Effect of the duration of bladder overdistention on renal function and morphology in rats

The aim of this study was to investigate the influence of the duration of bladder overdistention (DOBO) on kidney structure and function in rats. Bladder overdistention was induced in male Sprague-Dawley rats by an infusion of saline. Forty rats were divided into five groups: DOBO 1, 2, 4 or 8 h groups and the control. Renal function was evaluated using serum creatinine (SCr) and blood urea nitrogen (BUN). Apoptotic indices and morphologic changes of the kidney were detected by terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling (TUNEL) staining and transmission electron microscopy (TEM). Compared with the control, rats undergoing 2, 4 or 8 h of overdistention showed significant, time-dependent increases in SCr (12.375 vs. 23.125, 34.375 and 51.500 μmol/l, respectively), BUN (6.980 vs. 18.689, 25.184 and 32.079 mmol/l, respectively), renal size (1.041 vs. 1.472, 1.484 and 1.634 cm(3), respectively) and renal pelvis separation (0.000 vs. 0.223, 0.320, 0.308 and 0.277 cm, respectively; P<0.01). In the rats, 2, 4 and 8 h of overdistention elicited time-dependent increases in the blood flow rate in the main renal artery (MRA; 44.827 vs. 49.082, 59.688 and 67.123 cm(3)/sec, control vs. DOBO 2, 4 and 8 h), the interlobar renal artery (IRA; 32.095 vs. 39.16 and 51.745 cm(3)/sec, control vs. DOBO 4 and 8 h) and the segmental renal artery (SRA; 21.171 vs. 24.355 and 25.358 cm(3)/sec, control vs. DOBO 4 and 8 h; P<0.01). TUNEL results showed that prolonged overdistention increased the apoptotic index of renal cells significantly (1.15, 1.77, 3.40, 5.34 and 13.91% for control and DOBO 1, 2, 4 and 8 h, respectively; P<0.01) and TEM indicated that prolonged overdistention resulted in ultrastructural injuries of increased severity. DOBO plays a significant role in the functional and structural impairment of the rat kidney. With increasing duration, the hemodynamic changes, cell apoptosis and ultrastructural injuries of the kidney are more evident, all of which may contribute to the increasingly serious impairment of renal function and morphology.