PURPOSE: MATERIALS AND METHODS: Four groups of C57BL/6J mice were studied. Complete unilateral ureteral obstruction was created by ligating the right ureter at age 8 weeks. A single daily intraperitoneal injection of 30 mg./kg. S-methyl-L-thiocitrulline (SMLT), a selective neuronal and endothelial NOS inhibitor was started 24 hours before ureteral obstruction and administered to half of the study animals. SMLT treated mice and control animals were further subdivided to receive either regular tap water or 1% L-arginine (weight/volume) supplemented water after unilateral ureteral obstruction. Animals were sacrificed on postoperative day 3, 7 or 14. In addition, eNOS knockout mice with unilateral ureteral obstruction were given tap water or L-arginine supplemented water to drink and sacrificed after 14 days. Urine specimens from the bladder and the obstructed renal pelvis along with serum were collected. Nitrite level in each fluid was determined. Renal morphology and cortical thickness were assessed in the normal and obstructed kidneys. Interstitial fibrosis was evaluated using trichrome stain. RESULTS: SMLT was well tolerated by C57BL/6J mice. Serum nitrite levels and nitrite excretion in bladder urine were similar in all SMLT treated groups throughout the duration of unilateral ureteral obstruction. A reduction of pelvic urine nitrite levels by 89%, 68% and 48% versus bladder urine nitrite levels was observed after 3, 7 and 14 days of unilateral ureteral obstruction (p <0.05). Administration of SMLT resulted in a significant increase in bladder urine nitrite level at 7 days and in pelvic urine nitrite levels at 14 days. No significant histological differences in the obstructed kidney were seen after 3, 7 or 14 days of unilateral ureteral obstruction in SMLT treated versus control mice regardless of whether they received tap water or L-arginine supplemented drinking water. In eNOS knockout mice with unilateral ureteral obstruction for 14 days L-arginine supplementation had no effect on pelvic urine nitrite levels and did not alter renal histopathology or cortical thickness. CONCLUSIONS: NO production is decreased in the obstructed kidney in mice with unilateral ureteral obstruction. Biochemical inhibition of constitutive NOS did not modulate renal injury after 14 days of unilateral ureteral obstruction. In contrast to previous findings with iNOS knockout mice, dietary supplementation with L-arginine had no effect on the degree of fibrosis in the obstructed kidney in SMLT treated C57BL/6J or eNOS knockout mice. We conclude that NO derived from eNOS within the kidney has a pivotal role in protecting against renal fibrosis in response to unilateral ureteral obstruction.
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