At the end of the exposure, the animals were killed by CO2 asphyxiation at 22:00 on the final day after all of the hamsters had been in the dark for at least 2 hr (Z. Wang, Xu, Mou, Kong, Wu,et al., 2020). Blood samples were immediately collected after sacrifice and stored at 4°C for 30 min, then centrifuged at 3,000 rpm for 15 min at 4°C. Serum MT, FSH, LH, and fecal TTE levels were estimated using an enzyme‐linked immunosorbent assay Labsystems Multiskan MS 352 (Shanghai Hengyuan Biological Technology Co.,Ltd., H‐40277, Shanghai, China). Testis and epididymis were removed and weighed. The right testis or epididymis was cut into three parts;one part was immersed in paraformaldehyde‐glutaraldehyde fixative for transmission electron microscopy (TEM), while the other two parts were immersed in 4% paraformaldehyde for paraffin and frozen section embedding. The left testis or epididymis was stored in a refrigerator at 80°C for subsequent western blot experiments.
