Introduction: Carbon nanotubes (CNTs), particularly multi-walled carbon nanotubes (MWCNTs), are increasingly used in aerospace-related materials. Weightlessness alone can alter hormonal regulation, oxidative stress, and reproductive physiology. The combined effects of MWCNT exposure and simulated weightlessness on female reproductive function remain poorly understood. Methods: Thirty adult female Wistar rats were assigned to five groups: control, Tween 80, weightlessness (simulated by hindlimb unloading), MWCNT injection, and weightlessness + MWCNT. Serum estradiol levels, ovarian size, follicle counts, histological features, and oxidative stress markers were evaluated after four weeks of treatment.

Results: Simulated weightlessness did not significantly alter serum estradiol levels but reduced ovarian size by 32%. In contrast, MWCNT exposure significantly increased estradiol levels and ovarian size. Combined exposure resulted in the highest estradiol concentrations and marked ovarian structural alterations, including the formation of cystic follicles. Furthermore, antioxidant enzyme activities (SOD and GPx) were significantly elevated only under combined exposure, whereas individual treatments produced minimal or non-significant effects. Both factors independently affected ovarian morphology, endocrine status, and oxidative balance, while their combined effects appeared distinct and partially additive.

Conclusion: Simulated weightlessness and MWCNT exposure each disrupt ovarian function, and their combination induces more pronounced reproductive alterations. These findings suggest potential reproductive health risks in environments involving both nanomaterial exposure and simulated weightlessness, highlighting the need for further research on underlying mechanisms, associated risk factors, and reversibility, particularly regarding female astronaut health.