Objective To investigate the potential role of estrogen in the formation of granulation tissue hyperplasia-induced tracheal stenosis in rats.

Methods Twenty-four female SD rats were randomly divided into three groups (n= 8) using a random number table method: sham group (n=8), ovariectomized (OVX) group (bilateral ovariectomy, n=8), and ovariectomized+estrogen (OVX+E₂) group (bilateral ovariectomy followed by exogenous estrogen intervention, n=8). Four weeks after establishment of the Sham and OVX rat models, a granulation tissue hyperplasia-induced tracheal stenosis model was constructed in all rats using the oral nylon brush scraping method. On the first day of modeling, rats in the OVX+E₂ group were administered 17β-E₂ at a dose of 300 μg/kg via intraperitonealinjection daily, while rats in the other two groups were given the same volume of normal saline. After 7 consecutive days of administration, tracheal specimens were obtained. Hematoxylin and eosin (HE) staining was used to observe the pathological changes of tracheal granulation tissue hyperplasia in each group and calculate the tracheal stenosis rate. Masson staining was employed to analyze the collagen fibers in the tracheal granulation tissue and calculate the relative collagen deposition area. Immunohistochemical (IHC) staining was used to detect the protein expression levels of transforming growth factor-beta 1 (TGF-β1), vascular endothelial growth factor (VEGF), alpha-smooth muscle actin (α-SMA), and collagen type Ⅰ (COL-Ⅰ) in the tracheal granulation tissue, and the average optical density (AOD) was calculated.

Results HE staining revealed granulation tissue hyperplasia and tracheal lumen stenosis in the tracheal walls of all three groups. The stenosis rate was the highest in the OVX+E₂ group, followed by the sham group, and the lowest in the OVX group, with statistically significant differences (P < 0.05). Masson staining showed that the collagen fibers in the sham group were thicker and denser with more collagen deposition compared to the OVX group. In contrast, the OVX+E₂ group had even thicker and denser collagen fibers with more collagen deposition than the sham group. IHC staining demonstrated that the protein expression levels of COL-Ⅰ, TGF-β1, VEGF, and α-SMA in the tracheal granulation tissue were the lowest in the OVX group, followed by the sham group, and the highest in the OVX+E₂ group.

Conclusion Estrogen can accelerate tracheal granulation tissue hyperplasia by upregulating the protein expression levels of COL-Ⅰ, TGF-β1, and VEGF, as well as promoting fibroblast activation, leading to aggravated tracheal stenosis.