scholarly journals The role of tubular reabsorption in the renal excretion of bile acids

1977 ◽  
Vol 166 (1) ◽  
pp. 65-73 ◽  
Author(s):  
S Barnes ◽  
J L Gollan ◽  
B H Billing
Keyword(s):  
Bile Acids ◽  
Renal Excretion ◽  
Rat Kidney ◽  
Tubular Secretion ◽  
Tubular Reabsorption ◽  
Free Medium ◽  
Proximal Tubular ◽  
Protein Free Medium ◽  
Conjugated Bilirubin

1. The renal excretion of bile acids was studied in an isolated rat kidney preparation perfused with a protein-free medium. 2. Tubular reabsorption exceeded 95% for both non-sulphated and sulphated bile acids at filtered loads of less than 30 nmol/min. 3. At low filtered loads the reabsorption of taurocholate and taurochenodeoxycholate was almost complete. Efficient reabsorption of taurochenodeoxycholate was maintained over a wider range of filtered loads than for taurocholate. These observations suggest that active transport may occur. 4. At high filtered loads saturation of reabsorption of taurocholate and taurochenodeoxycholate did not occur, which indicates that passive diffusion is involved in reabsorption. 5. Active proximal-tubular secretion of bile acids was not demonstrated in competition experiments with p-aminohippurate. 6. The fractional reabsorption of taurocholate, chenodeoxycholate 3,7-disulphate and chenodeoxycholate 7-monosulphate was decreased by the addition of taurochenodeoxycholate to the perfusate, so that their renal excretion was enhanced. This interaction between the bile acids for reabsorption may explain the different composition of bile acids in urine compared with that in plasma in cholestasis in man. 7. Conjugated bilirubin decreased the fractional reabsorption of both taurocholate and taurochenodeoxycholate at low filtered loads (less than 30 nmol/min) but not at high filtered loads (400 nmol/min).

Role of luminal hydrostatic pressure in proximal tubular fluid reabsorption in the rat

1975 ◽  
Vol 229 (3) ◽  
pp. 813-819 ◽  
Author(s):  
A Grandchamp ◽  
Scherrer ◽  
D Scholer ◽  
J Bornand
Keyword(s):  
Hydrostatic Pressure ◽  
Proximal Tubule ◽  
Pressure Difference ◽  
Unit Area ◽  
Rat Kidney ◽  
Fluid Reabsorption ◽  
Proximal Tubular ◽  
Tubular Fluid Reabsorption ◽  
Selective Change

The effect of small changes in intraluminal hydrostatic pressure (P) on the tubular radius (r) and the net fluid reabsorption per unit of surface area of the tubular wall (Js) has been studied in the proximal tubule of the rat kidney. The split-drop method was used to simultaneously determine Js and r. Two standardized split-drop techniques A and B allow selective change in P. P was 31.6 +/- 1.3 mmHg in technique A and 15.5 +/- 1.5 in technique B. The pressure difference significantly affected the tubular radius; r was 21.9 +/- 0.4 and 18.6 +/- 0.5 mum in the split drop A and B, respectively. In contrast, net transepithelial fluid reabsorption Js was unchanged. Js amounted to 2.72 +/- 0.20, and 2.78 +/- 0.33 10(-5) cm3 cm-2 s-1 in split drop A and B. The absence of variations in Js could result from two opposite effects of pressure. P might enhance Js by increased ultrafiltration. However, the rise in r might decrease the density of the intraepithelial transport paths per unit area of tubular wall and therefore might decrease Js.

Tubular Reabsorption of Bile Acids by the Isolated Rat Kidney

1976 ◽  
Vol 51 (3) ◽  
pp. 14P-15P
Author(s):  
S. Barnes ◽  
J. Gollan ◽  
Barbara H. Billing
Keyword(s):  
Bile Acids ◽  
Rat Kidney ◽  
Tubular Reabsorption ◽  
Isolated Rat Kidney ◽  
Isolated Rat

The role of angiotensin converting enzyme 2 in the generation of angiotensin 1–7 by rat proximal tubules

2005 ◽  
Vol 288 (2) ◽  
pp. F353-F362 ◽  
Author(s):  
Ningjun Li ◽  
Joseph Zimpelmann ◽  
Keding Cheng ◽  
John A. Wilkins ◽  
Kevin D. Burns
Keyword(s):  
Rat Kidney ◽  
Biologically Active ◽  
Relative Distribution ◽  
Ang Ii ◽  
Converting Enzyme ◽  
Angiotensin Converting Enzyme 2 ◽  
Nephron Segments ◽  
Luminal Perfusion ◽  
Proximal Tubular

ANG converting enzyme (ACE) 2 (ACE2) is a homologue of ACE, which is not blocked by conventional ACE inhibitors. ACE2 converts ANG 1–10 (ANG I) to ANG 1–9, which can be hydrolyzed by ACE to form the biologically active peptide ANG 1–7. ACE2 is expressed in the kidney, but its precise intrarenal localization is unclear, and the role of intrarenal ACE2 in the production of ANG 1–7 is unknown. The present studies determined the relative distribution of ACE2 in the rat kidney and defined its role in the generation of ANG 1–7 in proximal tubule. In microdissected rat nephron segments, semiquantitative RT-PCR revealed that ACE2 mRNA was widely expressed, with relatively high levels in proximal straight tubule (PST). Immunohistochemistry demonstrated ACE2 protein in tubular segments, glomeruli, and endothelial cells. Utilizing mass spectrometry, incubation of isolated PSTs with ANG I (10−6 M) led to generation of ANG 1–7 (sensitivity of detection > 1 × 10−9 M), accompanied by the formation of ANG 1–8 (ANG II) and ANG 1–9. The ACE2 inhibitor DX600 completely blocked ANG I-mediated generation of ANG 1–7. Incubation of PSTs with ANG 1–9 also led to generation of ANG 1–7, an effect blocked by the ACE inhibitor captopril or enalaprilat, but not by DX600. Incubation of PSTs with ANG II or luminal perfusion of ANG II did not result in detection of ANG 1–7. The results indicate that ACE2 is widely expressed in rat nephron segments and contributes to the production of ANG 1–7 from ANG I in PST. ANG II may not be a major substrate for ACE2 in isolated PST. The data suggest that ACE2-mediated production of ANG 1–7 represents an important component of the proximal tubular renin-ANG system.

Retention of fetuin-A in renal tubular lumen protects the kidney from nephrocalcinosis in rats

2013 ◽  
Vol 304 (6) ◽  
pp. F751-F760 ◽  
Author(s):  
Isao Matsui ◽  
Takayuki Hamano ◽  
Satoshi Mikami ◽  
Kazunori Inoue ◽  
Akihiro Shimomura ◽  
...  
Keyword(s):  
Rat Kidney ◽  
Proximal Tubules ◽  
Fetuin A ◽  
Receptor Associated Protein ◽  
Tubular Lumen ◽  
Proximal Tubular ◽  
Normal Rat ◽  
Natural Inhibitor ◽  
Renal Tubular

The serum glycoprotein fetuin-A is an important inhibitor of extraosseous calcification. The importance of fetuin-A has been confirmed in fetuin-A null mice, which develop widespread extraosseous calcification including the kidney. However, the mechanism how fetuin-A protects kidneys from nephrocalcinosis remains uncertain. Here, we demonstrate that intratubular fetuin-A plays a role in the prevention of nephrocalcinosis in the proximal tubules. Although normal rat kidney did not express mRNA for fetuin-A, we found punctate immunohistochemical staining of fetuin-A mainly in the S1 segment of the proximal tubules. The staining pattern suggested that fetuin-A passed through the slit diaphragm, traveled in the proximal tubular lumen, and was introduced into proximal tubular cells by megalin-mediated endocytosis. To test this hypothesis, we inhibited the function of megalin by intravenous injection of histidine-tagged soluble receptor-associated protein (His-sRAP), a megalin inhibitor. His-sRAP injection diminished fetuin-A staining in the proximal tubules and led to urinary excretion of fetuin-A. We further analyzed the role of fetuin-A in nephrocalcinosis. Continuous injection of parathyroid hormone (PTH) 1–34 induced nephrocalcinosis mainly in the proximal tubules in rats. His-sRAP retained fetuin-A in renal tubular lumen and thereby protected the kidneys of PTH-treated rats from calcification. Our findings suggest that tubular luminal fetuin-A works as a natural inhibitor against calcification in the proximal tubules under PTH-loaded condition.

scholarly journals The Role of NF-kB in the Downregulation of Organic Cation Transporter 2 Expression and Renal Cation Secretion in Kidney Disease

2022 ◽  
Vol 8 ◽  
Author(s):  
Chao Han ◽  
Juan Zheng ◽  
Fengyi Wang ◽  
Qingyang Lu ◽  
Qingfa Chen ◽  
...  
Keyword(s):  
Kidney Disease ◽  
Organic Cation ◽  
Rat Kidney ◽  
Basolateral Membrane ◽  
Kidney Injury ◽  
Organic Cation Transporter ◽  
Tubular Secretion ◽  
Gene Reporter Assay ◽  
Organic Cation Transporter 2

Organic cation transporter 2 (OCT2), encoded by the SLC22A2 gene, is the main cation transporter on the basolateral membrane of proximal tubular cells. OCT2 facilitates the entry step of the vectorial transport of most cations from the peritubular space into the urine. OCT2 downregulation in kidney disease models is apparent, yet not clear from a mechanistic vantage point. The aim of this study was to explore the role of inflammation, a common thread in kidney disease, and NF-kB in OCT2 modulation and tubular secretion. Among the OCTs, OCT2 was found consistently downregulated in the kidney of rats with chronic kidney disease (CKD) or acute kidney injury (AKI) and in patients diagnosed with CKD, and it was associated with the upregulation of TNFα renal expression. Exposure to TNFα reduced the expression and function of OCT2 in primary renal proximal tubule epithelial cells (RPTEC). Silencing or pharmacological inhibition of NF-kB rescued the expression of OCT2 in the presence of TNFα, indicating that OCT2 repression was NF-kB-dependent. In silico prediction coupled to gene reporter assay demonstrated the presence of at least one functional NF-kB cis-element upstream the transcription starting site of the SLC22A2 gene. Acute inflammation triggered by lipopolysaccharide injection induced TNFα expression and the downregulation of OCT2 in rat kidney. The inflammation did reduce the active secretion of the cation Rhodamine 123, with no impairment of the glomerular filtration. In conclusion, the NF-kB pathway plays a major role in the transcriptional regulation of OCT2 and, in turn, in the overall renal secretory capacity.

scholarly journals Synthesis of bile acid monosulphates by the isolated perfused rat kidney

1976 ◽  
Vol 156 (2) ◽  
pp. 339-345 ◽  
Author(s):  
J A Summerfield ◽  
J L Gollan ◽  
B H Billing
Keyword(s):  
Bile Acid ◽  
Chenodeoxycholic Acid ◽  
Lithocholic Acid ◽  
Rat Kidney ◽  
Free Medium ◽  
Perfused Rat Kidney ◽  
Free Bile Acid ◽  
Cholestatic Syndrome ◽  
Protein Free Medium ◽  
Isolated Rat

Perfusion of an isolated rat kidney with labelled bile acids, in a protein-free medium, resulted in the urinary excretion of the labelled bile acid, 3% being converted into polar metabolities in 1h. These metabolities were neither glycine nor taurine conjugates, nor bile acid glucuronides, and on solovolysis yielded the free bile acid. On t.l.c. the metabolite of [24-14C]lithocholic acid had the mobility of lithocholate 3-sulphate. The principal metabolite of [24-14C]chenodeoxycholic acid had the mobility of chenodeoxycholate 7-sulphate; trace amounts appeared as chenodeoxycholate 3-sulphate. [35S]sulphate was incorporated in chenodeoxycholic acid by the kidney, resulting in a similar pattern of sulphation. No disulphate salt of chenodeoxycholic acid was detected. These findings lend support to the hypothesis that renal synthesis may account for some of the bile acid sulphates present in urine in the cholestatic syndrome in man.

The effect of sodium taurocholate on proximal tubular reabsorption in the rat kidney

1987 ◽  
Vol 72 (1) ◽  
pp. 139-141 ◽  
Author(s):  
O. S. Better ◽  
V. Guckian ◽  
G. Giebisch ◽  
R. Green
Keyword(s):  
Proximal Tubule ◽  
Bile Salts ◽  
Rat Kidney ◽  
Sodium Taurocholate ◽  
Tubular Reabsorption ◽  
Major Site ◽  
Proximal Tubular ◽  
Tubular Fluid Reabsorption ◽  
Proximal Tubular Reabsorption

1. Microperfusion of tubules in situ was used to study the direct effect of sodium taurocholate on reabsorption of fluid by the proximal tubule of the rat. 2. Sodium taurocholate (0.1 mmol/l) in the tubular perfusate reduced proximal tubular fluid reabsorption by approximately 30%. 3. Thus, the proximal tubule appears to be a major site at which bile salts cause a natriuresis in the rat, and possibly in obstructive jaundice in man.

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