Phosphodiesterase-5 Inhibitor Sildenafil Pretreatment Attenuates Apoptosis and Intestinal Injury in a Rat Model of Necrotizing Enterocolitis

Background Necrotising enterocolitis (NEC) is a devastating gastrointestinal disease of premature infants, in which hypoxia-induced apoptosis plays a critical role in intestinal epithelial injury. The balance between pro-apoptotic and anti-apoptotic proteins, particularly Bax and Bcl-2, as well as the hypoxia-responsive transcription factor HIF-1α, are key determinants of epithelial survival.. Sildenafil citrate, a phosphodiesterase-5 inhibitor, has been shown to improve microcirculation and exert anti-apoptotic effects through nitric oxide–cGMP signalling, but its role in NEC remains poorly understood.This study aimed to evaluate the protective effects of sildenafil on NEC-induced apoptosis in rat pups. Methods A total of 75 Wistar rat pups were randomly assigned to six groups: control, NEC, SF + DMSO, and sildenafil-treated groups (1, 5, and 10 mg/kg/day). Sildenafil was administered intraperitoneally for 4 days before NEC induction. NEC was induced by hypoxia (100% nitrogen for 60 seconds, twice daily for 48 hours) and followed by cold stress (10 minutes at 4°C).Intestinal tissues were collected for histopathological scoring, caspase-3 immunohistochemistry, and quantitative RT-PCR analysis of HIF-1α, Bax, and Bcl-2 expression. Data were analyzed using ANOVA and Kruskal–Wallis tests, with p ≤ 0.05 considered statistically significant Results NEC pups exhibited severe villous damage, elevated histological injury scores, and marked upregulation of HIF-1α and Bax, along with downregulation of Bcl-2. Caspase-3 immunoreactivity strongly correlated with histological injury (Spearman’s ρ = 0.795, p < 0.001). Sildenafil reduced histological damage and apoptosis in a dose-dependent manner. The Sil_10 group showed the lowest injury score (1.06 ± 0.4, p < 0.0001 vs NEC), significantly reduced Caspase-3 labeling, suppressed Bax and HIF-1α expression, and increased Bcl-2 levels, resulting in a markedly reduced Bax/Bcl-2 ratio compared with NEC (p < 0.0001). Conclusions Sildenafil attenuates NEC-associated intestinal injury by modulating apoptotic and hypoxia-related pathways, lowering HIF-1α expression, reducing Bax/Bcl-2 ratio, and preserving epithelial integrity. These findings provide novel histological and molecular evidence for the anti-apoptotic effects of sildenafil in experimental NEC and highlight HIF-1α modulation as a potential therapeutic strategy.