A novel animal model of long-term sustainable anal sphincter dysfunction

Although intersphincteric resection can avoid the need for permanent colostomy in patients with lower rectal cancer, it sometimes causes anal sphincter dysfunction, thus resulting in a lifelong, debilitating disorder due to incontinence of solid and liquid stool. The development of regenerative medicine could improve this condition by regenerating impaired anal muscle. In order to prove this hypothesis, preliminary experiments in animals will be indispensable; however, an adequate animal model is currently lacking. The purpose of this study was to establish a novel animal model with long-term sustainable anal sphincter dysfunction.

Twenty male Sprague-Dawley rats were allocated into sham operation (n = 10) and anal sphincter resection (ASR) (n = 10) groups. The ASR group underwent removal of the left half of both the internal and external anal sphincters. Both groups were evaluated for anal function by measuring their resting pressure before surgery and on postoperative day (POD) 1, 7, 14, and 28.

The rats in the sham operation group recovered their anal pressure up to baseline on POD 7. The rats in the ASR group showed a significant decrease in anal pressure on POD 1 (P < 0.0001) compared with the baseline, and kept this low pressure until POD 28 (P < 0.0001). The defect of the anal sphincter muscle was confirmed histologically in the ASR group on POD 28.

The present novel model exhibits continuous anal sphincter dysfunction for at least 1 mo and may contribute to further studies evaluating the efficacy of therapies such as regenerative medicine.