Hormonal Requirements of Implantation in the Rabbit.

Abstract

The role of ovarian hormones in implantation was studied in rabbits ovariectomized after mating and in ovariectomized pseudopregnant rabbits into which fertilized ova were transplanted. There was no evidence of delayed implantation. One to 3 implantations occurred in ovariectomized rabbits injected with 2-25 mg progesterone. The percentage of implantations ranged from 15 to 23 irrespective of dosage or the time at which injection started. Implantation failed to occur when the dose was 0.3 mg progesterone or 0.1 mg estradiol in combination with 2 or 25 mg progesterone. The number of implantations did not increase with the transplantation of ova. This may suggest a quantitative basis for the hormonal requirement at implantation. Hormonal requirements at implantation vary from those needed for subsequent development.