Analysis of primary urethral wound healing in the rat.

Objective: To analyze the process of urethral healing, which is the basis of urethral reconstructive surgery but remains poorly understood, we have developed a rat model of urethroplasty. Understanding this process may provide strategies to prevent aberrant urethral healing and improve the healing process.

Methods: We performed urethroplasties on 36 male Sprague-Dawley rats. On postoperative days 2, 4, 6, 8, 10, and 12, animals were sacrificed. The number of neutrophils, macrophages, fibroblasts, blood vessels, and Ki67 proliferative index was evaluated with immunostaining and collagen I and III contents with picrosirius staining. Expression of VEGF, PDGF, TNFα, TGFβ, and FGF was analyzed with quantitative real-time PCR.

Results: Urethral healing occurs in phases of inflammation, proliferation, maturation, and remodeling analogous to dermal healing, however, with extended duration of each phase. The inflammatory phase reached to postoperative day 4 being characterized by neutrophil and macrophage predominance and high levels of VEGF, PDGF, TGFβ, TNFα, and IL-10. The proliferative phase extended until day 10 characterized by myofibroblast proliferation and angiogenesis. Maturation and remodeling started on day 10 with decreasing proliferation and angiogenesis, increasing collagen I formation, and periurethral alignment of connective tissue. The healing process involved >50% of the periurethral/spongiosum area in the inflammatory and >80% in the maturation and remodeling phase.

Conclusion: Urethral healing occurs in phases similar to those observed in dermal healing, however, with extension of each phase. The healing process is not limited to the site of injury but involves the vast majority of periurethral tissue and corpus spongiosum. This appears to be the result of the unique anatomical features of the urethra.