Reactivities of the nongravid uterine vasculatures: effects of norepinephrine.

Responses of the component tissues of the nonpregnant ovine uterus to intravenous administration of norepinephrine were determined with radioactively labeled microspheres under flowmeter guidance. During a mean decrease in uterine conductance to 42 per cent of control, no significant differences in the distribution of uterine blood flow to caruncles, endometrium, myometrium, or cervix occurred. These observations differ from those during the last half of gestation, when placental vascular reactivity to norepinephrine is muted. They support the concept that fundamental changes in placental vascular responses occur during placentation.