Histological characteristics of injection, operation, and control proximal urethras. The proximal urethra in injection rats showed mild smooth muscle hypertrophy without epithelial proliferation and suburothelium inflammation (A) similar to the control (C). Epithelial proliferation and inflammation were seen around the urethra ligation in the surgery group (B). Injected hyaluronic acid is indicated with an arrow (D). Squamous metaplasia because of severe epithelial proliferation and inflammation is indicated with an asterisk in the surgery group (E).