Characterization of vascular relaxant factor released from cultured endothelial cells.

Cultured bovine endothelial cells were grown on microcarrier beads. Columns (0.2 ml) packed with microcarriers were perfused with oxygenated (20% O2) Tyrode's solution containing indomethacin (10 microM), and the effluent was passed through precontracted, endothelium-denuded detector arteries. When the endothelial cells were stimulated with bradykinin (3-100 nM), adenosine 5'-triphosphate (0.3-30 microM), or calcium ionophore A23187 (10-300 nM), they released dose-dependently a nonprostanoid compound that dilated the detector vessel. The factor, probably identical to the endothelium-derived relaxing factor of native endothelium, evoked dilations of the same magnitude in different types of detector vessels (rabbit thoracic aorta, rabbit femoral artery, canine coronary artery). However, this relaxant factor was significantly more effective in arteries precontracted by norepinephrine or serotonin than in arteries precontracted by potassium depolarization. Thus, its dilator action resembles that of the nitrovasodilators. The factor is labile, with an apparent half-life in the range of 20 to 30 seconds. Its dilator potency was inhibited by dithiothreitol (0.2 mM), metyrapone (0.2 mM), nordihydroguaiaretic acid (20 microM), and hemoglobin (1 microM), all of which apparently inactivated the factor. Synthesis or release (or both) of the relaxant factor was abolished by methylene blue (1 microM). High PO2 levels (greater than 400 mm Hg) in the perfusate markedly reduced the release of the relaxant factor from the cultured cells. This study demonstrates that a vascular relaxant factor is released from endothelial cells in monoculture by adenosine 5'-triphosphate, bradykinin, and A23187 and establishes such a culture as a useful tool for analyzing the mechanisms of endothelium-dependent vasomotion.