Endothelial cells produce cyclooxygenase- dependent vasoconstrictor substances, such as prostanoids and oxygen free radicals. Cyclooxygenase- dependent endothelium-derived contracting factors (EDCFs) were at first identified as responsible for impaired endothelium-dependent vasodilation in patients with essential hypertension. However, production of EDCFs is a phenomenon specific to aging, with essential hypertension merely causing an earlier onset and worsening of this alteration. Furthermore, both in aging and in hypertension, the appearance of cyclooxygenase-derived contracting factors is associated with a parallel decrease in nitric oxide (NO) availability, suggesting that these substances could be oxygen free radicals. Other clinical conditions characterized by production of cyclooxygenase-dependent EDCFs are acute estrogen deprivation and heart failure. By reducing NO availability, EDCFs could conceivably act as promoters of atherosclerosis and cardiovascular events...