Study design, materials and methods
Twenty-four rats were assigned to the transected spinal nerves group (TSNG, n=8), transected spinal nerves+ losartan group (LSTG, n=8), and control group (CG, n=8). In TSNG, rats’ spinal nerves between L6 and S1 were transected completely. In LSTG, rats’ spinal nerves between L6 and S1 were transected completely and losartan was given orally. In CG, sham operation was performed. Bladder capacity (BC), bladder compliance (ΔC) in every group, bladder leakage pressure (Pves.leak) in TSNG and LSTG and bladder threshold pressure (Pves.thre) in CG were measured by cystometry at day 30 post-operation, Renal function was evaluated by ultrasound and blood biochemistry. The expression quantity of Angiotensin II (Ang II), Ang II type 1 receptor (AT1), transformation growth factor β1 (TGFβ1), collagen III and collagen fibrin in the bladder tissue were detected by immunofluorescence, ELISA, Weston blot and Masson staining. Data are presented as the mean ± standard error of measurement. Statistical analysis was carried out with SPSS version 17.0 statistical software package. The statistical significance of differences between groups was determined by ANOVA, followed by a least significant difference test for multiple comparisons. A P-value of less than 0.05 was considered to indicate statistical significance.
The rats in TSNG and LSTG couldn’t void voluntarily, their bladders lose the ability of autonomous contraction (Figure 1). ΔC in TSNG and LSTG decreased significantly compared to those of the CG (0.143±0.007 VS. 0.207±0.011 VS. 0.314±0.018), while, ΔC in LSTG was higher significantly than those of the TSNG, Pves.leak in TSNG and LSTG is higher significantly than Pves.thre of CG (55.373±4.015 cmH20, 43.986±2.047 cmH20 VS. 20.705±0.679 cmH20), in addition, Pves.leak in TSNG was higher than those of the LSTG. Renal function of both TSNG and LSTG decreased significantly compared to those of the CG, but renal function in LSTG was better than TSNG. Ang II of blood and bladder tissue in TSNG and LSTG increased significantly compared to CG. AT1 was expressed in bladder tissue of every group and obviously expressed in submucosa of bladder tissue. The TGFβ1, collagen III and collagen expression level (Figure 2) increased significantly in TSNG compared with LSTG and CG, while there was no significant different between CG and LSTG.
Interpretation of results
Bladder fibrosis is common in patients of NB and bladder fibrosis eventually damage renal function. Currently, there is no effective drug treatment for reversing bladder fibrosis, so it is important to look for ways to prevent the neurogenic bladder fibrosis.
Losartan is an AT1 blocker which is commonly used to treat hypertension in clinic. Previous studies have found Losartan could prevent colorectum, heart, liver and kidney fibrosis by blocking the combine of Ang II and AT1 in regulating TGFβ1/smads pathway. In this study, the degree of fibrosis in LSTG was significantly lower than TSNG,the expression quantity of TGFβ1 in the bladder tissues of LSTG was significantly lower thanTSNG. In addition AT1 been expressed in bladder tissues. These results indicated that losartan could prevent bladder fibrosis in NB by blocking the combination of Ang II and AT1 in down-regulating TGFβ1 too.
It’s well known that high bladder pressure for long time will lead to hydronephrosis which destroys kidney function. This study showed the rats in LSTG and TSNG produced hydronephrosis and renal impairment month 1 post-operation. These results may be because the bladders were chronically exposed to the high Pves.leak. Nevertheless, the level of hydronephrosis in LSTG was lesser than that in TSNG, which might because the Pves.leak in LSTG was slightly lower than TSNG. The reason for slightly lower Pves.leak in LSTG than TSNG may be associated with the little degree of bladder fibrosis in LSTG, because previous studies found that bladder neck fibrosis could increase the Pves.leak, however the specific mechanism needs to be study in the further. These findings may indicate that losartan could protect renal function though prevented bladder fibrosis in NB.