Nitric Oxide Synthesis by Cultured Endothelial Cells Is Modulated by Flow Conditions

Abstract

In the present study, we examined the hypothesis that dynamic characteristics of flow modulate the production of vasoactive mediators, namely nitric oxide (NO) and endothelin-1 (ET-1), by human umbilical vein endothelial cells (HUVECs). Cells were exposed for 6 hours in a cone-and-plate apparatus to different types of flow: steady laminar, with shear stresses of 2, 8, and 12 dyne/cm2, pulsatile laminar, with shear stress from 8.2 to 16.6 dyne/cm2 and a frequency of 2 Hz; periodic laminar, with square wave cycles of 15 minutes and shear stress from 2 to 8 dyne/cm2, and turbulent, with shear stress of 8 dyne/cm2 on average. A second culture dish was kept in a normal incubator as a static control for each experiment. Laminar flow induced synthesis of NO by HUVECs that was dependent on shear-stress magnitude. Laminar shear stress at 8 dyne/cm2 also upregulated the level of NO synthase mRNA. As observed with steady laminar flow, pulsatile flow also induced an increase in NO release by endothelial cells. When HUVECs were subjected to step-change increases of laminar shear, a further increase of NO synthesis was observed, compared with steady laminar shear of the same magnitude. Turbulent flow did not upregulate NO synthase mRNA or increase NO release. Both laminar and turbulent shear stress reduced, although not significantly, ET-1 mRNA and ET-1 production compared with the static condition. These results indicate that local blood flow conditions modulate the production of vasoactive substances by endothelial cells. This may affect vascular cell functions such as nonthrombogenicity, regulation of blood flow, and vascular tone.

Nitric Oxide Metabolism in Erythropoietin-Induced Hypertension

“…This was inevitably accompanied by a marked rise in blood viscosity, volume expansion, and increased shear stress, which can upregulate vascular and renal NOS expression. [21][22][23][24] These factors were clearly absent in our CRF group treated with EPO alone. Similarly, the goal of EPO replacement in patients with renal disease is the amelioration of CRF anemia as opposed to the induction of erythrocytosis.…”

NO: an inhibitor of cell death

“…In cultured endothelial cells, laminar shear stress not only stimulated NO production but also eNOS expression. 25,26 Shear stress protected human umbilical venous endothelial cells from apoptosis induced by TNFa, 27,28 oxidative stress 28,29 or oxidized LDL 28 in culture, an effect that was partially blocked by L-NMMA. NO donors SNAP and sodium nitroprusside (SNP) further inhibited both TNFa and H 2 O 2 -induced apoptosis in these studies.…”

Use of Ultrasound for Non-Invasive Assessment of Flow-Mediated Dilation

“…In vitro studies suggest that these two distinct fluid stimuli (velocity acceleration vs. steady shear) regulate short-and longterm endothelial function via independent biomechanical pathways 70,71,[73][74][75] . Studies have shown that the rate of velocity acceleration can affect the progression of atherosclerosis 70,73,76) , endothelial cell function 71 , 74) , mechanotransduction 77,78) , calcium kinetics 79,80) , and vascular tone 81,82) . Conditions which affect velocity acceleration include ventricular ischemia 83) , acute myocardial infarction 84) , stenosis 85) , hypertension 86) , and hyperthyroidism 87) .…”