Spiral arterial remodeling is not essential for normal blood pressure regulation in pregnant mice.

ABSTRACT

Maternal cardiovascular adaptations occur in normal pregnancy, systemically, and within the uterus. In humans, gestational control of blood pressure is clinically important. Transient structural remodeling of endometrial spiral arteries normally occurs in human and mouse pregnancies. In mice, this depends on uterine natural killer cell function. Using normal and immune-deficient mice, we asked whether spiral artery remodeling critically regulates gestational mean arterial pressure and/or placental growth. Radiotelemetric transmitters were implanted in females and hemodynamic profiles to a dietary salt challenge and to pregnancy were assessed. Implantation sites from noninstrumented females were used for histological morphometry. Both normal and immune-deficient mice had normal sensitivity to salt and showed similar 5-phase gestational patterns of mean arterial pressure correlating with stages of placental development, regardless of spiral artery modification. After implantation, mean arterial pressure declined during the preplacental phase to reach a midgestation nadir. With gestation day 9 opening of placental circulation, pressure rose, reaching baseline before parturition, whereas heart rate dropped. Heart rate stabilized before parturition. Placental sizes deviated during late gestation when growth stopped in normal mice but continued in immune-deficient mice. As an indication of the potential for abnormal hemodynamics, 2 pregnant females delivering dead offspring developed late gestational hypertension. This study characterizes a dynamic pattern of blood pressure over mouse pregnancy that parallels human gestation. Unexpectedly, these data reveal that spiral artery remodeling is not required for normal gestational control of blood pressure or for normal placental growth.