Circulatory responses to systemic infusions of estrone and estradiol-17α in nonpregnant, oophorectomized ewes

Uterine arterial blood flow dose-response curves to systemic infusions of either estrone (E₁) or estradiol-17α (E_2α) were determined in ten oophorectomized, nonpregnant ewes. Maximum uterine blood flow occurred with 5 μg per kilogram of E₁ and ≥ 20 μg per kilogram of E_2α. Total uterine blood flow measured with isotope-labeled microspheres rose more than tenfold following 30 μg per kilogram of either estrogen, as did blood flow to the myometrium, endometrium, and uterine caruncles (p < 0.05). Distribution of uterine blood flow was unaltered. Cervical and vaginal blood flows increased ten-to twenty-fold with E₁ and E_2α, while mammary gland blood flow rose 54 and 77 per cent. Significant increases in adrenal and thyroid blood flows were documented. The only significant decrease in blood flow occurred in the pancreas (- 13 per cent; p < 0.05) following E_2α infusion. At the dose studied, E₁ and E_2α are potent vasodilators of reproductive tissues, especially the cervix and vagina. As they appear to be the major estrogens during ovine pregnancy, it is likely they participate in the preparation of these tissues for parturition.