The effect of acute renal failure (ARF) induced by ischemia/reperfusion (I/R) of rat kidney on the expression of organic anion transporters (OATs) was examined. The level of serum indoxyl sulfate (IS), a uremic toxin and substrate of OATs in renal tubules, shows a marked increase with the progression of ARF. However, this increase was significantly attenuated by ingestion of cobalt. The level of mRNA and protein of both rOAT1 and rOAT3 were markedly depressed in the ischemic kidney. The uptake of p-aminohippuric acid (PAH) and estrone sulfate (ES) by renal slices of ischemic rats was significantly reduced compared to control rats. Renal slices taken from ischemic rats treated with cobalt displayed significantly elevated levels of ES uptake. Cobalt intake did not affect PAH uptake, indicating the functional restoration of rOAT3 but not rOAT1. The expression of Na(+)/K(+)-ATPase was markedly depressed in the ischemic kidney, suggesting that the inward Na(+) gradient in renal tubular cells had collapsed, thereby reducing the outward gradient of alpha-ketoglutarate, a driving force of both rOATs. The decreased expression of Na(+)/K(+)-ATPase was significantly restored by cobalt treatment. Our results suggest that the downregulation of renal rOAT1 and rOAT3 could be responsible for the increase in serum IS level of ischemic rats. Cobalt treatment has a significant protective effect on ischemia-induced ARF, being accompanied by the restoration of rOAT3 and/or Na(+)/K(+)-ATPase function.

A. Vasopressin regulates the renin-angiotensin-aldosterone system via V1a receptors in macula densa cells.

ABSTRACT:In the proximal tubules of rat (r) kidney, the polyspecific organic cation transporters (OCTs), rOCT1 and rOCT2, mediate the basolateral uptake of various organic cations, including many drugs, toxins, and endogenous compounds, and the apical type of H ؉ / organic cation antiporter, rat multidrug and toxin extrusion 1 (rMATE1), mediate the efflux of organic cations. Renal clearances of H 2 receptor antagonists, including famotidine, were reported to be decreased in patients with kidney disease. Therefore, acute kidney injury (AKI) could influence renal excretion and disposition of organic cations accompanied by the regulation of organic cation transporters. The aim of this study was to investigate the pharmacokinetic alteration of cationic drugs and the expression of tubular organic cation transporters, rOCT1, rOCT2, and rMATE1, in ischemia/reperfusion (I/R)-induced AKI rats. I/R-induced AKI increased the plasma concentration of i.v. administrated famotidine, a substrate for rOCT1 and rOCT2, or tetraethylammonium (TEA), a substrate for rOCT1, rOCT2, and rMATE1. The areas under the plasma concentration curves for famotidine and TEA were 2-and 6-fold higher in I/R rats than in sham-operated rats, respectively. The accumulation of TEA into renal slices was significantly decreased, suggesting that organic cation transport activity at the basolateral membranes was reduced in I/R rat kidney. The protein expressions of basolateral rOCT2 and luminal rMATE1 were down-regulated in I/R rat kidneys. These data suggest that the urinary secretion of cationic drugs via epithelial organic cation transporters is decreased in AKI.

An increase in the IS level and the associated disturbance to the circadian rhythm are involved in the renal and CNS toxicities in CDDP-treatment.

2 system plays a key role in urine concentration in dehydration. In contrast to the upregulation of aquaporin 2, the downregulation of the vasopressin V2 receptor in dehydration is known. We investigated the mechanisms of this downregulation in dehydration using reverse transcription-competitive polymerase chain reaction (RT-competitive PCR) and Western blot analysis. The incubation of microdissected inner medullary collecting ducts (IMCDs) in a hypertonic medium or with vasopressin stimulated V2 receptor mRNA and protein expression, showing that dehydration-induced hyperosmolality in renal medulla and increased plasma arginine vasopressin (AVP) concentration should upregulate V2 receptor. The presence of inhibitory factors on the V2 receptor in dehydration was suggested. Prostaglandin E2 (PGE2) is known to inhibit AVP-induced cAMP production and to increase production in dehydration. PGE 2 slightly stimulated V2 receptor mRNA expression in IMCD in vitro. However, PGE 2 inhibited V2 receptor mRNA expression in IMCD in the presence of 10 Ϫ9 M vasopressin. The blockade of PGE2 synthesis by indomethacin in dehydrated rats increased V2 receptor protein expression after 24 -48 h with an early increase in V2 receptor mRNA expression. In summary, these data suggest that increased production of PGE 2 in renal medulla plays a key role in the downregulation of V2 receptor in dehydration. V2 receptor; aquaporin 2; prostaglandin E2; inner medullary collecting duct THE MAIN ROLE of the kidney is to maintain body fluid homeostasis. The kidney is a target site of many hormones such as arginine vasopressin (AVP), endothelin, atrial natriuretic peptide (ANP), parathyroid hormone (PTH), glucagon, and aldosterone. AVP plays a key role in urine concentration in the case of dehydration (18). AVP has two types of receptors in the kidney, V1a and V2 receptors. V1a receptors mediate the vasopressor effects of AVP and are localized in renal vessels and in the thick ascending limbs and the collecting ducts (26,28,34). In contrast, V2 receptors mediate the antidiuretic action of AVP and are localized in the thick ascending limbs and the collecting ducts (9,16,25,34). In the collecting ducts, the V2 receptor is located in the basolateral membrane of principal cells, while V1a receptor is mainly in the luminal membrane of both principal and intercalated cells (9,25,33). Urine concentration is caused by the binding of AVP to the V2 receptor and by the subsequent activation of aquaporin-2 (AQP2) (13,14,19,23). The V2 receptor acts as Gs and stimulates adenylate cyclase. Nephrogenic diabetes insipidus is caused by an abnormality in the V2 receptor or AQP2 (20). AQP2 is present in the luminal membrane and intracellular vesicles of principal cells (22). The V1a receptor activates Gq/11 and subsequently phosphoinositide turnover (1).In dehydration, trafficking of AQP2 in the intracellular vesicles to the apical membrane occurs as a short-term regulation (23). In long-term regulation, the expression of AQP2 is stimulated in chronic dehydration (35...

These results suggest that hypomagnesemia could cause dehydration and up-regulation of rOCT2, enhancing renal accumulation of CDDP and the deterioration of AKI.

In vitro-in vivo extrapolation (IVIVE) of renal excretory clearance (CL R ) using the physiologically based kidney models can provide mechanistic insight into the interplay of multiple processes occurring in the renal tubule; however, the ability of these models to capture quantitatively the impact of perturbed conditions (e.g., urine flow, urine pH changes) on CL R has not been fully evaluated. In this work, we aimed to assess the predictability of the effect of urine flow and urine pH on CL R and tubular drug concentrations (selected examples). Passive diffusion clearance across the nephron tubule membrane was scaled from in vitro human epithelial cell line Caco-2 permeability data by nephron tubular surface area to predict the fraction reabsorbed and the CL R of caffeine, chloramphenicol, creatinine, dextroamphetamine, nicotine, sulfamethoxazole, and theophylline. CL R values predicted using mechanistic kidney model at a urinary pH of 6.2 and 7.4 resulted in prediction bias of 2.87-and 3.62-fold, respectively. Model simulations captured urine flow-dependent CL R , albeit with minor underprediction of the observed magnitude of change. The relationship between drug solubility, urine flow, and urine pH, illustrated in simulated intratubular concentrations of acyclovir and sulfamethoxazole, agreed with clinical data on tubular precipitation and crystal-induced acute kidney injury. This study represents the first systematic evaluation of the ability of the mechanistic kidney model to capture the impact of urine flow and urine pH on CL R and drug tubular concentrations with the aim of facilitating refinement of IVIVE-based mechanistic prediction of renal excretion.

Cisplatin-induced AKI causes down-regulation of renal organic ion transporters accompanied by accumulation of serum and renal IS. IS could be involved in the mechanism of down-regulation of rOAT1, rOAT3 and rMATE1 under cisplatin-induced AKI.