Maintenance of unimplanted fertilized ova in sprayed rats. IV. Effects of duration of ovarian hormone deprivation and progesterone therapy prior to the deprivation.

Studies were carried out in the spayed-rat delayed-implantation model to determine whether progesterone treatment prior to an ovarian hormone deprivation during the pre-implantation period would influence the incidence of subsequent delayed ovo-implantation induced with progesterone plus estrone. Implantation was rarely induced with 4 mg progesterone plus 1 microgram estrone/day after 5 to 11 days of ovarian hormone deprivation in rats that were spayed on Day 3, if progesterone treatment were not given before ovarian hormone deprivation. In contrast to this, implantation was fairly consistently induced with 4 mg progesterone plus 1 microgram estrone/day after 3, 5, 7, or 11 days of ovarian hormone deprivation in rats that were spayed on Day 3 and received 4 mg progesterone/day before the deprivation period (i.e., on Days 2 through 3, 2 through 6, or 2 through 8). The post-implantation viability of the embryos of the dams undergoing the longer periods of ovarian hormone deprivation, however, was reduced.