Transport of 99mTc-MAG3 via rat renal organic anion transporter 1.

UNLABELLED: Recently, complementary DNA (cDNA) encoding a p-aminohippurate (PAH) transporter designated rat organic anion transporter 1 (OAT1) was isolated. OAT1, a multispecific organic anion transporter at the basolateral membrane, is exclusively expressed in the middle segment of the proximal tubule in the rat kidney. It has been proposed that OAT1 is indirectly involved in PAH uptake via the Na(+) dicarboxylate cotransporter. In this study, in molecular biologic experiments using OAT1-expressing Xenopus laevis oocytes, we obtained evidence that (99m)Tc-mercaptoacetylglycylglycylglycine (MAG3) is transported via OAT1. METHODS: Capped OAT1 complementary RNA (cRNA) was synthesized from library plasmid cDNA linearized with BamHI using in vitro transcription. Defolliculated oocytes were injected with 10 ng of OAT1 cRNA. Two to 3 d after injection, uptake of (99m)Tc-MAG3 was measured using ND96 solution containing 18.5 kBq of (99m)Tc-MAG3. Before the uptake experiments, OAT1-expressing oocytes were preincubated for 2 h with 1 mmol/L glutarate (a dicarboxylate), to generate an outwardly directed glutarate gradient. Then, after incubation for 60 min at room temperature, radioactivity of oocytes was determined. For the inhibition experiments, uptake was assessed in the absence or presence of inhibitor: 2 mmol/L of PAH, o-iodohippurate (OIH), probenecid, 3,5-diiodo-4-pyridone-N-acetate (iodopyracet), furosemide, ethacrynic acid, glucoheptonate, maleic acid, L-Tyr, or tetraethylammonium (TEA) or 0.1 mmol/L of 2,4-dinitrophenol (DNP). RESULTS: Na(+) had a significant effect on (99m)Tc-MAG3 uptake (P < 0.05). Accumulated glutarate stimulated simultaneous (99m)Tc-MAG3 uptake and glutarate excretion (P < 0.001). The following compounds significantly inhibited (99m)Tc-MAG3 uptake: PAH, 8.5% +/- 16.2% of (99m)Tc-MAG3 uptake in the absence of an inhibitor; OIH, 26.4% +/- 21.7%; probenecid, 29.1% +/- 12.4%; iodopyracet, 15.8% +/- 7.9%; furosemide, 30.5% +/- 15.7%; ethacrynic acid, 21.6% +/- 10.6%; glucoheptonate, 35.6% +/- 22.6%; and maleic acid, 60.1% +/- 18.7%. (99m)Tc-MAG3 accumulation in Xenopus laevis oocytes was not significantly inhibited by TEA, L-Tyr, or DNP. CONCLUSION: The following substances had a cis-inhibitory effect on (99m)Tc-MAG3 transport: PAH, OIH, probenecid, iodopyracet, furosemide, ethacrynic acid, and glucoheptonate. Glutarate had a trans-stimulative effect on (99m)Tc-MAG3 transport. (99m)Tc-MAG3 acts as a substrate of OAT1, an organic anion/dicarboxylate exchanger.

Effect of iodopyracet on renal excretion of sulfamethizole in rabbits.

To predict quantitatively drug interaction kinetics from the single-drug clearance studies, we examined the effect of iodopyracet (IOD) on sulfamethizole (SMZ) excretion in rabbits. Even though the decline of systemic IOD plasma concentration was linear, the renal clearance of SMZ decreased significantly in the presence of IOD. The results could be described by a perfusion model incorporated with the competitive inhibition for tubular secretion. For IOD with a high extraction ratio, it was suggested that a heavy load of the drug was supplied to the sites of secretion and caused the saturation of transport systems, even though the renal excretion kinetics were apparently linear in respect to the systemic circulation. These facts indicated that a linear relationship between the concentrations in the systemic circulation and at the sites of tubular secretion can not always be presumed. Consequently, SMZ-IOD interaction study stressed the importance of the drug concentrations at the sites of interaction for quantitative elucidation of drug-drug interactions.

[Tubular secretion of cardiotrast in the progeny of rats receiving it throughout pregnancy]. / Kan al'tsevaia sekretsiia kardiotrasta u potomstva krys, poluchavshikh ego na protiazhenii beremennosti.

Administration of cardiotrast (50-80 mg twice a day subcutaneously) during pregnancy was shown to induce a significant suppression of tubular secretion of the xenobiotic in the offspring. When cardiotrast was given only in the postnatal period, tolerance failed to develop.

[Characteristics of the granules formed in nucleated erythrocytes as affected by cardiotrast]. / Kharakteristika granul, obrazuiushchikhsia v iadernykh éritrotsitakh pod vliianiem kardiotrasta.

Numerous granules are formed in frog erythrocytes under the influence of cardiotrast (C) (diethanolamine-3,5-diiodo-4-pyridone-1-acetic acid). However, as revealed by cytospectrophotometric investigation and X-ray microanalysis, no C was accumulated in these granules. It is known that C can dissociate into diethanolamine and 3,5-diiodo-4-pyridone-1-acetic acid. It was assumed that under the influence of C granule formation may occur at the expense of an uncharged diethanolamine form penetrating into lysosome-like structures to be accumulated by protonation process. Diethanolamine was found to provoke granule formation in frog erythrocytes. It is impossible to reveal substance in granules because it is colourless and has no ultraviolet absorbtion band. Under the influence of some inhibitors of energy metabolism on granule formation and the granules formed, their inhibitory effect is exerted on the process of granule formation. In granules isolated by differential centrifugation activity of some marker lysosomal enzymes was found which enabled us to attribute these granules to lysosome-like structures.

[Effect of contrast media on the structure and function of hepatocyte plasma membranes]. / Vliianie kontrastnykh sredstv na strukturu i funktsiiu plazmaticheskikh membran gepatotsitov.

The cholecystographic radiopaque agents, adipiodon and endographin, unlike the urographic contrast agents, triombrin and iodamide, decrease the fluorescence intensity of hydrophobic probes 1-anilinonaphthalene-8-sulfonate and 4-dimethylaminochalcone in plasmic membranes (PM) of rat hepatocytes primarily at the expense of the lowering of the constant of probe association with the membranes. The similar but less marked effects were discovered in experiments with lecithin lyposomal preparations. As regards the intensity of action, cardiotrast and triotrast an intermediate position between the two groups of radiographic contrast agents. Adipiodon and endographin induce an inhibition of membranous Mg+2 (Na+, K+) ATPase, which correlates with their effect on the structure of the hepatocyte PM. The data obtained allow a conclusion that, unlike the urographic agents, the cholecystographic radiopaque agents are bound to the definite areas of the hepatocytic PM and provoke alterations in the activity of membranous APTase because of the conformational rearrangements of the membranes.

The transport of para-aminohippuric acid by the ciliary body and by the iris of the primate eye.

Para-aminohippuric acid (PAH) accumulates against a concentration gradient in the ciliary body and independently in the iris of the rhesus monkey eye. This accumulation is inhibited by incubation of 0 degrees C and shows saturation kinetics in both tissues. Cyanide, ouabain, dinitrophenol, iodopyracet, and probenecid effectively depress PAH uptake in both tissues, but anaerobic incubation conditions have little effect on uptake in either tissue. The washout of preaccumulated PAH occurs 2.5 times faster from the iris than from the ciliary body. The effects on washout of 10(-4)M PAH, 0 degrees C, and 10(-5)M dinitrophenol are consistent with washout occurring by a diffusional mechanism in both tissues, with some reaccumulation occurring in the ciliary body only. In addition, nonsaturable uptake of PAH, studied in both tissues under high PAH concentrations, also occurs significantly faster in the iris than in the ciliary body. The kinetic analysis of active PAH uptake in both tissues is discussed in terms of initial uptake and in terms of a steady-state model. This steady-state model compensates for some technical problems in applying in vitro incubation techniques to primate tissues and also includes a correction for the additional exchange processes that affect the two tissues differently. Results of the kinetic analysis suggest that, at least to an order of magnitude, iris uptake is significant with respect to ciliary body uptake.

[Effect of contrast media on the rate of oxidation of NADP.H and NAD.H by rat liver microsomes]. / Issledovanie deistviia rentgenokontrastnykh veshchestv na skorost' okisleniia NADF.H i NAD.H mikrosomami pecheni krys.

The effect of roentgen-contrast media on the activity of the NADP'N and NAD'N-dependent electron-transport chains of the rats liver microsomes was studied. Bilignost, cardiotrast, triiotrast and triombrin are shown to lower the rate of the NADP'N oxidation by the rats' liver microsomes and have no effect (except for triiotrast) upon the rate of the NAD'N oxidation. It is presumed that the relative resistance of the NAD'N-specific flavoproteid is due to the presence of a hydrophobic layer impervious to the polar molecules of the contrast media.

[Study of interaction between contrast media and human serum albumin by the fluorescence method]. / Issledovanie vzaimodeistviia rentgenokontrastnykh vesh chestv s syvorotochnym al'buminom cheloveka metodom fliuorestsentsii.

Structural changes in the human serumal albumin under the effect of roentgen-contrast media, viz. bilignost, triiotrast, endografine, iodamide, triombrine and cardiotrast, were investigated by the method of fluorescence. The complex-formation of albumin with triiodotrast, bilignost and endografine was shown to call forth a short-wave shift of the fluorescence peak by approximately 20 nm. The binding section for these substances is characterized by an association constant equalling 1.2-10(5) M-1. The authors presume that triiodotrast, bilignost and endografine cause changes in the microstructure of the aqueo-protein layer in the area of the tryptophan residue localization. As to triombine, iodamide and cardiotrast fluorescence failed to disclose their combination with the human serumal albumin.

Pyrazinoate excretion in the chimpanzee. Relation to urate disposition and the actions of uricosuric drugs.

These experiments were designed to define the renal disposition of pyrazinoic acid in a nonhuman primate that is phylogenetically close to man and to relate this to the effects of pyrazinoate on urate excretion. The renal clearance of pyrazinoate was almost always greater than the simultaneous glomerular filtration rate at plasma concentrations ranging from 1.9 to 960 mug/ml. Some inhibitors of tubular secretion, probenecid, MK-282 (an experimental, potent uricosuric drug), p-aminohippurate, iodopyracet, sulfinpyrazone, and mersalyl, reduced clearances of pyrazinoate to values far below filtration rate. Chlorothiazide, allopurinol, and salicylate did not. The clearance of pyrazinoate was not influenced by changes in urine flow. It is concluded that pyrazinoate is actively secreted and actively reabsorbed. Pyrazinoate had a dual effect on urate excretion. At concentrations in plasma less than 10 mug/ml there was a concentration related fall in urate/inulin clearance ratio, reaching values of 10-20% of control. Over the range of 10-100 mug/ml in plasma, the clearance of urate remained maximally depressed. At higher concentrations of pyrazinoate there was a concentration related increase in urate/inulin clearance ratio such that at pyrazinoate levels above 600 mug/ml a definite uricosuric response was obtained. Prior administration of pyrazinoate to give plasma levels of 20-140 mug/ml completely or almost completely prevented uricosuric responses to probenecid, PAH, chlorothiazide, and sulfinpyrazone. Iodopyracet, mersalyl, salicylate and N-acetyl-4-dibutylsulfamoyl-3-trifluoromethylbenzenesulfonamide (MK-282) retained significant uricosuric action, but the activities were probably less than normal. The results are consistent with a model of urate transport involving high rates of bidirectional transtubular flux.