Which of the following statements about the role of the endothelium is/are correct?

B. Endothelial cell–derived nitric oxide (NO) is produced by a constitutive and an inducible NO synthase

D. A local renin-angiotensin system is found in the walls of arteries and veins.

DISCUSSION: Endothelial cells have the ability to mediate both contractile (prostanoids, oxygen free radicals, endothelins, angiotensins, and uncharacterized endothelium-derived constriction factors) and relaxant (prostanoids, nitric oxide and nitric oxide–containing compounds, hyperpolarization factor) responses. NO is synthesized from the conversion of Larginine to citrulline by at least two categories of enzymes— constitutive nitric oxide synthases (cNOS, predominantly membrane bound) and inducible nitric oxide synthases (iNOS, predominantly cytosolic), both of which are calcium- and calmodulin dependent. Constitutive NOS is present in endothelial cells, and following cytokine stimulation endothelial cells also synthesize iNOS. In addition to its basic barrier function, the endothelium regulates intravascular coagulation by three other separate, but related, mechanisms: participation in procoagulant pathways, inhibition of procoagulant proteins, regulation of fibrinolysis and production of thromboregulating compounds. There is a local renin-angiotensin system in the vessel wall of both vein and arteries, and this system is considered important in the maintenance of blood pressure, the control of hypertension, and the response of the vessel wall to injury. In contrast to the macrocirculation, the microcirculation has distinctive vasomotor characteristics. Vessels of the microcirculation are the conduits that are responsible for the local delivery and transfer of cell substrates and metabolites. The endothelium regulates the microvasculature, reacting to the metabolic needs of tissue; it is essential in organ autoregulation and in the responses of these microvasculatures to changes in local blood flow. Reactive hyperemia appears to be dependent on the immediate  production of endothelium-derived cyclo-oxygenase products, predominantly prostaglandin E 2 (PGE 2), as opposed to PGI 2, in the short term.