Dynamics of post-ejaculated intrauterine environment in mice

After ejaculation, the intrauterine environment undergoes dynamic fluid changes due to post-ejaculated uterine fluid (eUF) coagulation and subsequent liquefaction. These changes presumably contribute to fertilization and reproductive efficiency; however, their physiological roles remain unclear. We studied the significance of the post-ejaculated intrauterine environment during in vivo fertilization. eUF coagulated immediately after ejaculation, and histological analysis of the uterus suggested that eUF liquefaction was promoted 6-10 h post-ejaculation. However, most gametes completed fertilization within 4 h post-ejaculation. Since eUF fluid changes did not align with fertilization timing, they are assumed to contribute to reproductive phenomena beyond sperm transport and release.