We investigated immunohistochemical localization of V2 vasopressin receptor along the nephron using a specific polyclonal antibody. Staining was observed in some of thick ascending limbs and all of principal and inner medullary collecting duct (IMCD) cells. Not only basolateral but also luminal membrane was stained in collecting ducts, especially in terminal IMCD (tIMCD).To learn the functional role of luminal V2 receptor in tIMCD, we studied the luminal effects of arginine vasopressin (AVP) on osmotic water permeability (Pf), urea permeability (Pu), and cAMP accumulation using isolated perfused rat tIMCD. In the absence of bath AVP, luminal AVP caused a small increase in cAMP accumulation, Pf and Pu, confirming the presence of V2 receptor in the lumen of tIMCD. In contrast, luminal AVP inhibited Pf and Pu by 30-65% in the presence of bath AVP by decreasing cAMP accumulation via Vla or oxytocin receptors and by an unknown mechanism via V2 receptors in the luminal membrane of tIMCD.These data show that V2 receptors are localized not only in the basolateral membrane but also in the luminal membrane of the distal nephron. Luminal AVP acts as a negative feedback system upon the basolateral action of AVP in tIMCD. (J. Clin. Invest. 1995. 96:1768-1778

This study was designed to examine the effects of oral adsorbent AST-120 on the progression of CRF in patients on strict LPD. Thirteen patients with CRF (serum creatinine: 1.8-8.2 mg/ dl) that had been kept on LPD (0.4-0.7 g/kg/day) were enrolled in this study. After LPD alone for 5-24 months, AST-120 (3-6 g/day) was administered concurrently with the LPD for an additional 5-13 months. In 9 of the 13 patients, the slopes of reciprocal creatinine (Cr) vs. time plot linearly declined before AST-120 treatment. After treatment, the slopes of these patients lessened from -0.01 ± 0.001 to -0.003 ± 0.001 dl/mg/month (p < 0.01). Because reciprocal Cr did not decline linearly with time before AST-120 treatment in the remaining 4 patients, the slopes of reciprocal Cr could not be compared before and after treatment with AST-120. Seven of the 9 patients had sufficient creatinine clearance (C_cr) data after treatment with AST-120. The decline of C_cr decreased from -0.59 ± 0.13 to -0.12 ± 0.12 ml/min/ month in these patients. This study has clearly demonstrated that AST-120 compounds the effects of well-controlled LPD on retarding the progression of CRF. AST-120 may remove some uremic metabolite(s) which promote the progression of CRF.

We identified and quantified indoxyl-β-D-glucuronide in uremic serum and urine to determine the metabolism of indoles including indoxyl sulfate in uremic patients. Serum levels of indoxyl-β-D-glucuronide were markedly increased in undialyzed uremic patients, in patients on hemodialysis, and in patients on continuous ambulatory peritoneal dialysis. Urinary excretion of indoxyl-β-D-glucuronide was also increased in undialyzed uremic patients. Urinary indoxyl-β-D-glucuronide was significantly correlated with serum indoxyl sulfate, indicating that a high serum level of indoxyl sulfate leads to the enhanced synthesis of indoxyl-β-D-glucuronide. Oral sorbent (AST-120) administration markedly decreased the serum and urine levels of indoxyl-β-D-glucuronide as well as indoxyl sulfate in the undialyzed uremic patients. Serum indoxyl-β-D-glucuronide could be efficiently removed by hemodialysis despite its high protein-binding ratio of about 50%. In conclusion, the serum level of indoxyl-β-D-glucuronide increases in uremic patients due to renal insufficiency and its increased production. The production of indoxyl-β-D-glucuronide can be suppressed by oral sorbent treatment, and serum indoxyl-β-D-glucuronide can be efficiently removed by hemodialysis.

We investigated the effects of endothelins on receptor-mediated cyclic nucleotide metabolism in rat glomerulus, inner medullary collecting duct (IMCD), and also in cultured rat glomerular mesangial cells. Endothelin (ET)-3 dose-dependently stimulated cGMP accumulation in glomerulus, which was higher than that of ET-1 or ET-2. ETB receptor agonist IRL 1620 produced cGMP in a dose-dependent manner, mimicking the effect of ET-3. ETA receptor antagonist BQ123-Na did not inhibit ET-3-or IRL 1620-stimulated cGMP generation. NG-monomethyl-L-arginine (L-NMMA) significantly inhibited ET-3-or IRL 1620-induced cGMP production, suggesting that ET-3-or IRL 1620-stimulated cGMP generation was mediated through nitric oxide (NO). Intracellular Ca chelator BAPTA /AM and calmodulin antagonist W-7, but not Ca channel blocker nicardipine, significantly inhibited ET-3-or IRL 1620-induced cGMP generation. In cultured rat mesangial cells, ET-3 stimulated cGMP generation through NO in the presence of fetal calf serum, which was not inhibited by addition of BQ123-Na. In IMCD, ET-3 had no stimulative effect on cGMP generation. We conclude that ET-3 stimulates NO-induced cGMP generation through ETB receptor in glomerulus. This effect seems to be mediated through intracellular Ca/calmodulin, but not through Ca influx via L-type Ca channel. Mesangial cells can be a source of NO coupled to ETB receptor activation in glomerulus. From these results, mesangial ETB receptor may work to counteract the vasoconstrictive effect of endothelin caused via ETA receptor in glomerulus. (J.

We recently demonstrated that indoxyl sulfate is a stimulating factor for the progression of chronic renal failure (CRF). In this study we determined whether the urine or serum levels of indoxyl sulfate are related to the progression rate of CRF in undialyzed uremic patients. Fifty-five CRF patients with a serum creatinine of >2 mg/dl who had not been treated with an oral sorbent (AST-120) were randomly enrolled in the study. We measured the serum and urine levels of indoxyl sulfate, and estimated the recent progression rate of CRF as the slope of the reciprocal serum creatinine versus time (1/S-Cr-time) plot. The mean urinary amount of indoxyl sulfate in the patients was 60 mg/day. Those with indoxyl sulfate urine levels of >60 mg/day had a significantly faster progression rate of CRF than those with <60 mg/day. Especially, those patients with indoxyl sulfate urine levels of >90 mg/day had the highest CRF progression rate and those with indoxyl sulfate urine levels of <30 mg/day had the slowest CRF progression rate. Urinary indoxyl sulfate had a significantly negative correlation with the slope of the 1/S-Cr-time plot. However, the serum level of indoxyl sulfate or the ratio of serum indoxyl sulfate to creatinine was not significantly correlated with the slope of the 1/S-Cr-time plot. In conclusion, high urine levels of indoxyl sulfate are related with a rapid progression of CRF in undialyzed uremic patients. Thus, urinary indoxyl sulfate is one of the clinical factors that affect CRF progression.