Shyan-Yih Chou

Tubulointerstitial fibrosis, the histological feature of chronic obstructive nephropathy, is delineated in complete unilateral ureteral obstruction models. Histological changes during chronic partial ureteral obstruction are not well studied. We describe changes in a rat model of partial ureteral obstruction. We examined the effects of atorvastatin on histological alterations, fibrosis and function in this model. All rats underwent right nephrectomy. To create partial ureteral obstruction the left ureter was incorporated into the psoas muscle, which was split and reapproximated. Excretory urogram, histology, Western blot of alpha-smooth muscle actin and renal clearance were examined in rats with sham, 14-day or 30-day partial ureteral obstruction. Obstructed rats received a regular or a diet supplemented with 50 mg/kg body weight atorvastatin per day. At 14 days of partial ureteral obstruction pyelogram showed hydronephrosis, which was more pronounced on obstruction day 30. Histological studies on obstruction days 14 and 30 revealed tubulointerstitial fibrosis in the medulla and cortex. Atorvastatin significantly decreased tubulointerstitial fibrosis seen in alpha-smooth muscle actin expression. On obstruction day 14 or 30 the glomerular filtration rate in rats on a regular diet was significantly lower than in sham PUO rats or rats on atorvastatin. This model of partial ureteral obstruction enables chronic studies of morphological and histological changes of the obstructed kidney. It showed progressive fibrosis and decreased filtration function. Atorvastatin ameliorated fibrosis and helped preserve kidney filtration function.

Purpose: The pleiotropic effects of hMG-CoA (3-hydroxy-3-metylglutaryl coenzyme A) reductase inhibitors may provide renal protection in chronic kidney disease. We examined whether atorvastatin administration preserved renal function in rats with chronic unilateral ureteral obstruction. Materials and Methods: Renal clearance experiments were performed in sham operated rats and rats subjected to 3 or 12-day unilateral ureteral obstruction. Hemodynamics parameters and urinary microalbumin levels from the obstructed kidney were also measured. The rats were maintained on a regular diet or the same diet but supplemented with atorvastatin (50 mg/kg daily). Results: Atorvastatin administration did not alter plasma total cholesterol but it significantly decreased triglyceride levels. In sham operated and 3-day unilateral ureteral obstruction rats atorvastatin treatment did not have effects on the glomerular filtration rate or effective renal plasma flow and it also did not affect urinary microalbumin levels. In rats with 12-day unilateral ureteral obstruction the glomerular filtration rate but not effective renal plasma flow was significantly higher and urinary microalbumin was significantly lower in atorvastatin treated rats than in those without atorvastatin treatment. Conclusions: Atorvastatin treatment decreased microalbuminuria and helped preserve filtration function in chronic unilateral ureteral obstruction without altering plasma cholesterol levels, suggesting that pleiotropic renal protection is offered by this statin.

Cinacalcet, a novel calcimimetic compound, is effective in reducing parathyroid hormone (PTH) levels in approximately 70% of patients with secondary hyperparathyroidism. However, interindividual variations in the dose required to achieve the treatment goal have been noted in clinical studies. Our investigation examined the genetic polymorphisms of the calcium-sensing receptor (CaSR) gene as one possible cause of the different responses to cinacalcet. We report data on seven end-stage renal failure patients who were treated with regular haemodialysis and who participated in clinical trials of cinacalcet. All patients had secondary hyperparathyroidism with baseline intact PTH (iPTH) levels greater than 600 pg/ml. Three patients were male and four female with a mean±SD age of 60±12 years. DNA was extracted from peripheral lymphocytes. An area in exon 7 of the CaSR gene was amplified by the polymerase chain reaction and sequenced. Mean±SD baseline iPTH was 1086±189 pg/ml. The five patients without Arg990Gly demonstrated a 29.7±4.0% (±SEM) reduction in iPTH from individual baseline. One patient was found to be homozygous for the Arg990Gly polymorphism and another was heterozygous for both arginine and glycine alleles. The homozygous patient showed a significantly higher sensitivity to cinacalcet compared to the other patients (P=0.003) with a 76.3±7.7% reduction in iPTH from baseline. No polymorphisms were noted in codons 986 or 1011. This preliminary study points to the possibility that patients homozygous for glycine at the 990 position in exon 7 of the CaSR may be more sensitive to the calcimimetic drug cinacalcet compared to those who are homozygous for arginine at that location.

Unilateral ureteral obstruction (UUO) for 21 hours causes severe renal vasoconstriction. We examined the role of endothelin (ET)-A receptor in renal hemodynamic alterations induced by UUO. Hemodynamic and clearance experiments were performed in 3 groups of anesthetized dogs. In group 1, 6 sham operated dogs received intrarenal infusion of the specific ET-A receptor antagonist BQ-610 (Peninsula Laboratories, Inc., Belmont, California), followed by infusion of the nitric oxide synthase substrate L-arginine. In the 7 group 2 dogs release of 21-hour UUO was followed by intrarenal infusion of BQ-610 and L-arginine. In the 5 group 3 dogs release of 21-hour UUO was followed by L-arginine infusion. UUO caused marked decreases in renal blood flow (RBF) and glomerular filtration rate (GFR) in groups 2 and 3 compared with group 1. In group 1 BQ-610 and L-arginine infusion did not alter RBF or GFR. In contrast, BQ-610 infusion in group 2 after UUO release led to a significant increase in RBF and GFR as well as additional increases after L-arginine infusion. After UUO release in group 3 L-arginine infusion alone did not change RBF or GFR. After UUO release blockade of the ET-A receptor ameliorates renal vasoconstriction. The addition of L-arginine, which is a substrate for nitric oxide synthase, superimposed on ET-A receptor blockade confers a further decrease in renal vascular resistance, suggesting that the ET and L-arginine-nitric oxide systems are involved in renal hemodynamic alterations caused by UUO.

The cyclooxygenase (COX) pathway is activated in unilateral ureteral obstruction (UUO), contributing to renal hemodynamic alterations in different regions of the kidney. After the release of 24-hour UUO cortical vasoconstriction occurs but medullary hyperemia is seen. We examined the expression of the 2 COX isoforms COX-1 and COX-2 in different regions of the kidney in rats subjected to UUO. Clearance experiments were performed after ureteral obstruction release in rats with 24-hour UUO or sham operated rats. COX-1 and COX-2 expression in the cortex and medulla were examined by Western blot analysis and immunohistochemistry. After UUO release the glomerular filtration rate and renal plasma flow were markedly lower in post-obstructed kidneys than in contralateral kidneys or in kidneys in sham operated rats (p <0.001). Western blot analysis showed that COX-2/β-actin in the cortex of the obstructed kidney was 0.28 ± 0.02 densitometry units, significantly lower than 0.67 ± 0.12 densitometry units in the contralateral unobstructed kidney. In contrast, COX-2/β-actin in the outer and inner medullae of the obstructed kidney was 7.85 ± 1.09 and 2.51 ± 0.14 densitometry units, significantly greater than 3.03 ± 0.22 and 0.66 ± 0.14 densitometry units, respectively, in the contralateral unobstructed kidney. The expression of COX-1/β-actin in the obstructed kidney was similar to that in the contralateral unobstructed kidney in the cortex and medulla. Renal COX-2 expression is markedly altered in UUO. Decreased cortical expression of COX-2 and markedly increased expression in the medulla may contribute to disparate regional hemodynamic alterations in UUO.

In the early stage of unilateral ureteral obstruction total renal blood flow increases but medullary blood flow decreases, exacerbating medullary tissue hypoxia. We examined the expression of inducible nitric oxide synthase, a product of a hypoxia sensitive gene, in the cortex and medulla in dogs with unilateral ureteral obstruction for 21 hours. Hemodynamic and clearance experiments were performed after release of ureteral obstruction in 6 dogs with unilateral ureteral obstruction, followed by Western blot analysis of nitric oxide synthase and immunohistochemistry. Ureteral obstruction raised mean ureteral pressure plus or minus standard error to 35.0 ± 7.2 mm. Hg. In dogs with unilateral ureteral obstruction mean renal blood flow was 116 ± 10 ml. per minute, lower than the 213 ± 22 ml. per minute in sham operated dogs (p <0.01). After unilateral ureteral obstruction release the mean glomerular filtration rate was 9.5 ± 2.1 ml. per minute, lower than the 27.3 ± 1.8 ml. per minute in the contralateral unobstructed kidney (p <0.01). Western blot analysis showed that mean nitric oxide synthase/β-actin in the cortex of the obstructed kidney was 0.04 ± 0.01 densitometry units, lower than 0.11 ± 0.02 densitometry units in the unobstructed contralateral kidney (p <0.05). In contrast, mean nitric oxide synthase/β-actin in the medulla of the obstructed kidney was 1.29 ± 0.33 densitometry units, greater than the 0.34 ± 0.03 densitometry units in the unobstructed kidney (p <0.05). Immunohistochemistry revealed that the increased expression of nitric oxide synthase protein was localized to the endothelium of the vasa recta. Unilateral ureteral obstruction enhances nitric oxide synthase expression in the medulla but not in the cortex. This increased expression in the medulla may be the result of increased medullary hypoxia in unilateral ureteral obstruction, possibly contributing to medullary hyperemia after unilateral ureteral obstruction release.

Purpose: Endothelin-1 (ET-1), a peptide produced by the vascular endothelium, causes profound renal vasoconstriction by binding to ET-A receptors. The present study examined the renal actions of ET-1 after ET-A receptors were blocked by BE-18257B to unmask the functions of ET-B receptors. Materials and Methods: Renal hemodynamics and clearance measurements were obtained in anesthetized dogs after intrarenal infusion of BE-18257B at 100 ng./kg./min. (Group 1), after intrarenal infusion of ET-1 at 2 ng./kg./min. (Group 2), or after intrarenal infusion of ET-1 superimposed on BE-18257B (Group 3). Results: In Group 1, BE-18257B infusion did not alter arterial pressure, renal blood flow (RBF), GFR or tubular function. In Group 2, ET-1 infusion led to a significant decrease in RBF and GFR (37 and 40%, respectively) without altering arterial pressure. Urinary volume and sodium excretion were not changed but osmolality decreased significantly. In Group 3, BE-18257B infusion significantly attenuated the decrease in RBF caused by ET-1 and increased GFR by 40% without altering arterial pressure, associated with significant diuresis and natriuresis. Conclusion: Renal vasoconstriction caused by ET-1 is attenuated by ET-A receptor blockade with BE-18257B, which unmasks the hemodynamic and tubular actions of ET-B receptors. As a result, it limits the ET-1 induced decrease in RBF and raises GFR, and leads to a diuresis and natriuresis.