Establishment of a Male Rat Model Exhibiting Myogenic Underactive Bladder‐Like Features Following Bladder Cryoinjury

Objectives To establish a reproducible male rat model exhibiting myogenic underactive bladder (UAB)‐like features by applying bladder cryoinjury following direct saline instillation via fine‐needle puncture, thereby providing a useful platform for studying UAB pathophysiology and treatment. Methods Male Wistar rats underwent bladder cryoinjury using dry ice‐cooled aluminum rods placed on the bladder wall after filling the bladder with saline through a 30G needle. Sham‐operated rats received room‐temperature rod application. Two weeks post‐injury, continuous and single cystometry were performed to evaluate voiding pressure (VP), post‐void residual volume (PVR), and voiding efficiency (VE). Bladder strips were examined in organ bath studies for carbachol‐induced contractility. Hematoxylin and eosin staining was conducted for histological evaluation. Results Cryoinjured rats showed a significant increase in PVR and significant decreases in VP and VE compared to sham rats, indicating impaired voiding function consistent with UAB. No significant differences were observed in intercontraction interval or carbachol‐ or KCl‐induced contractile responses in bladder strips between cryoinjured and sham rats. In bladder sections, cryoinjury induced acute inflammation with neutrophil infiltration and notable appearance of foamy macrophages, suggesting phagocytic activity. Conclusions We established a practical and minimally invasive male rat model exhibiting myogenic UAB‐like features 2 weeks after cryoinjury. While ex vivo cholinergic and KCl‐evoked contractility was largely preserved at this time point, in vivo voiding remained impaired, suggesting contributions beyond muscle contractility. This model may facilitate mechanistic and therapeutic studies for UAB.