Uterine arterial vasoconstrictions mediated by ovarian nerves in virgin and postpartum rats

In most mammals, including humans, pregnancy results in the loss of most uterine vasomotor fibers. These experiments determined whether, despite this denervation, sympathetic nerves mediated uterine vasoconstrictions in the rat 24 h after delivery. Both virgin and uniparous postpartum rats were anesthetized with urethan. Femoral vessels were cannulated for measurement of arterial pressure and intravenous administration of fluids and drugs. Blood flow was measured in a uterine artery after ligation of all anastomotic ovarian vessels. Electrical stimulation of ovarian nerve efferents elicited frequency-dependent uterine vasoconstrictions in both virgin and postpartum rats. Vasoconstrictions in postpartum rats were not significantly different from those observed in virgins. In both virgin and postpartum rats, neurogenic vasoconstrictions were reduced by combined α₁- and α₂- adrenergic blockade. We conclude that the uterine branches of the ovarian nerve mediate adrenergic uterine vasoconstrictions. In the largely denervated uterus of the postpartum rat, these vasoconstrictions may be mediated by surviving innervation of the uterine artery and its major branches. Sympathetic vasoconstriction acting at these sites would constitute an effective defense against postpartum hemorrhage.