Maintenance of Postimplantation-Pregnancy in the Rat in the Presence of Ectopic Corpora Lutea: Requirement for Ovarian Follicles and Estrogen12

Ectopic corpora lutea were established in rats by autotransplantation of follicles under the kidney capsule on the afternoon of proestrus. These ectopic corpora lutea were subsequently tested for their capacity to secrete the steroids required for the maintenance of pregnancy after implantation. Following ovariectomy on days 7, 9, or 11 of pregnancy (day 0 is proestrus, the day of follicle autotransplantation) 16 of 23 rats aborted. Of the 7 animals that remained pregnant, 5 were observed to have one or more large ectopic follicles on the kidney surface, adjacent to ectopic corpora lutea. In another group of animals (4), the corpora lutea in situwere excised on day 7 leaving the remaining ovarian constituents intact. All animals remained pregnant, demonstrating the capacity of ectopic corpora lutea to secrete progestational steroids. Administration of estradiol-17β(0.1 μg per day in oil, sc) maintained pregnancies in 8 of 9 rats ovariectomized on day 7; with one exception, the administration of LH (NIH-S-14) and/or prolactin (NIH-S-8; -S-9) failed to prevent abortions. These data indicate that secretions from corpora lutea are necessary but not sufficient for the maintenance of pregnancy following implantation. Follicular steroids, presumably estrogens, are required together with progesterone from corpora lutea to effect a suitable hormonal environment for the conceptus prior to day 12 of pregnancy. The requirement for estrogens derived from nonluteal ovarian tissues is transient, because pregnancies were maintained following ovariectomy on days 13 or 14 in animals with ectopic corpora lutea.