Study objective: Endothelium derived nitric oxide (NO) is an important modulator of resting vascular tone. The aim of the study was to investigate the extent by which the rate of NO release is modulated by the two determinants of vascular conductance: pressure and flow. DESIGN AND EXPERIMENTAL MATERIAL: Porcine macrovascular endothelial cells cultured on microcarrier beads were used as a model in which the rate of NO release was determined photometrically. Columns packed with endothelial cell covered beads were perfused at different flow rates (2, 10, 20 ml.min-1) and perfusion pressures (ranging from 6 to 200 mm Hg).
Measurements and main results: Release of endothelial cell derived NO was continuously quantified under basal and ATP stimulated conditions using a specific difference spectrophotometric assay. Increasing flow flow from 2 to 20 ml.min-1 enhanced the basal NO release from endothelial cells fivefold. ATP (10(-4) M) augmented the NO release from endothelial cells more than 10-fold at each flow level studied. The ATP induced NO release rapidly increased by a factor of 5.8 when flow was enhanced from 2 to 20 ml.min-1 (greater than 180 pmol.min-1.mg endothelial cell protein). Raising perfusion pressure from 6 to 200 mm Hg in endothelial cells did not affect the rate of basal NO release.
Conclusions: (1) The rate of NO release from endothelial cells increases when flow is enhanced. (2) Endothelial cells possess a high capacity for NO production, permitting a rapid adjustment of NO release to changes in flow. (3) The rate of NO release is not causally related to changes in perfusion pressure.