Maintenance of unimplanted fertilized ova in spayed rats: effects of cortisone acetate therapy during the period of embryonic diapause.

Rat dams were ovariectomized on day 3 of pregnancy and treated with corn oil (0.25 ml/day), progesterone (4 mg/day), cortisone acetate (2 or 10 mg/day), cortisone acetate (10 mg/day) plus progesterone (4 mg/day) or progesterone (4 mg/day) plus oestrone (1 microgram/day) from days 2 to 8 or 14, followed by 6 to 11 days of treatment with progesterone (4 mg/day) plus oestrone (1 microgram/day). Implantation of ova at the normal time was realized in the animals treated from day 2 with progesterone plus oestrone. Implantation of ova was only realized subsequent to progesterone plus oestrone in the dams treated with progesterone alone, cortisone acetate alone, or progesterone plus cortisone acetate, except for one animal in the latter group. Implantation of ova was not usually realized even after progesterone plus oestrone treatment in the dams treated with corn oil. Even though cortisone acetate maintained unimplanted ova in spayed rats in much the same manner as does progesterone, it was not equivalent to progesterone in efficacy or action.