Protective Effects of Cinnamaldehyde Against Heat Stress in Mice and Its Regulatory Influence on Estrogen Secretion

Heat stress (HS) causes reproductive damage in female mammals, including pigs, cattle, and sheep. As the primary site of estrogen (E2) biosynthesis, follicular granulosa cells (GCs) act as the critical target of HS injury. Previous studies have shown that cinnamaldehyde (CA) effectively participates in reproductive regulation in mice. Therefore, female mice and their follicular GCs were taken as the research subjects in this study. First, we adopted ELISA and H&E staining to investigate the effects of CA on ovarian follicular histology and E2 secretion in mice. Second, CCK-8 assay, flow cytometry, and ELISA were applied to clarify how CA regulates proliferation, apoptosis, and E2 secretion of mouse follicular GCs under HS. Finally, RT-qPCR and Western blotting (WB) were used to elucidate the protective effects of CA together with its underlying molecular mechanisms. Animal experiment results revealed that HS elevated the proportion of primordial and primary follicles and suppressed E2 secretion. Oral gavage of mice with CA at 25 mg/kg exhibited no obvious hepatotoxicity. This dosage effectively increased the percentage of secondary and antral follicles, alleviated HS-induced histological damage in ovaries, and raised serum E2 levels both under normal conditions and HS. Further in vitro cell experiments confirmed that HS reduced cell viability and accelerated apoptosis in mouse follicular GCs. HS decreased estrogen secretion by downregulating the relative protein expression of StAR and CYP19A1. Treatment with CA at a concentration of 2.5 × 10−5 M significantly increased cell viability and inhibited excessive apoptosis in mouse follicular GCs under HS. Under HS conditions, CA treatment elevated E2 secretion in mouse follicular GCs by upregulating the relative protein expression of StAR and CYP19A1. In conclusion, the findings of this study indicate that CA holds promise as a natural anti-HS additive.