THE EFFECT OF THE TIME OF OESTROGEN INJECTION ON IMPLANTATION IN OVARIECTOMIZED PREGNANT MICE

Abstract

SUMMARY: Results have been obtained which indicate that the time of oestrogen administration during the pre-implantation period in the ovariectomized mouse may be critical for obtaining a maximum implantation response. In one series of experiments mated mice were ovariectomized on Day 3 of pregnancy and injected with oestradiol on each of Days 3, 4, 5 and 6. In other experiments ovariectomy was performed on Day 2 and oestradiol administered on each of Days 2, 3, 4, 5 and 6. Animals in both series of experiments received progesterone continuously after ovariectomy and implantation sites were scored on Day 10. The responses were the same in both series of experiments in that the number of mice with implantation sites and the number of sites per mouse increased as oestrogen was injected on each successive day during Days 2–5. A maximum response was obtained when oestrogen was injected on Days 5–6. Several possible explanations for these findings are discussed.