Neurovascular mechanisms of hypertension in pregnancy

Normal pregnancy is associated with significant changes in the neuronal and vascular control mechanisms of blood pressure (BP). Preeclampsia (PE) is a major complication of pregnancy characterized by proteinuria, and increased vascular resistance and BP. If untreated, PE leads to eclampsia with serious seizures and severe hypertension. However, the neurovascular mechanisms of hypertension in pregnancy and PE are unclear. Studies in animal models of hypertension in pregnancy suggest that inadequate cytotrophoblast invasion of uterine spiral arteries causes reduction in uteroplacental perfusion pressure leading to placental ischemia/hypoxia. Placental ischemia may promote the release of biologically active factors such as cytokines and reactive oxygen species. These circulating factors may increase the vascular permeability, cross the blood-brain barrier, and affect the sympathetic tone and the neuronal control mechanisms of BP. Placental factors could also cause endothelial cell dysfunction and inhibit nitric oxide (NO)-cyclic guanosine monophosphate (cGMP), prostacyclin (PGI(2))-cyclic adenosine monophosphate (cAMP), and hyperpolarizing factor vascular relaxation pathways. Additionally, placental factors may induce endothelium-derived contracting factors such as endothelin, thromboxane and angiotensin II, which stimulate Ca(2+)-dependent vascular smooth muscle (VSM) contraction or increase protein kinase C activity and enhance myofilament sensitivity to intracellular free calcium concentration ([Ca(2+)](i)). The increased sympathetic tone combined with systemic decrease in endothelium-dependent vascular relaxation and enhanced VSM contraction may contribute to the increased vascular resistance and BP associated with PE. The hypertensive state in severe PE may weaken the blood-brain barrier and precipitate convulsions and cerebral hemorrhage. Careful monitoring of maternal neuronal, endothelial, and VSM function during pregnancy should circumvent the life-threatening neurovascular complications of PE-eclampsia.