Identification of N-monoacetylcystine in uraemic plasma

Effect of experimental renal failure on the pharmacokinetics of losartan in rats

The purpose of this investigation was to determine whether the pharmacokinetics of the angiotensin II receptor antagonist losartan is altered in renal failure. Male Wistar rats were pretreated with uranyl nitrate or subjected to bilateral ureteral ligation to produce acute renal failure (ARF). Saline-injected and sham-operated rats, respectively, served as controls. Uranyl nitrate-treated rats showed significantly higher serum concentrations of losartan after oral administration and the area under the serum concentration-time curve (AUC(0-24)) of losartan increased about 3-fold compared to control rats. The systemic clearance of losartan significantly decreased from 410 +/- 254ml/h/kg in control to 177 +/- 112ml/h/kg in uranyl nitrate-treated rats. In order to investigate the mechanisms of reduced clearance of losartan associated with ARF, a hepatic microsome fraction was prepared from normal and ARF rats. No significant difference was found in the metabolism of losartan by hepatic microsomes prepared from ARF and control rats. In addition, the metabolic activity of microsomes was examined in the presence of uremic rat serum. The unbound clearance of losartan and the unbound clearance associated with the formation of EXP3174 in the presence of uremic serum were significantly lower than those in the presence of control serum. Furthermore, the metabolism of losartan was inhibited by indoxyl sulfate, a uremic toxin, in an uncompetitive manner. These results suggest that ARF is associated with reduced clearance of losartan due to the inhibition of hepatic metabolism by accumulated uremic toxin(s).

beta-Sulfopyruvate: chemical and enzymatic syntheses and enzymatic assay

beta-Sulfopyruvic acid (2-carboxy-2-oxoethanesulfonic acid) is prepared in greater than 90% yield by reaction of bromopyruvic acid with sodium sulfite. beta-[35S]Sulfopyruvate is prepared by transamination between [35S]cysteinesulfonate (cysteate) and alpha-ketoglutarate using mitochondrial aspartate aminotransferase isolated from rat liver. Following either chemical or enzymatic synthesis, the crude reaction product is conveniently purified by chromatography on Dowex 1; beta-sulfopyruvate is isolated as the stable, water-soluble dilithium salt. beta-Sulfopyruvate is shown to be an alternative substrate of mitochondrial malate dehydrogenase; in the presence of 0.25 mM NADH, beta-sulfopyruvate is reduced with an apparent Km of 6.3 mM and a Vmax equal to about 40% of that observed with oxaloacetate. This finding forms the basis of a convenient spectrophotometric assay of beta-sulfopyruvate.