V1R and V2R and vasopressin receptors. ET-A and ET-B are endothelin receptors, α1, α2, β1 and β2 are adrenergic receptors. PLC – phospholipase C, IP3 – inositol triphosphate; eNOS – endothelial nitric oxide synthase, NO – nitric oxide, sGC – soluble guanylyl cyclase, PDE3 – phosphodiesterase 3. Most of the vasoconstrictor mediators result in increase in cytosolic ionic calcium concentrations in the smooth muscle. Vasopressin (through V1 receptors), endothelin (through ET-B receptors) and norepinephrine (through α2 receptors) can act on pulmonary endothelium and stimulate NO production leading to pulmonary vasodilation. Copyright Satyan Lakshminrusimha.