Corticosteroid suppression of estrogen-induced uterine blood flow in nonpregnant sheep.

Estrogenic stimulation of uterine hyperemia and water imbibition are well-described endocrine events. Uterine blood flow responses to estrogen appear to have a similar mechanism of action. Although corticosteroids inhibit the uterine hyperemic and water imbibition effects, their influence on estrogen-induced uterine blood flow has not been clarified. Accordingly, the effects of hydrocortisone on estrogen-induced uterine blood flow were studied in seven nonpregnant castrate ewes equipped with electromagnetic flow probes around the main uterine arteries and with polyvinyl catheters inserted into postbifurcational branches of the uterine arteries. Inferior vena cava infusions of hydrocortisone, 0.50 to 9.25 mg/kg of body weight, administered 1 hour before estrogenic stimulation suppressed uterine blood flow increases by 10% to 35%. Direct uterine intra-arterial infusions of hydrocortisone also inhibited estrogen-induced uterine blood flow at calculated concentrations as low as 5.65 microM in uterine arterial blood. These findings support the conclusion that estrogen-induced uterine blood flow and water imbibition are correlative events and further serve to elucidate the mechanisms by which steroid hormones interact to modify uterine blood flow.