The decline of pregnancy rate and abnormal uterine responsiveness of steroid hormones in aging mice

Reproductive capacity in animals and women declines with increasing age. Although ovarian aging is considered as a main cause for the decline of pregnancy rate, whether uterine aging occurs remains unclear. Even if blastocysts are transferred from young donors to older pseudopregnant recipients, the rate of implantation is still low, suggesting the occurrence of uterine aging. In this study, we compared the pregnancy rate and the uterine responsiveness of steroid hormones in ovariectomized mice at age between 2- and 12-month-old. Compared to 2-month-old mice, there is a significant decrease of both pregnancy rate and the number of implantation sites in 12-month-old mice. In ovariectomized mice, the uterine responsiveness of steroid hormones is also significantly different between 2- and 12-month-old mice. On day 4, Muc1 and PR level in 12-month-old mice is significantly higher than that in 2-month-old mice, while Hand2 level is significantly lower in 12-month-old mice. Our data suggest that the abnormal responsiveness of steroid hormones may contribute to the decline of pregnancy rate in 12-month-old mice.