ABSTRACT
The pulmonary vascular endothelium plays a key role in the dynamic regulation of vascular tone. Endothelial cells (ECs) continuously transduce numerous physiological signals received by the lung and make appropriate changes to pulmonary vascular resistance (PVR). The most dramatic changes in the pulmonary vascular tone occur during birth-related transition. Endothelium plays a prominent role in the rapid decrease in PVR that occurs at birth by sensing changes in oxygen tension, shear stress, and release of vasoactive mediators, such as vascular endothelial growth factor and adenosine triphosphate. ECs, in turn, send vasodilator signals, such as nitric oxide and prostacyclin, to vascular smooth muscle cells to initiate vasodilation. Hypoxic stress can delay and/or abolish this transition at birth, in part, by impairing endothelial function. The three basic mechanisms by which pulmonary vascular tone increases in response to hypoxia include: vasoconstriction in response to acute hypoxia, remodeling of the vessel wall in response to sustained hypoxia and decreased capillary angiogenesis in response to long-term hypoxia. ECs play an essential role in these processes, as reviewed in this chapter.
