HORMONAL REQUIREMENTS FOR THE MAINTENANCE OF OESTRADIOL-INDUCED INHIBITION OF UTERINE SENSITIVITY IN THE OVARIECTOMIZED RAT

Abstract

SUMMARY Ovariectomized rats treated with 2·5 or 5·0 mg. progesterone daily received a single subcutaneous injection of 0·2 μg. oestradiol on the third day of the progesterone treatment. The deciduomal response to trauma by endometrial scratching was used to determine the degree of uterine sensitivity at various times after oestradiol. Uterine sensitivity was partially and then completely lost 36 and 48 hr. after oestradiol administration. The inhibition of uterine sensitivity persisted until 9 and 11 days after oestradiol when the animals received 2·5 and 5·0 mg. progesterone daily. Uterine sensitivity was completely inhibited on day 11 with doses of oestradiol from 0·2 to 0·05 μg. Withdrawal of progesterone treatment for 48 or 72 hr., but not for 24 hr., after oestradiol treatment restored uterine sensitivity. These results show that the oestradiol-induced inhibition of uterine sensitivity in the progestational endometrium is maintained by continuous progesterone treatment and that the duration of this effect is dependent on the dose of progesterone given.