The passage of spermatozoa through the genital tract of female rabbits after ovariectomy and oestrogen treatment.

Abstract

SUMMARY The effect of oestrogen on the passage of spermatozoa through the female genital tract was studied in seventy-nine ovariectomized rabbits. Sexually mature females were spayed, and 1 month later treated for 5–18 days with daily injections of a known quantity of oestradiol benzoate. The does were then mated or surgically inseminated into the vagina or uterus. Twelve to 21 hr later, freshly ovulated ova from unmated donor rabbits were injected into the uterine tubes in order to detect the presence of spermatozoa at the site of fertilization. Ten to 78 hr later the does were killed and the ova recovered and examined for fertilization and the presence of spermatozoa. The proportion of animals with fertilized ova, and the proportion of ova fertilized in individual does, was small before treatment with oestradiol benzoate, but increased after treatment, about 1 μg/day for 4 days giving the best response. Mucus was abundant in the cervices of does injected with 1 μg or more of oestrogen/day. The minimal effective dose of oestrogen was reduced in does which were inseminated into the cervical end of the uterus, and was still lower in does inseminated into the tubal end. This indicates that both the cervix and the uterus restrict the number of spermatozoa reaching the site of fertilization. The restriction can be partially or wholly overcome by oestrogen treatment. Normal mating behaviour can be re-established in ovariectomized does by the daily administration of 1 μg oestradiol benzoate for 4 days.