Histologic changes after urethroplasty using small intestinal submucosa unseeded with cells in rabbits with injured urethra.

Objective: To determine whether small intestine submucosa has the same regenerative capacity when urethroplasty is performed in injured urethras.

Methods: Our experiment was conducted in 30 New Zealand male rabbits, all of which had urethral injury. One month after the injury, the animals were randomized into a control group or a group with onlay urethroplasty with small intestine submucosa. The animals were euthanized at 2, 4, 12, 24, and 36 weeks after urethroplasty, and their urethras were removed for histologic and immunohistochemical examination. Before the scheduled euthanasia, urethrography and cystoscopy were performed.

Results: After 2 weeks, there was evidence of a continuous monolayer of stratified epithelial cells and absence of smooth muscle fibers. One month later, the epithelium showed no changes from the previously observed features, but some smooth muscle fibers (representing newly formed vessels) became apparent. After 3 months, the graft showed increased concentration of smooth muscle fibers. After 6 and 9 months, the density of smooth muscle cells remained unchanged. Fiber arrangement was irregular, particularly at the anastomosis site. Epithelial and smooth muscle phenotypes were confirmed by immunohistochemistry using anti-pan-citokeratin (AE1/AE3) antibodies and anti-α-smooth muscle actin, respectively.

Conclusion: Small intestine submucosa promotes regeneration in traumatized urethras, with slightly delayed epithelialization and abnormal distribution of smooth muscle. Urethral damage caused by trauma interferes with the normal healing process.