FURTHER OBSERVATIONS ON THE EFFECTS OF OESTRADIOL ON TUBAL EGGS AND IMPLANTATION IN THE GUINEA-PIG

Abstract

In guinea-pigs, low doses of oestradiol benzoate, given immediately after mating, inhibit pregnancy. This is not due to retention of eggs in the Fallopian tubes but to their expulsion. It is suggested on present evidence that the term "tube-locking" should be dropped, unless it is clearly shown that eggs are detained in the Fallopian tubes beyond the usual period. Once the fertilized eggs have passed normally into the uterus, implantation is not prevented by as much as 30 or 50 [mu]g estradiol in the guinea-pig, but later stages of development may be affected and the corpora lutea regress completely, either because of a failure of the placental luteotrophic hormone at about 10 days post coitum (p.c.) or through a direct effect of estrogen on the secretion of pituitary gonadotrophins. In animals which aborted or resorbed their embryos, estrus returned about Day 16. Implantation was not inhibited by 20 [mu]g estradiol in guinea-pigs ovariectomized on Day 5 and injected on Days 6 and 7 p.c.