An atherosclerosis-induced chronic bladder ischemia (CBI) model has been established in male rats using balloon catheter insertion into the common iliac artery, effectively reproducing ischemia-related bladder dysfunction [1]. However, its application is limited to larger male rats. Given that ischemia-related lower urinary tract symptom (LUTS) also occurs in women [2], there is a need for a female-specific model. This study aimed to develop and validate a CBI model in female rats and assess mechanosensitive single-unit afferent activity (SAA) in bladder-innervating fibers.

Female Sprague–Dawley rats (9–11 weeks old) were assigned to sham or CBI groups (N=20 each). The CBI group received balloon-induced iliac artery injury and a 2% cholesterol diet for 8 weeks, while the sham group underwent bilateral inguinal incisions without injury and received a regular diet, following the same procedure used in male rats [1]. In the frequent voiding (FV) measurement, the rat was placed without any restraint in a metabolic cage. After adaptation, voided volume and voiding frequency were recorded continuously. After the FV measurement, the rats were sacrificed and bilateral common iliac arteries were harvested for histological examination. In the SAAs measurements, rats were anesthetized with urethane. Fine filaments were dissected from the left L6 dorsal roots and placed across a bipolar electrode for monitoring SAAs. Nerve fibers primarily originating from the bladder were identified by electrical stimulation of the left pelvic nerve and by bladder distension, and fibers with CV > 2.5 m/s were classified as Aδ-fibers; those with CV < 2.5 m/s as C-fibers [3]. The intravesical pressure and SAAs were recorded and analyzed during constant filling with saline until the intravesical pressure reached 30 cm H₂O.

In FV measurements, the CBI group showed significantly reduced mean voided volume during both the dark cycle and 24-h period (Fig. 1A). While voiding frequency and total volume showed no significant differences, the CBI group tended to void more frequently with less volume (Figs. 1B, C). HE staining revealed marked thickening of the iliac arterial walls in the CBI group (Fig. 1D), with quantitative analysis confirming significantly greater wall thickness than in the sham group (Fig. 1E). A total of 136 single afferent fibers were recorded. In the CBI group, Aδ-fiber SAAs were significantly higher than in the sham group at 10–15 and 15–20 cm H₂O, with no differences in other phases; cumulative SAAs showed a non-significant increase (Figs. 2A, C). In contrast, the CBI group showed significantly higher C-fiber SAAs (Figs. 2B, D).

We successfully established a female rat model of CBI using the same methods as in males—balloon-induced iliac artery injury and a cholesterol-rich diet. This model replicated key pathological and functional features seen in males [1], including arterial wall thickening and reduced mean voided volume, demonstrating its relevance for studying ischemia-induced bladder dysfunction in females. Notably, CBI selectively enhanced mechanosensitive C-fiber SAAs in female rats, supporting the role of chronic ischemia in abnormal C-fiber activation and the development of LUTS-related storage symptoms.

This study successfully established arteriosclerosis-induced CBI accompanied by frequent voiding in female rats, similar to males. In addition, the present findings suggest that C-fiber, but not Aδ-fiber, afferent activity is selectively facilitated under CBI conditions.

Nomiya M, Yamaguchi O, Andersson KE, Sagawa K, Aikawa K, Shishido K, Yanagida T, Kushida N, Yazaki J, Takahashi N: The effect of atherosclerosis-induced chronic bladder ischemia on bladder function in the rat. Neurourol Urodyn 2012, 31(1):195-200.
Pinggera GM, Mitterberger M, Steiner E, Pallwein L, Frauscher F, Aigner F, Bartsch G, Strasser H: Association of lower urinary tract symptoms and chronic ischaemia of the lower urinary tract in elderly women and men: assessment using colour Doppler ultrasonography. BJU Int 2008, 102(4):470-474.
Aizawa N, Igawa Y, Andersson KE, Iijima K, Nishizawa O, Wyndaele JJ: Effects of intravesical instillation of ATP on rat bladder primary afferent activity and its relationship with capsaicin-sensitivity. Neurourol Urodyn 2011, 30(1):163-168.