Ovarian support of pregnancy in ageing inbred mice.

The principal cause of reduced fertility in 10- to 12-month-old female CBA/H-T6 and CBA mice was found to be loss of embryos at the time of, or soon after, implantation. Treatment with exogenous progesterone, but not with oestradiol benzoate, increased the number of old females having implantation sites but did not increase either the average number of implantations/female or postimplantation survival to Day 10. When bovine prolactin or HCG was administered to pregnant old mice, the implantation rate was not increased. It was concluded that the function of the CL of pregnancy in old mice may have been impaired because the lutein cells were failing to respond adequately to the luteotrophic stimulus.