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

Pathophysiology of renal tissue damage by iodinated contrast media

1. The present review focuses on the cytotoxic effects of iodinated contrast media (CM) that are shared by all types of CM. 2. Although the clinical nephrotoxicity of CM has been progressively improved, all currently available CM still possess a level of cytotoxicity, which is probably caused by iodine. 3. The toxicity caused by specific CM properties, such as osmolarity, viscosity and ionic strength, can be differentiated from the cytotoxicity common to all CM in studies using cell culture, isolated blood vessels and isolated tubules. 4. The cytotoxicity induced by CM leads to apoptosis and cell death of endothelial and tubular cells and may be initiated by cell membrane damage, together with oxidative stress. 5. Cell damage may be aggravated by factors such as tissue hypoperfusion and hypoxia, properties of individual CM, such as ionic strength, high osmolarity and/or viscosity, and clinically unfavourable conditions. 6. Clinically detectable renal failure may result from the summation of all these factors.

Biomedical imaging in the safety evaluation of new drugs

Toxicology accounts for approximately one-third of attrition in new drug development and is a major concern in the pharmaceutical industry. This paper reviews the role of biomedical imaging in the safety evaluation of new candidate drugs. Ex vivo high-resolution three-dimensional imaging of specimens can provide a quick overview of the specimens. Volumetric measurements of tissue structures and lesions can be made with higher precision and reproducibility than histology approaches. As opposed to histology, in vivo animal imaging permits longitudinal studies of the same animals over an extended period of time, with individual animals serving as their own control. Therefore, the number of animals required for a study can be significantly reduced and the intra-subject variability is minimized. Repeated in vivo imaging allows monitoring of the occurrence and progression, or regression, of various structural and functional abnormalities. Compared with other biological assays, imaging can provide anatomically specific information about tissue abnormality. Imaging offers the opportunity to carry forward the same methodology in animal experiments into human studies and has an important role in clinical trials when other safety biomarkers for early toxicities are not available.

Safety and Hemodynamic Effects of Pulmonary Angiography in Patients with Pulmonary Hypertension: 10-Year Single-Center Experience

OBJECTIVE

We sought to examine the incidence of complications and change in pulmonary artery pressure in patients with pulmonary hypertension who were undergoing pulmonary angiography.

MATERIALS AND METHODS

A retrospective review was performed for all patients who underwent pulmonary angiography over a 10-year period at a single institution. Patients with moderate pulmonary hypertension (pulmonary artery pressure, 30-59 mm Hg) and severe pulmonary hypertension (pulmonary artery pressure, >/= 60 mm Hg) served as the study population. Demographic data, clinical indication, pre- and postcontrast pulmonary artery pressure measurements, type of pulmonary hypertension, contrast agent volume, complications, and American Society of Anesthesiologists (ASA) classification were recorded for all patients and compared.

RESULTS

Two hundred two of 612 patients who underwent pulmonary angiography had pulmonary hypertension. Moderate pulmonary hypertension was present in 155 patients (77%) and severe pulmonary hypertension, in 47 patients (23%). Three (2.0%) of four complications were fatal. The complication rate was higher in patients with severe pulmonary hypertension compared with patients with moderate pulmonary hypertension but not statistically significant (6.3% vs 0.6%, p = 0.63). Patients with complications had a higher mean ASA score than those without complications (4.0 vs 3.0, p = 0.03). Patients with lung transplants had the greatest increase in pulmonary artery pressure after pulmonary angiography compared with all other clinical indications (16.75 +/- 12.97 mm Hg vs 5.46 +/- 6.86 mm Hg, p = 0.003).

CONCLUSION

The complication rate of pulmonary angiography in patients with pulmonary hypertension is low. However, in severely ill patients with acute pulmonary hypertension, pulmonary angiography should be undertaken with extreme caution.

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.

Review article: Effects of radiographic contrast media on the lung

The pulmonary adverse effects of intravascular use of water soluble radiographic contrast media (RCM) include bronchospasm, pulmonary oedema and increase in the pulmonary arterial blood pressure (Ppa). Symptomatic bronchospasm is rare but subclinical increase in airways resistance is common after intravascular injection of RCM. Experimental studies have demonstrated that the low osmolar ionic dimer ioxaglate can induce significant bronchospasm in comparison with other types of RCM. Histamine and endothelin, which are potent bronchoconstrictors and released in response to the administration of RCM, do not seem to mediate the bronchospastic effect of RCM. Pretreatment with corticosteroids or antihistamine does not appear to prevent RCM induced bronchospasm, but the administration of beta(2) adrenergic agonist can abolish this adverse effect. RCM induced pulmonary oedema can be secondary to endothelial injury causing an increase in the permeability of the microcirculation. It may also occur in patients with incipient cardiac failure, when large doses of RCM particularly of the high osmolar type are used. A rise in Ppa induced by RCM seems to be secondary to an increase in pulmonary vascular resistance through direct effects on the pulmonary circulation. Low osmolar non ionic monomers induce the least changes in the pulmonary circulation and should be the contrast media of choice for intravascular use in patients with pulmonary hypertension. The mechanisms responsible for the effects of RCM on airway resistance and pulmonary circulation remain unclear. Intrabronchial administration of high osmolar water soluble RCM is dangerous and can induce severe bronchial irritation and pulmonary oedema. Low osmolar RCM are well tolerated by the lungs following aspiration with minimal histological reaction.

Effects of radiographic contrast media on pulmonary vascular resistance of normoxic and chronically hypoxic pulmonary hypertensive rats

Intravascular radiographic contrast media (RCM) can be associated with significant morbidity in patients with pulmonary hypertension (PH). This study investigated the direct effect of the four main classes of RCM (high osmolar ionic monomer "diatrizoate"; low osmolar ionic dimer "ioxaglate"; low osmolar non-ionic monomer "iopromide"; and iso-osmolar non-ionic dimer "iotrolan") in ex vivo isolated rat lungs perfused with blood at 20 ml min(-1) under basal conditions (air + 5% CO2 ventilation, pulmonary artery pressure (Ppa) 16-20 mmHg) and when Ppa was raised by hypoxic vasoconstriction in normal rats (2-3% O2+5% CO2 ventilation, Ppa increased by 4-14 mmHg). The effects of low osmolar RCM (ioxaglate, iopromide and iotrolan) were also studied in rats with PH induced by chronic hypoxia (3 weeks 10% O2, Ppa 26-36 mmHg). Increasing volumes (0.05 ml, 0.1 ml, 0.3 ml, and 0.5 ml) of RCM, mannitol (osmolar and pH control) or normal saline (volume control) were added to the 10 ml blood reservoir (n=4-9 per group). In normal rats, RCM caused a dose-dependent slow rise in Ppa. The maximum rise in mean+/-SEM Ppa at the cumulative dose of 0.95 ml was ioxaglate 13.8+/-1.6 mmHg>iotrolan 7.3+/-1.7 mmHg=diatrizoate 9.8+/-2.2 mmHg>iopromide 3.0+/-0.8 mmHg (p<0.05). The rise in Ppa induced by ioxaglate and iotrolan was significantly greater than in the mannitol and saline controls (p<0.05). Pre-treatment with endothelin receptor A/B blockade (SB209670) did not abolish the rise in Ppa induced by diatrizoate (0.95 ml) in the normal rat (3.8+/-1.3 mmHg diatrizoate alone and 3.4+/-1.1 mmHg in the presence of 40 microM SB209670, n=5 per group). When Ppa was raised by acute hypoxia, ioxaglate and diatrizoate (0.5 ml) caused a fall in Ppa (percentage fall -53+/-23 and -118+/-10, respectively, p<0.001) while iotrolan and iopromide caused a small further rise in Ppa, which was significant with iotrolan at a dose of 0.3 ml (percentage rise in pressure 14.2+/-2.3, p<0.05). In chronic pulmonary hypertensive rats, RCM (0.95 ml) caused an overall slow progressive rise in Ppa (iopromide 6.8+/-1.7 mmHg< ioxaglate 11.6+/-2.5 mmHg=iotrolan 12.7+/-1.1 mmHg). However, ioxaglate initially induced an acute fall of Ppa (maximum fall 4.22+/-0.9 mmHg, p<0.05) for almost 20 min. In summary, iopromide induced the least change in Ppa of normal and pulmonary hypertensive rats. The pathophysiology of the effects of RCM on the pulmonary circulation remains uncertain.

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 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.

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.

Ventilatory effects of radiographic contrast media

Respiratory adverse reactions have been reported with the use of contrast media. This study investigates the effects of different radiographic contrast media (RCM) on ventilation and blood gases. Tidal volume and respiratory rate of male Wistar rats anaesthetised with Inactin (100 mg kg-1 intraperitoneally), were measured continuously by integration of tracheal airflow. Contrast media (diatrizoate 370, ioxaglate 320 and iopromide 300) or mannitol controls matched for volume, pH and osmolarity (4 ml kg-1) were administered via a jugular cannula (n > or = 6 per group). Carotid artery blood was sampled at 2, 7, 12, 17, 25 and 30 min post-injection for PaO2, PaCO2 and pH. Systemic blood pressure was monitored from the same cannula. No significant reduction was observed in minute ventilation (tidal volume x respiratory rate per minute) with any of the contrast media. All contrast media and control solutions produced a fall in PaO2 within 4 min; returning to basal levels at 10 min (diatrizoate 35.6% (p < 0.05), ioxaglate 15.2% (p < 0.02), iopromide 16.2% (p < 0.01); controls: 17.3% (p < 0.01), 13.5% (p < 0.02) and 12.0% (NS), respectively). The fall in PaO2 induced by diatrizoate was significantly (p < 0.05) larger in comparison to the other groups. Ioxaglate, iopromide and their mannitol controls induced a comparable fall in PaO2. There was a concurrent rise in PaCO2 and fall in pH that reached significance for diatrizoate (p < 0.01). The changes in blood gases with RCM administration cannot be explained by changes in ventilation and may be due to an effect on pulmonary perfusion.