BACKGROUND: Detrusor underactivity (DU) is a common lower urinary tract dysfunction, which can be manifested as a dual dysfunction of urinary storage and voiding. The nerve plexus innervating the bladder may be damaged by pelvic surgery, which may result in DU, increased residual urine and decreased bladder sensitivity, and even urine retention, seriously affecting patients' quality of life. In this study, we established an animal model of DU by squeezing the bilateral pelvic nerves of female rats and evaluated the urodynamic and histological changes, aiming to explore a safe, effective, stable and well-repeatable method of modelling DU in female rats. METHODS: Forty-five 10-12-week-old female SD rats weighing 210-230 g were selected and divided into bilateral pelvic nerve injury (BPNI)-1W, BPNI-4W and sham-operated groups (Sham group) according to the random number table method, with 15 rats in each group. In the BPNI group, the pelvic nerves were squeezed bilaterally, while in the Sham group, only the nerves were exposed but left untreated. After 1 week of surgery in the BPNI-1W group and 4 weeks of surgery in the BPNI-4W and Sham groups, urodynamic examination was performed, bladder tissue was collected for HE and Masson staining to observe histological changes, and immunohistochemistry and protein blotting were performed to detect a-SMA and Collagen I expression. RESULTS: Rats in the BPNI-1W group developed postoperative filling incontinence. The urinary function was partially recovered in the BPNI-4W group, the maximum bladder capacity was (8.84 ± 1.02) and (5.54 ± 1.42) ml in the BPNI-1W group and the BPNI-4W group, respectively. The residual urine was significantly higher than that of (8.31±1.05) and (4.16±1.37) ml in the Sham group [(3.35±0.39) ml and (0.11±0.03) ml, P <0.05], maximum intravesical pressure in BPNI-1W and BPNI-4W groups were (15.37±1.76) and (21.36±2.98) cmH2O, respectively. Masson staining of bladder tissue showed that the collagen volume fraction was 18.5%, 19.0%, and 36.3% in the Sham, BPNI -4W, and BPNI-4W groups, respectively, and the collagen volume fraction was significantly higher in the BPNI-4W group than that in the Sham and BPNI -1W groups (P < 0.05). HE staining showed thickening of the bladder wall and increased vacuolization of detrusor muscle in the BPNI-1W and BPNI-4W groups compared with the Sham group, and subplasma edema and inflammatory cell infiltration of the detrusor muscle were obvious in the BPNI-1W group; and the bladder weight ratios of the two groups were significantly increased compared with the Sham group. The expression of αSMA and Collagen I in bladder tissue was significantly higher in the BPNI-4W group compared with the BPNI-1W group and Sham, and there was no significant difference in the expression of αSMA in bladder tissue in the BPNI -1W and Sham groups.
CONCLUSIONS: By squeezing the bilateral pelvic nerves, a female rat DU model was successfully constructed, which showed increased bladder fibrosis, bladder wall thickening and impaired voiding function. Compared with that at 1W after BPNI, urodynamic parameters were partially recovered at 4W after BPNI, suggesting that early intervention is more clinically valuable.
