Regulation of the lung capillary
At least three regulatory mechanisms are involved in lung capillary vasoconstriction and dilation. The prostacyclin pathway
Prostacyclin (PGI2) is a vasodilator and antiproliferative molecule which is produced by the action of prostacyclin synthase on arachidonic acid in endothelial cells. It has its effect by acting on the cAMP pathway in vascular smooth muscle cells. The nitric oxide pathway
Nitric oxide (NO) is also a vasodilator and antiproliferative molecule produced in endothelial cells
from arginine by NO synthase. It acts by stimulating the production of cGMP in vascular smooth muscle cells and thereby vasodilation. See also the vascular nitric oxide regulation in the cardiology chapter. The endothelin pathway
Endothelin (ET-1) is a vasoconstrictor and promoter of cell proliferation and is produced from pre-pro-endothelin in endothelial cells. It acts via the two receptors (ETA and ETB) present on vascular smooth muscle cells mediating proliferation and vasoconstriction.