J Korean Med Sci.  2005 Apr;20(2):248-255. 10.3346/jkms.2005.20.2.248.

Angiotensin II AT1 Receptor Blockade Changes Expression of Renal Sodium Transporters in Rats with Chronic Renal Failure

• Kim EJ
• Jung YW
• Kwon TH

• KMID: 1095199
• DOI: http://doi.org/10.3346/jkms.2005.20.2.248

Abstract

We aimed to examine the effects of angiotensin II AT1 receptor blocker on the expression of major renal sodium transporters and aquaporin-2 (AQP2) in rats with chronic renal failure (CRF). During 2 wks after 5/6 nephrectomy or sham operation, both CRF rats (n=10) and sham-operated control rats (n=7) received a fixed amount of low sodium diet and had free access to water. CRF rats (n=10) were divided into two groups which were either candesartan-treated (CRF-C, n=4) or vehicletreated (CRF-V, n=6). Both CRF-C and CRF-V demonstrated azotemia, decreased GFR, polyuria, and decreased urine osmolality compared with sham-operated rats. When compared with CRF-V, CRF-C was associated with significantly higher BUN levels and lower remnant kidney weight. Semiquantitative immunoblotting demonstrated decreased AQP2 expression in both CRF-C (54% of control levels) and CRF-V (57%), whereas BSC-1 expression was increased in both CRF groups. Particularly, CRF-C was associated with higher BSC-1 expression (611%) compared with CRF-V (289%). In contrast, the expression of NHE3 (25%) and TSC (27%) was decreased in CRF-C, whereas no changes were observed in CRF-V. In conclusion, 1) candesartan treatment in an early phase of CRF is associated with decreased renal hypertrophy and increased BUN level; 2) decreased AQP2 level in CRF is likely to play a role in the decreased urine concentration, and the downregulation is not altered in response to candesartan treatment; 3) candesartan treatment decreases NHE3 and TSC expression; and 4) an increase of BSC-1 is prominent in candesartan-treated CRF rats, which could be associated with the increased delivery of sodium and water to the thick ascending limb.

Keyword

Angiotensin II; Aquaporins; BSC-1 Protein, rat; Kidney Failure; Vasopressins

MeSH Terms

Angiotensin II Type 1 Receptor Blockers
Animals
Aquaporins/genetics
Benzimidazoles/*pharmacology
Blood Urea Nitrogen
Kidney Failure, Chronic/drug therapy/*metabolism
Male
Organ Size/drug effects
Rats
Rats, Sprague-Dawley
Receptors, Drug/*genetics
Research Support, Non-U.S. Gov't
Sodium-Hydrogen Antiporter/*genetics
Sodium-Potassium-Chloride Symporters/*genetics
Symporters/*genetics
Tetrazoles/*pharmacology

Figure

• 

  Fig. 1 A diagram of the study design. CRF was induced in rats by right 2/3 nephrectomy followed by contralateral nephrectomy (n=10). Sham-operated control rats matching CRF rats (n=7). Both CRF rats and sham-operated control rats received a fixed amount of low sodium diet for 2 wks after induction of CRF. Two groups of CRF are made: CRF rats treated with vehicle (CRF-V, n=6) and CRF rats treated with candesartan (CRF-C, n=4). Sham-operated control rats were also treated with vehicle. The rats were maintained in metabolic cages at the days marked with asterisk (*), allowing monitoring of daily urine output and water intake. The stippled lines indicated the treatment of vehicle or candesartan in each group.

• 

  Fig. 2 Time course of the changes in urine output in CRF rats and sham-operated rats. Urine output was significantly increased after induction of 5/6 nephrectomy in CRF rats (both CRF-V (circle) and CRF-C (rectangle)), whereas there is no change in urine output after sham operation in control rats (triangle). *p<0.05 when CRF-V or CRF-C was compared with sham-operated control rats.

• 

  Fig. 3 Decreased expression of AQP2 in CRF-V and CRF-C. Immunoblot of whole kidney protein samples from CRF rats and sham-operated control rats. (A) The immunoblot was reacted with affinity purified anti-AQP2 and reveals 29 kDa and 35-50 kDa AQP2 bands, representing non-glycosylated and glycosylated forms of AQP2. (B) Densitometric analysis demonstrated a decrease in AQP2 expression in CRF-V and CRF-C, compared with sham-operated control rats (Sham). *p<0.05 when CRF-V or CRF-C was compared with sham-operated control rats.

• 

  Fig. 4 Increased expression of BSC-1 in CRF-V and CRF-C. Immunoblot of whole kidney protein samples from CRF and sham-operated control rats. (A) The immunoblot was reacted with affinity purified anti-BSC-1 and recognized a broad band of molecular mass 146-176 kDa. (B) Densitometric analysis revealed a significant increase of BSC-1 expression in CRF-V and CRF-C compared with sham-operated rats (Sham). Moreover, CRF-C was associated with higher BSC-1 expression compared with CRF-V. *p<0.05 when CRF-V or CRF-C was compared with sham-operated controls, †p<0.05 when CRF-C was compared with CRF-V.

• 

  Fig. 5 Decreased expression of NHE3 in CRF-C. Immunoblot of whole kidney protein samples from CRF and sham-operated rats. (A) The immunoblot was reacted with affinity purified anti-NHE3 and revealed a single ~87 kDa band. (B) Densitometric analysis revealed a marked decrease in NHE3 expression in the CRF-C, compared with CRF-V and sham-operated control rats (Sham). *p<0.05 when CRF-V or CRF-C was compared with sham-operated controls, †p<0.05 when CRF-C was compared with CRF-V.

• 

  Fig. 6 Decreased expression of TSC in CRF-C. Immunoblot of whole kidney protein samples from CRF and sham-operated rats. (A) The immunoblot was reacted with affinity purified anti-TSC and revealed a broad band centered at ~164 kDa band. (B) Densitometric analysis revealed a marked decrease in TSC expression in CRF-C, compared with CRF-V and sham-operated controls. *p<0.05 when CRF-V or CRF-C was compared with sham-operated controls, †p<0.05 when CRF-C was compared with CRF-V.

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