship. The effects of RCM (diatrizoate 370 mgI ml-1, ioxaglate 320 mgI ml-1, iotrolan 300 mgI ml-1 and iopromide 300 mgI ml-1) at a dose of 4 ml kg-1 body weight or control solutions matched for volume, pH and osmolarity administered via the jugular vein on Raw were studied. The effects of pre-treatment (30 min before the administration of RCM) with antihistamine (Mepyramine (30 mg kg-1 i.p.)) or non-selective endothelin receptor antagonist (SB209670 (1 mg kg-1 i.v.)) were investigated. The effectiveness of corticosteroids prophylaxis (prednisolone (20 mg kg-1 i.p.)) administered 18-24 h and 1 h pre-RCM was also assessed. Control animals received normal saline pre-treatment before RCM administration. Lungs were taken for histological examination 30-40 min post-administration of RCM. Only ioxaglate caused a significant (p < 0.05) increase in Raw (5.19 +/- 0.58 to 13.95 +/- 3.53 mmHg ml-1 min-1). Neither mannitol nor saline control solutions had any effect on Raw. Pre-treatment with Mepyramine, SB209670 or prednisolone caused no significant change in the ioxaglate induced increase in Raw. Histological examination of lung tissue from ioxaglate treated animals showed no important abnormalities. In summary, only the ionic dimer ioxaglate caused an increase in Raw. This effect was independent of osmolarity and could be the result of the chemical composition of the contrast agent. It was not an inflammatory response and could not be prevented by prophylactic treatment with antihistamine, endothelin antagonist or corticosteroids. The mechanisms responsible for the increase in Raw remain uncertain.

Effects of radiocontrast, mannitol, and endothelin on blood pressure and renal damage in the aging male spontaneously hypertensive rat

RATIONALE AND OBJECTIVES

The purpose of this research was to study the effects of the radiocontrast medium (CM) Hypaque-76 (diatrizoate meglumine sodium), equiosmolar mannitol, and endothelin on blood pressure and renal damage in a aging male spontaneously hypertensive rat, a small animal model for CM-induced renal damage. The importance of the pressor effect and the high osmolality of CM in producing renal damage was investigated by first reducing the blood pressure with pentobarbital anesthesia, which suppresses sympathetic nervous system activity, then testing the effects of CM, saline, mannitol, and the potent vasoconstrictor endothelin alone and in combination with CM.

METHODS

Systolic blood pressure was measured in 14-month-old male rats (1) when awake, (2) after pentobarbital anesthesia, (3) after the administration of saline, CM, mannitol, endothelin, or CM plus endothelin, (4) after awakening the same day, and (5) the following day while awake. Renal damage was quantified by evaluating histopathologically the left kidney removed the day after administration of test substances.

RESULTS

The pentobarbital-lowered blood pressure remained depressed after saline and mannitol but rose dramatically after CM, endothelin, and CM plus endothelin. Renal damage, compared with the saline controls, occurred with CM, mannitol, endothelin, and endothelin plus CM. The order of increasing severity was mannitol = CM < endothelin < endothelin plus CM.

CONCLUSIONS

The effect of CM on systolic blood pressure is not related to its osmolality. High osmolality, however, appears to be a factor in CM-induced renal damage. Ischemia and direct nephrotoxicity are factors contributing to the renal-damaging effects of CM, mannitol, and endothelin.

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.

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.

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.

Effects of radiocontrast and endothelin administration on systolic blood pressure and renal damage in male spontaneously hypertensive and Wistar Kyoto rats with phentolamine-induced adrenergic blockade

RATIONALE AND OBJECTIVES

The systemic administration of hypertonic solutions may activate the adrenergic system, thus triggering vasomotor reactions that may result in renal failure. In this study, the effects of diatrizoate meglumine sodium radiocontrast agent Hypaque-76 on systolic blood pressure (BP) and renal damage were determined in male spontaneously hypertensive (SH) rats and Wistar Kyoto (WKY) rats under adrenergic blockade.

METHODS

The systolic BP was measured in ketamine-anesthetized male SH and WKY rats after administration of saline solution, radiocontrast, or endothelin during adrenergic blockade with phentolamine. Then the left kidney was removed and examined histologically.

RESULTS

The fall in systolic BP after phentolamine was not influenced by saline solution or radiocontrast in WKY rats but was restored partially by radiocontrast in SH rats. Endothelin produced an elevation in BP toward baseline levels in both strains. Only moderate renal damage was observed in the kidneys of WKY rats given radiocontrast or endothelin, but very severe damage was produced by these agents in SH rats.

CONCLUSIONS

Adrenergic blockade with phentolamine did not prevent the elevation in systolic BP in SH rats by radiocontrast or by endothelin in SH and WKY rats, nor did it protect against renal damage by radiocontrast or by endothelin in SH rats.

Effects of radiographic contrast media on the tension of isolated small pulmonary arteries

The aim of the study was to establish the direct effects of radiographic contrast media (RCM) on the tension of isolated small pulmonary arteries and to investigate any mediation by nitric oxide (NO) and endothelin (ET). Small pulmonary arteries (0.3-0.6 mm in diameter) from male Wistar rats were mounted in a Cambustion vessel myograph and vessel wall tension recorded. The effects of 10, 20, 40, 80, 150, 200 and 250 mgl mI-1 of diatrizoate, ioxaglate, iopromide and iotrolan and their mannitol osmolar control from basal condition, and when the vessels were preconstricted with prostaglandin F2 alpha (PGF2 alpha) either submaximally (10 microM) or maximally (100 microM), were studied. The constrictor response to diatrizoate (40 mgI ml-1) was tested in the presence of non-selective endothelin receptor antagonist (10 microM SB209670). The dilator response to ioxaglate (80 mgI ml-1) was tested in the presence of L-nitroarginine methyl ester (L-NAME, 100 microM). All RCM caused biphasic changes in tension, a small transient fall (dilatation) followed by a sustained rise (constriction). Mannitol caused constriction only. The potency order of constrictions at 10-40 mgI ml-1 was diatrizoate > iopromide > ioxaglate > iotrolan. When the vessels were preconstricted with PGF2 alpha, RCM caused predominantly dilatation; ioxaglate produced the largest effect (-42.1 +/- 3.1%, n = 12). Mannitol caused constriction only. SB209607 had no effect on the constrictor effect of diatrizoate [41.9 +/- 2.3 alone, 42.1 +/- 2.7 with SB209670, n = 10]. L-NAME had no effect on the dilator response to ioxaglate [-38.2 +/- 1.6 alone, -43.6 +/- 2.2 with L-NAME, n = 8]. It is tempting to postulate that dimeric RCM may cause the least changes in the pulmonary circulation during angiography.

Effect of radiographic contrast media on endothelium derived nitric oxide-dependent renal vasodilatation

The effect of diatrizoate (Urografin325) on the cumulative dose-response curve of the vasodilatory response to acetylcholine was studied in the isolated perfused rat kidney (IPRK). The effect of 1-nitroarginine methyl ester (L-NAME) (10 mumol l-1) on the cumulative concentration-response curve of the vasodilatory response to acetylcholine and sodium nitroprusside was also studied. Acetylcholine is a vasodilator dependent on nitric oxide (NO) synthesis by the endothelium; sodium nitroprusside is a vasodilator not dependent on endogenous NO synthesis and L-NAME is an inhibitor of endogenous NO synthesis. The effect of L-NAME (10 mumol l-1) on the vasodilatory effect of diatrizoate which is observed in the presence of endothelin A receptor antagonist (BQ123, 10 mumol l-1) was also studied. In all experiments an infusion of angiotensin II (5 ng min-1) was maintained to increase the vascular tone of the preparation. Acetylcholine induced vasodilatation and the maximum increase in renal perfusate flow (RPF) was 17.0 +/- 1.7%, (p < 0.05). Diatrizoate (20 mgl ml-1 perfusate concentration) which induced a sustained fall in the RPF (-31.0 +/- 1.7%, p < 0.05) had no effect on the vasodilatory response to acetylcholine, and a similar increase in the RPF (17.8 +/- 2.2%, p < 0.05) was observed. In contrast, L-NAME (10 mumol l-1) completely abolished the vasodilatory effect of acetylcholine and produced instead a modest decrease in RPF by -5.0 +/- 1.7% (p < 0.05). The vasodilatory effect of sodium nitroprusside was not affected by L-NAME, confirming its selectivity as an inhibitor of endogenous NO synthesis in the IPRK. The maximum increase in the RPF induced by sodium nitroprusside was 23.1 +/- 2.0% (p < 0.05) in the absence of L-NAME and 21.2 +/- 2.2% (p < 0.05) in its presence. L-NAME did not interfere with the vasodilatation induced by diatrizoate in the presence of BQ123. In the presence of BQ123 alone the RPF increased from 23.3 +/- 1.4 ml min-1 g-1 to 26.5 +/- 1.0 ml min-1 g-1 (p < 0.05). In the presence of L-NAME and BQ123 the RPF increased from 24.4 +/- 3.0 ml min-1 g-1 to 27.2 +/- 2.7 ml min-1 g-1 (p < 0.05). There was no difference between the two groups (p > 0.05). In conclusion, diatrizoate did not interfere with endothelium derived NO-dependent vasodilatation in the kidney. A reduced production of NO in the vascular endothelium induced by contrast media is unlikely to play any role in the pathophysiology of the increase in renal vascular resistance produced by these agents. The renal vasodilatation induced by diatrizoate is not dependent on endogenous production of NO.

Endothelins in the normal and diseased kidney

Endothelin-1 (ET-1) is a 21-amino acid peptide that potently modulates renal function. ET-1 is produced by, and binds to, most renal cell types. ET-1 exerts a wide range of biologic effects in the kidney, including constriction of most renal vessels, mesangial cell contraction, inhibition of sodium and water reabsorption by the nephron, enhancement of glomerular cell proliferation, and stimulation of extracellular matrix accumulation. ET-1 functions primarily as an autocrine or paracrine factor; its renal effects must be viewed in the context of its local production and actions. This is particularly important when comparing ET-1 biology in the nephron, where it promotes relative hypotension through increased salt and water excretion, with ET-1 effects in the vasculature, where it promotes relative hypertension through vasoconstriction. Numerous studies indicate that ET-1 is involved in the pathogenesis of a broad spectrum of renal diseases. These include those characterized by excessive renal vascular resistance, such as ischemic renal failure, cyclosporine (CyA) nephrotoxicity, radiocontrast nephropathy, endotoxemia, rhabdomyolysis, acute liver rejection, and others. ET-1 appears to play a role in cell proliferation in the setting of inflammatory glomerulonephritides. The peptide also may mediate, at least in part, excessive extracellular matrix accumulation and fibrosis occurring in chronic renal failure, diabetes mellitus, and other disorders. Deranged ET-1 production in the nephron may cause inappropriate sodium and water retention, thereby contributing to the development and/or maintenance of hypertension. Finally, impaired renal clearance of ET-1 may cause hypertension in patients with end-stage renal disease. Many ET-1 antagonists have been developed; however, their clinical usefulness has not yet been determined. Despite this, these agents hold great promise for the treatment of renal diseases; it is hoped that the next decade will witness their introduction into clinical practice.

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.

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.