Animal evaluation of technetium-99m triamide mercaptide complexes as potential renal imaging agents

Technetium-99m mercaptoacetylglycylglycylglycine (MAG3), a [99mTc]triamide mercaptide (N3S) compound has been synthesized in an attempt to obviate the stereochemistry problems associated with the diamide dimercaptide (N2S2) ligands. Because initial studies have been promising, the terminal glycine on the MAG3 compound has been varied to create a new series of N3S compounds. Twelve new N3S complexes were initially screened in mice and the more promising complexes, 99mTc mercaptoacetylgylcylglycyl-glycine [( 99mTc]MAG3), 99mTc mercaptoacetylgylcylglycyl-L-alanine [( 99mTc]MAG2-Ala), and both complexes of 99mTc mercaptoeacetylglycylglycyl-L-asparagine [( 99mTc]MAG2-Asn) and 99mTc mercaptoacetylglycylglycyl-L-glutamine [( 99mTc]MAG2-Gln), were further evaluated in rats utilizing constant infusion blood clearances, extraction efficiencies and protein binding assays. The renal excretion of all these complexes compared favorably with simultaneously administered [131I]OIH and [125I]iothalamate. The triamide mercaptide complexes represent a new ligand class for 99mTc, which may provide a variety of complexes for the evaluation of renal tubular function.

Radiographic study of intercostal nerve blockade in healthy volunteers

The spread of solutions injected to the intercostal space was studied in 10 healthy volunteers. Up to 20 ml of a 50:50 mixture of local anaesthetic solution and a radiopaque dye was injected through a modified extradural catheter placed in an intercostal space at the posterior angle of the rib. Radiographic films demonstrated spread by an extrapleural route into adjacent intercostal spaces and this was confirmed by the occurrence of analgesia in the corresponding dermatomes. The relevance of these results to clinical practice is discussed.

Variability in arteriographic assessment of the carotid bifurcation

We evaluated interobserver and intraobserver variability in the arteriographic assessment of the carotid bifurcation. Two neuroradiologists evaluated area stenosis and lumen surface morphology for 60 biplane carotid arteriograms in two reading sessions. Absolute interobserver differences for area stenosis averaged 8.8%, and interobserver differences were statistically significant for arteries of at least 50% stenosis. Analysis of observations for lumen surface morphology revealed statistically significant interobserver differences, averaging 29.5% disagreement. Intraobserver differences were not statistically significant. Observer variability for arteriography should be considered in the process of evaluating patients for carotid endarterectomy.

The optic neurogram: evaluation of CSF "block" caused by compressive lesions at the optic canal

Patients with progressive blindness resulting from bony proliferative diseases such as osteopetrosis may benefit from optic canal decompression. A radiologic technique is described whereby the practicality of surgical optic canal widening is evaluated preoperatively using the intrathecal water-soluble contrast agent lopamidol. Conceptually, if a patient who is losing vision demonstrates a block on the optic neurogram, then likely there is still sufficient neural tissue within the optic canal and sheath to cause obstruction, and therefore decompression may be indicated. However, if preoperatively there is no block to lopamidol, then surgical intervention is not indicated, as the nerve has already undergone severe atrophy to the point of "autodecompression." Cases of differing etiologies, with and without blocks, illustrate the utility of the method and point out the importance of early surgical management to prevent irreversible damage to the optic nerve.

Renal hypertrophy in experimental diabetes: some functional aspects

Glomerular filtration rate (GFR) was measured by constant infusion of iothalamate in conscious rats with and without streptozotocin diabetes. Kidney weight had already increased significantly after 4 days of diabetes. GFR was unchanged at that time, but increased subsequently, so that GFR/kidney weight was normal after 1 month of diabetes. Tubular glucose reabsorption rate was increased to the same extent as kidney weight after 4 days of diabetes. It is concluded that renal growth in experimental diabetes cannot be initiated by glomerular hyperfiltration, but that increased glucose reabsorption may have a causal role.

Contrast enhancement of brain tumors and irradiated normal brain: a comparison of iohexol and iothalamate

The nonionic contrast agent iohexol was compared with the ionic agent iothalamate for contrast enhancement of brain tumors and radiation brain damage in dogs. Tissue enhancement during infusion of contrast and 5, 10, 15 and 30 min later was measured using quantitative computed tomography. Blood iodine was measured using x-ray fluorescence. Peak contrast enhancement occurred during infusion in tumors and after 5 min in irradiated normal brain for both contrast agents. Absolute uptake of contrast in each lesion was the same for both agents when normalized to total grams of iodine administered. Blood iodine levels were slightly but not significantly higher using iohexol. The reduced osmotic load and similar contrast enhancement of lesions suggest that the nonionic contrast medium iohexol may be a useful agent for routine CT of the brain.

Relative frequency of acentrics to dicentrics caused by radiation and by chemical action on human lymphocytes

Various concentrations of sodium iothalamate were added to human blood samples before exposure to X-rays, in order to investigate the dependence of the frequency ratio of acentrics to dicentrics on treatment with radiation, the drug and a combination of the two. The results show that this ratio is markedly influenced by the relative action of the two agents, at low radiation dose, because of the enhancement of the acentric frequency caused by the chemical substance with respect to the spontaneous level. This paper presents the experimental yields of aberrations corresponding to the various treatments, and the calculated frequency ratios of acentrics to dicentrics as a function of X-ray dose, after correction for the physical effect of dose enhancement due to the presence of iodine in the drug.

A comparison of simplified and standard methods for the measurement of glomerular filtration rate and renal tubular function

Two methods of measuring the clearance of 99Tcm DTPA, OIH and iothalamate were compared with standard techniques of measuring the clearance rates of inulin and sodium para-aminohippurate. The best correlation was between the clearance of subcutaneously injected radiolabelled iothalamate or 99Tcm DTPA and that of inulin. 99Tcm DTPA and 131I OIH clearances measured by a two blood sample technique did not give as good a correlation with inulin and PAH clearances respectively. When measurements of GFR and tubular function were repeated on the same patients the changes measured by inulin and PAH clearances did not correlate with those measured by the two blood sample technique using 99Tcm DTPA and OIH. Our results suggest that the clearance of subcutaneously injected iothalamate or DTPA can replace inulin clearance measurements. The two blood sample technique of measuring DTPA and OIH clearance does not directly reflect inulin and PAH clearance and is insufficiently reproducible to be used to follow changes in renal function.

Development of a fetal renal function test using endogenous creatinine clearance

Selecting appropriate management for the fetus with obstructive uropathy depends on our ability to accurately assess the severity of existing renal damage and to predict the potential for recovery of renal function if the obstruction is relieved. Diagnosis and treatment would be markedly enhanced by a simple, safe, quantitative fetal renal function test. To answer the question of whether endogenous fetal creatinine clearance (CrC) is an accurate measure of glomerular filtration rate (GFR) in the obstructed fetal kidney, we compared fetal CrC to a standard test for GFR--iothalamate clearance (IC). Six fetal lambs underwent unilateral ureteral ligation at 60 to 63 days gestation (term = 145 days). The contralateral unobstructed kidneys served as a control. At a second operation at 113 to 120 days, renal function was measured by hourly split urine collections for determination of CrC, IC, and fractional sodium excretion on each side over a 4-hr study period. There was excellent correlation of CrC with IC in all kidneys (r = 0.997, P less than 0.001, y = 1.14 x). Compared to the control side, the obstructed fetal kidneys had significantly decreased GFR and abnormal tubular function with marked sodium loss.(ABSTRACT TRUNCATED AT 250 WORDS)

Persistent wedge-shaped contrast enhancement of the kidney

A case with a single wedge-shaped high-density area of the kidney that persists after urography was observed by CT scan. This might be an aberrant form of acute renal failure with multiple wedge-shaped contrast enhancement.

Contrast media osmolality and plasma volume changes

A theoretical and experimental study of the plasma volume expansion consequent on the hyperosmolality of contrast media is presented. In the case of the ratio 1.5 media theory and experiment coincide closely but in the case of the ratio 3 media the observed changes exceed the predicted. It is proposed that this is due partly to the slower diffusion of the ratio 3 media out of the intravascular space and partly due to the fact that the osmotic load presented by these media is greater than would be expected from a study of their commercial solutions in which osmolality is reduced by molecular aggregation. The implications for the relative haemodynamic effects of different contrast media are discussed. The osmotic effects of contrast media also play a part in determining the image quality achievable in intravenous digital subtraction angiography (IV-DSA). It is predicted that ratio 3 contrast media will give better quality images in IV-DSA than ratio 1.5 media.

Assessment of compensatory renal function and [125I]iothalamate clearance in sheep

Compensatory renal function and sodium [125I]iothalamate clearance were studied in 4 adult Merino ewes. Renal clearances of inulin (CIN), iothalamate (CIOT), and p-aminohippurate (CPAH) were used to measure renal function before and 7 and 170 days after 50% and 75% reductions in renal mass. Renal mass reduction to 50% of normal was achieved by ligation of the right renal artery, and to 25% of normal by ligating the right renal artery and branches of the left renal artery. Renal function (CIN and CPAH) after 50% renal mass reduction was 78% of normal on postligation day (PLD) 7 and 64% of normal on PLD 170. This decrease in renal function between PLD 7 and 170 was significant (P less than 0.05). Renal function (CIN and CPAH) after 75% renal mass reduction was 55% of normal on PLD 7 and 48% on PLD 170; however, this decrease in renal function between PLD 7 and 170 was not significant. Results indicated that, shortly after 50% renal mass reduction by renal arterial ligation, renal function in ewes was greater than that previously reported after unilateral nephrectomy and that a further decrease in renal function developed within 6 months after ligation. The mean CIOT in healthy ewes was 2.46 ml/min/kg of body weight. In healthy ewes and in ewes after renal mass reduction, regression of the simultaneous CIOT and CIN was CIOT = 0.276 + 1.05 CIN. The CIOT was higher than the corresponding CIN, and remained significantly (P less than 0.01) and consistently higher. Therefore, iothalamate can be used to estimate glomerular filtration rate in sheep, although a correction factor is required.

Attenuation changes of the normal and ischemic canine kidney. Dynamic CT scanning after intravenous contrast medium bolus

The potential of CT scanning to explore total and regional renal blood flow was evaluated in a dog model with unilateral renal artery stenosis (n = 7, reduction of renal blood flow: 32-75% of base line flow). Attenuation versus time curves were generated for the renal cortex and medulla, as well as for the aorta and renal vein. A fast CT scanner was used which allowed for up to 24 scans/minute at the same level (slice thickness: 10 mm). A total of 10 ml contrast medium was injected into a peripheral vein for each scan series taken. During baseline conditions, the curve of the renal cortex and medulla demonstrated 2 peaks. The first peak was mainly related to early vascular enhancement, whereas the second peak corresponded mainly to the appearance of contrast medium in the distal convolutes and collecting ducts. Ischemia of the kidney resulted in a reduction of the first peak and a flattening of the leading edge slope. Transport of contrast medium through the extravascular compartments of the kidney was delayed during ischemia. Relative renal blood flow was obtained from the CT data by dividing peak enhancement by rise-time as assessed from the cortical curve. All measurements were related to baseline flow and validated by flow measurements using radioactive labeled microspheres (n = 5). Correlation was found to be r = 0.97.

Renal tubular accumulation of organic substances: a new in vivo method which differentiates between luminal and peritubular uptake

Using a modification of the Sperber technique we studied cellular uptake of organic substances in the kidney. A test substance was mixed with an extracellular marker (ethylenediaminetetraacetate or inulin), both radiolabelled with an activity ratio close to I, and injected into the renal portal system on one side via a leg vein. The animals were killed 1-10 min after injection and the radioactivity in different organs determined. Results showed significantly higher ipsilateral (injection) to contralateral (control) kidney ratios (substance to marker) at 1 min after injection for 125I-Na-o-iodohippurate (125I-Hipp; P less than 0.001), 14C-tetraethylammonium bromide (14C-TEA; P less than 0.001), 3H-dihydromorphine (3H-DHM; P less than 0.01), and 125I-iothalamate (P less than 0.01), with a progressive decrease in injection kidney ratios for 125I-Hipp and 14C-TEA when death occurred after a longer period. Inhibition of renal tubular transport with novobiocin or mepiperphenidol markedly reduced 1- and 4-min injection kidney ratios for 125I-Hipp and 14C-TEA, respectively. When death occurred after a longer period, ratios in both kidneys increased significantly for 125I-iothalamate. A good correlation was found between peak cellular accumulation in the kidney and excretion efficiency of test substances. Thus, the results indicate that 125I-Hipp, 125I-iothalamate, 14C-TEA, and 3H-DHM were accumulated from the peritubular side of the nephron through the transport systems for organic acids and bases, respectively, and that 125I-iothalamate also showed luminal uptake. In conclusion, this new in vivo technique is simple and well suited for studying renal tubular accumulation of organic substances and offers the advantage of being able to distinguish luminal from peritubular uptake.

Inaccuracy of estimated creatinine clearance for prediction of iothalamate glomerular filtration rate

The clinical practice of estimating creatinine clearance (Ccr) from a patient's serum creatinine value by use of various nomograms and prediction formulas is widespread. The predictive accuracy of such Ccr estimates as substitutes for measured values of glomerular filtration rate (GFR) has not been determined. In addition, the effect of patient physical parameters on GFR prediction accuracy has not been assessed. To investigate these issues, 500 predicted Ccr values from each of four versions of the formula of Cockcroft and Gault were statistically compared with GFR values measured by sodium iothalamate clearance (Cio) in 394 human subjects representing every level of renal function. We conclude that (1) the original formula of Cockcroft and Gault is an inaccurate predictor of GFR; (2) correction of the formula for patient physical parameters does improve its accuracy for GFR prediction; (3) the best formula is not accurate enough to replace laboratory measurement of GFR; and (4) GFR prediction inaccuracy is more often associated with extremes in patient age, weight, serum creatinine, body surface area, and measured GFR but may occur for any value of each of these parameters.

Newer contrast agents for urography

New low-osmolality ratio-3 contrast media have been shown to have less toxicity than currently used contrast media. In intravenous excretory urography, these agents give significantly higher urinary iodine concentrations, produce less diuresis, and are better tolerated by patients because of fewer unpleasant side effects. These newer low-osmolality contrast media have significant advantages in intravenous urography.

Membranoproliferative glomerulonephritis. A prospective clinical trial of platelet-inhibitor therapy

Forty patients with Type I membranoproliferative glomerulonephritis were treated for one year with dipyridamole, 225 mg per day, and aspirin, 975 mg per day, in a prospective, randomized, double-blind, placebo-controlled study. At the base line, the half-life of 51Cr-labeled platelets was reduced in 12 of 17 patients. The platelet half-life became longer and renal function stabilized in the treated group, as compared with the placebo group, suggesting a relation between platelet consumption and the glomerulopathy. The glomerular filtration rate, determined by iothalamate clearance, was better maintained in the treated group (average decrease, 1.3 ml per minute per 1.73 m2 of body-surface area per 12 months) than in the placebo group (average decrease, 19.6). Fewer patients in the treated group than in the placebo group had progression to end-stage renal disease (3 of 21 after 62 months as compared with 9 of 19 after 33 months). The data suggest that dipyridamole and aspirin slowed the deterioration of renal function and the development of end-stage renal disease.

Comparative study of glomerular filtration rate with diverse labelled agents

Clearances of 113mIn-EDTA, or 99mTc -DTPA or 131I-iothalamate were compared with 3H-inulin simultaneously in rabbits or dogs. The classical plateau method was explored followed by a second slope in some instances or by the single shot procedure in others. A two-compartmental mathematical model was always employed to compare and calculate. The study suggests that the diverse agents tested are handled following similar homeostatic trends and values, although the intervening membranes may act upon them individually with diffusion rates that may vary in relation to each substance, in particular at a given time interval.

[The effect of the injection of water-soluble triiodized monomer contrast media for intravenous urography on glomerular filtration, uricemia and urinary elimination of uric acid in normal subjects]

One mechanism suggested as being the cause of nephrotoxicity following the administration of triiodized contrast media is intratubular urate precipitation. Thirty healthy volunteers were investigated by IVU using three different media. The iodized injections (0,56 g/kg) failed to produce significant modifications of glomerular filtration and were followed by only very moderate variations in blood and urine uric acid levels.

Significance of contrast enhancement in cranial computerized tomography after subarachnoid hemorrhage

Eighty patients with subarachnoid hemorrhage underwent computerized tomography (CT) scanning before and after administration of Conray contrast medium. Abnormal enhancement was seen in visual evaluation of the CT scans in 26 cases, in the regions bordering the subarachnoid spaces. Abnormal enhancement was associated with a poor clinical condition, angiographic spasm, and a poor outcome. Measurements of absorption values in the thalamus revealed significant increases in density after contrast enhancement in those patients whose scans showed abnormal enhancement in the regions bordering the subarachnoid spaces on visual evaluation. The authors suggest that the abnormal enhancement is parenchymal, in the gyri, and is not "subarachnoid." They suggest that it is due to gyral hyperemia or extravasation of contrast material into the cortex resulting from breakdown of the blood-brain barrier, or a combination of both factors.

Iohexol in urography

Thirty patients injected intravenously with a nonionic contrast medium, iohexol, for urography were compared with 30 patients similarly injected with sodium iothalamate. Comparable radiographic results were obtained in these patients with normal renal function. Few minor responses were observed with the iohexol, suggesting that it may prove to be an attractive contrast medium for this purpose.