[Urodynamic and histological evaluation of cyclophosphamide-induced bladder pain syndrome in SD rats]

To establish a model of bladder pain syndrome in SD rats by cyclophosphamide intraperitoneal injection, to evaluate the effectiveness of the model from the urodynamic and histological levels, to lay a zoological foundation for the clinical study of bladder pain syndrome, and to further guide clinical treatment.

Thirty-two 8-week-old SD rats were randomly divided into 4 groups, including acute test group, acute control group, chronic test group, and chronic control group, with 8 rats in each group. The acute test group received intraperitoneal injection of cyclophosphamide 150 mg/kg immediately after the measurement of urodynamic data on the first day, and urodynamic examination was performed again 2 days later. After that, the rats were sacrificed to obtain bladder tissue. In the chronic test group, after measuring the baseline data of urodynamics on the first day, cyclophosphamide 75 mg/kg was intraperitoneally injected on the first, fourth, and seventh days, and the rats were sacrificed after measuring the urodynamic data again on the eighth day to obtain bladder tissue. The acute control group and the chronic control group were injected with the same amount of normal saline during intraperitoneal injection, and the urodynamic testing time point were consistent with the corresponding test groups. Histopathological changes of the bladder were assessed by HE staining.

In each acute and chronic group, there were no intragroup differences in baseline urodynamic levels between the test and control groups. The urodynamic maximum bladder volume was significantly reduced in the acute test group after administration(t=-2.961, P < 0.05), histologically, severe interstitial edema, obvious inflammatory cell infiltration, mucosal edema and submucosal hemorrhage, and partial urothelium were absent could be seen, which were consistent with acute cystitis performance. The urodynamic maximum bladder capacity was significantly reduced in the chronic test group after administration (t=-3.886, P < 0.05), and the bladder compliance was lower than that in the control group, but not significant, the histological manifestations were urothelial exfoliation, interstitial edema, submucosal hemorrhage, infiltration of inflammatory cells such as lymphocytes, and dense vascular distribution.

In the acute test group, a single intraperitoneal injection of cyclophosphamide could induce acute bladder inflammation in the rats. In the chronic test group, repeated injections of cyclophosphamide could induce histological changes in chronic inflammation of chronic bladder pain syndrome in the rats. But the bladder function was not significantly impaired.