Responses of reproductive and nonreproductive tissues to 17β-estradiol during ovine puerperium

The responses of regional blood flows and cardiac output to the systemic infusion of 17β-estradiol (E₂) (1μg/kg) were studied with radionuclide-labeled miscrospheres in 11 chronically instrumented ewes 1-12 days after lambing. Blood flow to the uterine myometrium, endometrium, and caruncles increased 818 ± 212, 1,149 ± 376, and 544 ± 160% (mean ± SE, P<0.025), respectively, within 90 min after the infusion of E₂. There was, however, in each of these tissues a progressive increase in the magnitude of the response to E₂ stimulation as the puerperium progressed, not attaining changes expected in the prepregnant ewe until the 12th postpartum day. Significant vasodilation also occurred in the fallopian tubes, cervix, vagina, ovaries, mammary gland, skin, and thyroid gland. The magnitude of the blood flow response in the tubes, cervix, and vagina increased as the puerperium progressed. Cardiac output rose 17 ± 10% (P<0.05) after the infusion of E₂. Although the ovine reproductive tissues are sensitive to estrogen-induced vasodilation throughout the puerperium, the magnitude of the responses progressively increase, suggesting that vascular reactivity in these tissues is changing and is not similar to that of the prepregnant animal.