EFFECT OF COMBINATIONS OF PROGESTERONE AND OESTRONE ON THE DELAY OF NIDATION, IMPLANTATION AND FOETAL SURVIVAL IN OVARIECTOMIZED RATS

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Abstract
SUMMARY: One hundred and twenty inseminated rats were ovariectomized 3 days after coitus and assigned to twelve treatment groups. Eleven groups were injected subcutaneously daily from day 3 to day 8 with 250, 1000 or 4000μg. progesterone alone and in combination with 0·01 or 0·1 μg. oestrone. The remaining group was injected with corn oil. All animals were injected daily with 4000 μg. progesterone and 1 μg. oestrone from day 9 to day 24 after coitus. Implantation was usually prevented permanently when animals were injected with oestrone or corn oil only from day 3 to day 8. The remaining treatments caused delayed implantation of ova. The numbers of implantation sites in groups treated with progesterone alone or in combination with oestrone were compared. Differences between groups were due to the dose of progesterone, the number of implantation sites increasing with the dose of the steroid. Addition of 0·01 or 0·1 μg. oestrone had no significant effect on the implantation site response. Survival of embryos after implantation decreased with increasing pre-nidation doses of progesterone in the absence of oestrone. In general, addition of oestrone to progesterone increased survival when oestrone was combined with the high dose of progesterone and decreased survival with the low dose of progesterone. Oestrone (0·01 μg.) given with progesterone produced consistently more frequent embryonic survival than addition of 0·1 μg. oestrone, regardless of the amount of progesterone given.