[Pharmacology of oral cholecystography].
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Chemical Phenomena↗
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Results for “IOPANOIC ACID”
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Additive nephrotoxicity from roentgenographic contrast media. Its occurrence in phenazopyridine-induced acute renal failure.
A 68-year-old woman had reversible nonoliguric acute renal failure and yellow pigmentation of her skin and sclerae after ingesting phenazopyridine hydrochloride, 200 mg four times a day for six weeks. Although she began to recover renal function promptly after the drug therapy was discontinued, there was a further decline in her glomerular filtration rate after an oral cholecystogram and intravenous pyelogram. Phenazopyridine-induced acute renal failure is rare, but its early recognition is important so that additional nephrotoxicity from studies using roentgenographic contrast material may be avoided in patients with this problem.
Acute Kidney Injury↗
Unusual cause of nonopacification of the gallbladder during oral cholecystography.
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Administration, Oral↗
[Cholangiography--a study of cholangiographic mechanism for improved visualization].
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Bile↗
Comparison of oral and ultrasound cholecystography.
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Adult↗
Drug and fatty acid effects on serum thyroid hormone binding.
We directly compared the competitor potency for serum T4 binding of 11 nonsteroidal antiinflammatory drugs; the diuretics furosemide, ethacrynic acid, and bumetanide; diphenylhydantoin; the cholecystographic contrast agents iopanoate and ipodate; and six long-chain nonesterified fatty acids (NEFA) using equilibrium dialysis. To avoid artefacts that occur in competitor studies with diluted serum or isolated binding proteins, we used undiluted normal serum, with drugs added at concentrations that achieved high therapeutic total and free serum levels at equilibrium. Drug addition was based on the measured free fraction of each drug in serum. The free T4 fraction in normal serum (Tris buffer, pH 7.4; 37 C) was between 1.40 X 10(-4) and 1.53 X 10(-4). Drug-induced increases in T4 free fraction were: fenclofenac, 90%; aspirin, 62%; meclofenamic acid, 39%; diflunisal, 37%; mefenamic acid, 31%; and furosemide, 31%. Significant increases of 7-15% occurred with diclofenac, flufenamic acid, phenylbutazone, and diphenylhydantoin. Indomethacin, ketoprofen, tolmetin, ethacrynic acid, bumetanide, iopanoate, and ipodate were inactive at the concentrations studied. Addition of 2.0 mmol/L oleic acid had a negligible effect, but 3.5 mmol/L oleic acid inhibited T3 and T4 binding significantly. Other long chain NEFA (addition of 1.5 mmol/L) gave increases in free T4 fraction as follows: arachidonic acid, 26%; linolenic acid, 23%; and linoleic acid, 11%. Stearic and palmitic acids were inactive. The effect of 5 mmol/L oleic acid in serum could be reproduced by addition of 0.5 mmol/L to serum diluted 1:10, indicating that protein binding of NEFA is the major determinant that limits their competitor potency. These findings provide a basis for anticipating which potential inhibitors may cause important changes in serum thyroid hormone binding. The time course of such effects will be influenced by the pharmacokinetics of the inhibitor itself as well as the equilibrium findings described here.
Anti-Inflammatory Agents, Non-Steroidal↗
Changes of circulating thyroxine, triiodothyronine and reverse triiodothyronine after radiographic contrast agents.
Thyroid function was studied for 42 days in 58 patients, 28 of whome had euthyroid goiter, after urography (diatrizoic acid), cholangiography (ioglycamic acid), and cholecystography (Naiopanoate). After urography and cholangiography short-lived increases of the serum thyroxine occurred in a few patients, but the mean thyroxine and triiodothyronine concentration did not change. By contrast, 7 days after oral cholecystography serum thyroxine had risen consistently by 22% with a concomittant rise of the free thyroxine, while triiodothyronine declined by 15%. The thyroxine metabolite 3,3',5'-triiodo-1-thyronine (reverse T3) rose by 50% and serum thyrotropin concentration doubled. After 42 days thryoxine and triiodothyronine had returned to baseline, and none of the 58 patients developed clinical hyperthyroidism. In patients with severe myxoedema kept on a constant replacement dose with 1-thyroxine NA-iopanoate produced similar changes with the exception of the rise of the serum thyroxine. The primary event after Na-iopanoate seems to be a fall of the serum triiodothyronine, which in turn augments thyrotropin and indirectly thyroxine secretion. the marked and sometimes sustained rose of serum thyroxine after cholecystography may lead to the erroneous diagnosis of hyperthyroidism.
Adult↗
Effect of biliary stasis and hepatotoxins on the excretion of iopanoate in the rat.
In rats, hepatic dysfunction was induced with CCl4, SKF 525-A, taurolithocholic acid and alpha-naphthylisothiocyanate and by acute and chronic surgical ligation of the bile duct. Biliary and urinary excretion of 125I-labeled iopanoate was measured after a standard i.v. dose. In the absence of normal biliary excretion, the amount excreted in the urine varied over a wide range (0.25-11.2 percent of the dose), with highest rates of urinary excretion occurring after alpha-naphthylisothiocyanate and chronic stasis. Drug disposition was further determined by tissue analysis of liver and kidney. The results indicate that, for a drug that is normally almost exclusively excreted by the bile, in the presence of hepatic dysfunction the amount excreted by the alternate urinary route depends on the type of the induced hepatic disorder. The intrarenal distribution of 125I-radioactivity is strongly influenced by its plasma concentration rather than just by the rate of excretion in the urine.
Animals↗
Binding of iophenoxate and iopanoate to human serum albumin.
Determination of the binding affinities of 125I-labeled cholecystographic agents to human serum albumin by ultrafiltration techniques is complicated by the appearance of radiochemical impurities resulting from radiolysis of the parent compound. With labeled compounds purified daily by two extractions through chloroform, iophenoxic acid has an extremely high binding affinity. The dissociation constant (K) is 0.013 micronM for iophenoxate, compared to 0.15 micronM for iopanoate, its close analogue. However, at the weaker sites, iophenoxic acid is less strongly bound than iopanoate. The exceptionally high affinity of iophenoxate for a single site of serum albumin appears to underlie its unusual persistence in plasma. Binding in vivo is reversible and not covalent in nature. The choleretic compounds cinchophen and taurocholate have differential effects on the biliary excretion of iophenoxate and iopanoate. This cannot be attributed to selective inhibition of binding to plasma protein.
Crystallization↗
Activation of serum complement by contrast media.
Evidence is presented for the activation of serum complement by contrast media, in vitro and in vivo. Activation as a function of concentration was measured and the increasing order of effectiveness was found to be metrizamide, iothalamate, diatrizoate, acetrizoate, iodipamide and iopanoate. This order is the same as for protein binding and enzyme inhibition. The activation mechanism for iodipamide, and by inference for the other compounds, does not involve gamma-globulin aggregation. Serial daily injections in normal dogs resulted in substantial declines in serum complement over several days. Guinea pigs which were depleted of serum complement with cobra venom factor were found to be no less sensitive to lethal doses of iodipamide than those with normal complement. Implications of these findings are discussed.
Acetrizoic Acid↗
Saturation kinetics of iopanoate in dogs with an intact enterohepatic circulation. Before and after phenobarbital induction.
Capacity-limited elimination of sodium iopanoate and a reproducible apparent transport maximum (Tm) were demonstrated in nonoperated dogs having an intact enterohepatic circulation and normal endogenous bile salt pool. Using a multiple infusion technique, estimation of apparent Tm of iopanoate in the liver was possible without sampling either bile or urine. Values obtained for apparent Tm of iopanoate in dogs with normal bile salt pool were similar to those obtained in studies of dogs with chronic bile fistulas. Use of this technique in 4 dogs demonstrated that pretreatment with phenobarbital significantly increases apparent Tm of iopanoate.
Animals↗
Structure and ligand binding properties of human serum albumin.
1. INTRODUCTION: Serum albumin possesses a unique capability to bind, covalently or reversibly, a great number of various endogenous and exogenous compounds. Several different transport proteins exist in blood plasma but albumin only is able to bind a wide diversity of ligands reversibly with high affinity. The subject of the present thesis is these binding properties. In 1981 the author proposed in a review a model for binding of ligands to serum albumin. In the model, binding of ligands to at least 6 distinct regions was considered. The purpose of the experimental work described here was to test the validity of the model. This was done by performing a large number of competition experiments. From these new data a revised model for ligand binding is presented. 2. STRUCTURE AND CONFORMATIONAL CHANGES OF SERUM ALBUMIN: Human serum albumin consists of 585 amino acids forming a single polypeptide of known sequence. A number of well characterized genetic variants have been reported. The physico-chemical characteristics of the protein are well-established. By contrast, the complete secondary and tertiary structures are not known; information about major structural features only has been obtained. The albumin molecule seems to have an overall ellipsoidal shape (about 140 x 40 A) and to be composed of domains. On the basis of the amino acid sequence, Brown (1977a) proposed a 3-domain model for the protein. Each domain is believed to consist of 6 helices forming a hydrophobic channel with basic and hydrophobic amino acid residues placed at the ends. Experimental data, however, indicate that the domains cannot be identical. Long-chain fatty acid ions are proposed to bind with high affinity within the channels. The ability to fluctuate between isomeric forms in aqueous solution could assist in adapting the albumin molecule to bind ligands with a diverse nature with high affinity. This possibility is discussed on the basis of several physico-chemical techniques including hydrogen-deuterium exchanges. Also the importance of the N-B transition for ligand binding is considered. 3. PRELIMINARY BINDING MODEL OF SERUM ALBUMIN: Single binding of ligands to serum albumin is usually described as high-affinity binding to one or two sites and weaker binding to a larger number of sites. In this chapter, the original binding model for high-affinity binding is elaborated. Region 1 seems to be specific for binding of one, or possibly two, ions of long-chain fatty acids. Region 2 is somewhat less specific and includes binding of octanoate, tryptophan, chlorazepate, thyroxine, p-iodobenzoate and possibly also chloride. Region 3 accommodates bilirubin, Phenol Red, Bromophenol Blue and iopanoate. Region 4 is a special site for strong binding of metal ions such as Cu++ and Ni++. Evidence is presented for placing the primary haemin site in a separate region (no. 5). The existence of additional binding regions, well-suited for high-affinity binding of drugs, is discussed...
Amino Acid Sequence↗
Potential tumor- or organ-imaging agents. 28. Radioiodinated esters of cholesterol and pregnenolone.
Previous studies had shown radioiodinated esters of cholesterol and pregnenolone to accumulate in steroid-secreting tissues of the rat. This was particularly true for radioiodinated iopanoate esters. The present study was undertaken to examine the effect of the iopanoyl amino group on the tissue distribution of these esters. While the tissue distribution profiles for cholesteryl iopanoate and the desamino analog (III) were somewhat comparable, such was not the case for the corresponding esters of pregnenolone. Moreover, this subtle structural change of removing the amino group was observed to affect the in vivo stability of the esters to hydrolysis. This conclusion is in accordance with the observation that the tissue distribution profiles for the free acids I and II are not significantly different from each other. These studies serve to demonstrate that relatively minor modifications of the acyl moiety have a profound effect on both the uptake and distribution of these sterol esters in various tissues.
Animals↗
Selective modification of the active center of renal iodothyronine 5'-deiodinase by iodoacetate.
Pretreatment of renal iodothyronine 5'-deiodinase with sulfhydryl reagents, iodoacetate, iodoacetamide and N-alkylmaleimides, results in irreversible loss of catalytic activity. Iodoacetate and iodoacetamide were the most potent inhibitors, being 100- to 1000-times more potent than N-alkylmaleimides. Iodoacetate and iodoacetamide inactivation followed pseudo-first-order kinetics with maximum inactivation rate constants of 1.56 min-1 and 0.87 min-1, respectively. Thyroxine and 3,3',5'-triiodothyronine and the competitive inhibitor iopanoate, protected the enzyme against iodoacetate inhibition. Protection by 3,3',5'-triiodothyronine was competitive with iodoacetate with a dissociation constant (Kd) of 113 nM; in close agreement with the Km for rT3 of 190 nM determined under similar reaction conditions. [3H]Carboxymethylation of renal membranes in the absence and presence of 3,3',5'-triiodothyronine showed specific incorporation of iodo[3H]acetate into substrate-protected sites of 35-40% of total when non-essential residues were first blocked with excess unlabeled iodoacetate. ' Protectable ' [3H]acetate incorporation followed pseudo-first-order kinetics and the rate constant for incorporation was identical to the rate constant for inactivation. These results indicate that iodoacetate fulfills the minimum criteria for an active-site-directed reagent for renal 5'-deiodinase and that a sulfhydryl group is in close proximity to the iodothyronine-binding site.
Animals↗