Acute alterations in anorectal manometry induced by proximal and distal sphincterotomy. Experimental studies on piglets

Systematic Review of Animal Models Used in Research of Origins and Treatments of Fecal Incontinence

BACKGROUND

Fecal incontinence is a common disorder, but its pathophysiology is not completely understood.

OBJECTIVE

The aim of this review is to present animal models that have a place in the study of fecal incontinence.

DATA SOURCES

A literature review following Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines performed in August 2016 revealed 50 articles of interest. Search terms included fecal/faecal incontinence and animal model or specific species.

STUDY SELECTION

Articles not describing an animal model, in vitro studies, veterinary literature, reviews, and non-English articles were excluded.

MAIN OUTCOME MEASURES

The articles described models in rats (n = 31), dogs (n = 8), rabbits (n = 7), and pigs (n = 4).

RESULTS

Different fecal incontinence etiologies were modeled, including anal sphincter lesions (33 articles) ranging from a single anal sphincter cut to destruction of 50% of the anal sphincter by sharp dissection, electrocautery, or diathermy. Neuropathic fecal incontinence (12 articles) was achieved by complete or incomplete pudendal, pelvic, or inferior rectal nerve damage. Mixed fecal incontinence (5 articles) was modeled either by the inflation of pelvic balloons or an array of several lesions including nervous and muscular damage. Anal fistulas (2 articles), anal sphincter resection (3 articles), and diabetic neuropathy (2 articles) were studied to a lesser extent.

LIMITATIONS

Bias may have arisen from the authors' own work on fecal incontinence and the absence of blinding to the origins of articles.

CONCLUSIONS

Validated animal models representing the main etiologies of fecal incontinence exist, but no animal model to date represents the whole pathophysiology of fecal incontinence. Therefore, the individual research questions still dictate the choice of model and species.

Establishment of a new anal sphincter injury model in rats based on cardiotoxin

BACKGROUND/PURPOSE

Mainstream models for anal sphincter injury use large animals. We developed a simple and stable anal sphincter injury model in a small animal (i.e., rats) to obtain manometry measurements by using a miniaturized probe and applying cardiotoxin.

METHODS

The histological structure of the anal canal was evaluated by using manometry in normal rats (n=40). We damaged the internal and external anal sphincters by locally administering snake poison (cardiotoxin; 20 uM, 100μL 8 points). We evaluated the anal canal function through manometry measurements (n=5) and examined the histology using hematoxylin-eosin staining (at each time point, n=3; total n=15).

RESULTS

The manometry parameters and structure of the anal canal of normal rats were similar to those of humans, because rats have resting pressure, rectoanal reflex in the manometry, and an external and internal anal sphincter. After inducing injury, the following findings were observed: rhythmic wave loss and a remarkable reduction in the anal sphincter resting pressure; and local bleeding and advanced infiltration of the inflammatory cells (day 1) and the loss of muscle fibers (day 3).

CONCLUSION

This new rat model will contribute to increasing the knowledge on the anal canal.