Renal response during acute unilateral ureteral obstruction in rats

The early renal response to unilateral ureteral occlusion (UUO) and its mechanism have been extensively studied in dogs but seldom discussed in the most frequently used laboratory animals, rats. The acute phase of the renal response to UUO was studied in female rats weighing 190-236 g. We recorded the ureteral pressure and changes in renal parameters throughout 120 minutes of UUO in control (US, UUO + saline, n = 10), L-arginine-treated (UA, n = 10), and right-nephrectomized rats (UO, UUO in one kidney, n = 9). Ureteral pressure increased in all three groups of rats after complete ureteral obstruction. The extent of the increase was not significantly different between US and UA rats but was significantly higher in the UO rats. In US rats, the cortical microvascular blood flow (CMVBF), measured by a laser Doppler flowmeter, declined significantly, from 321 +/- 10 perfusion units (PU) to 260 +/- 11 PU. The percentage of drop in CMVBF at 120 minutes of UUO was significantly greater in UO (25.7 +/- 3.8 %) than in US (19 +/- 2.1%) and in UA (14 +/- 2%) rats. Acute UUO reduced the glomerular filtration rate (GFR) in US and UO rats, whereas L-arginine attenuated this decrease. The excretion of nitrate/nitrite was increased after UUO. Giving N(G)-nitro-L-arginine methyl ester hydrochloride (L-NAME, 12 mg/kg/h) during UUO did not reduce CMVBF more severely. Western blot analysis of endothelial nitric oxide synthase expression in the renal cortex and medulla protein extracts revealed no differences between US and sham-operated rats. Acute UUO did not lead to renal hyperemia in rats. Reduction of nitric oxide during UUO might contribute to the decrease of renal circulation during UUO.