Further observations on the effects of oestradiol on tubal eggs and implantation in the guinea-pig.

Estradiol benzoate was injected subcutaneously into nonparous guinea pigs immediately after mating to study its effects on tubal eggs and implantation. Of 7 guinea pigs receiving a total of 5 or 6 mcg the first 3 days after mating 4 showed normal implantations at autopsy but of 8 that received 10 or 20 mcg only 2 did so (those which had the 10 mcg dose). The fallopian tubes of 15 other mated estrogen-treated guinea pigs were examined on Day 2 Day 4 or Day 5 postcoitum. Only 3 eggs were recovered from the tube and 3 from the uterus. 1 of the tubal eggs recovered on Day 4 postcoitum after 50 mcg estradiol benzoate was 8-celled and another on Day 2 was 4-celled. There was therefore no evidence of any tube-blocking of the eggs and it appeared that many eggs had been expelled or had failed to survive after passing prematurely into the uterus. In another group once the fertilized eggs had passed normally into the uterus (between Days 3-9) implantation was not prevented by as much as 30 or 50 mcg estradiol benzoate. The results indicated that the compound had interfered with the functioning corpora lutea which was confirmed by section through the ovaries which contained not only regressed corpora lutea but large follicles or corpora lutea from a fresh ovulation. 7 out of 8 females that received 20 mcg on Day 7 postcoitum had implanted and 6 of these had healthy embryos on Day 21. In animals which aborted or resorbed their embryos estrus returned about Day 16. Implantation was not inhibited by 20 mcg in guinea pigs ovariectomized on Day 5 and injected on Days 6 and 7 postcoitum.