Many neutered female dogs develop involuntary urine loss, designated as urethral sphincter mechanism incompetence. Treatment is primarily medical and involves increased closure pressure on the urethral sphincter. Collagen types I and III are associated with strength and flexibility in soft tissues. Stiffness is increased by collagen I, and flexibility is increased by collagen III, suggesting that the supportive tissues of the pelvic floor in dogs may be composed of a lower CIII:CI ratio in neutered females. This would result in stiffer support tissues and increased incontinence. Therefore, the CIII:CI ratios in neutered (n = 8) and intact (n = 34) female dogs (euthanized for nonurinary causes) were examined in the present study. Urethral tissue samples from each dog were analyzed by indirect double immunofluorescent CI and CIII staining and examined by fluorescent microscopy to determine CIII:CI ratio area fractions and total area values. The ratio of CIII:CI total area or area fraction did not significantly differ between the groups, suggesting that support structure composition may not strongly contribute to urinary incontinence in neutered female dogs.

Commentary: It was unclear whether any of the dogs included in the study had urethral sphincter mechanism incompetence. Future studies with larger sample sizes and evaluation of dogs with a history of clinical incontinence would better define such a model in dogs. The cause of such incontinence in veterinary patients is probably multifactorial and complex, and a complete understanding of its pathophysiology will allow more targeted treatment.

Evaluation of the ratio of collagen type III to collagen type I in periurethral tissues of sexually intact and neutered female dogs. Byron JK, Graves TK, Becker MD, et al. AM J VET RES 71:697-700, 2010.