Endothelial cells are exposed to mechanical stimuli from blood flow and blood pressure. However, it is not yet fully understood how their simultaneous exposure affects endothelial function. Firstly, in this study we investigated the effect of combined stress on morphology of cultured human aortic endothelial cells (HAECs). In the results, HAECs exposed to steady flow (1. 5 Pa, 100 mmHg) were more elongated than those exposed to hydrostatic pressure (100 mmHg) and HAECs exposed to pulsatile flow

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... 1 (1.2 1.8 Pa, 80 120 mmHg) were more elongated than those exposed to steady flow. Similarly, HAECs exposed to pulsatile flow 1 were most oriented to the flow direction among these three stresses. Secondly, we investigated the effect of combined stress on gene expression of cell adhesion molecules in HAECs. After stress exposure to HAECs the mRNA of intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1) and E-selectin were measured by real time RT-PCR. In the results, the exposure of steady flow increased the mRNA levels of ICAM-1 compared to the exposure of hydrostatic pressure, however, the exposure of pulsatile flow 1 decreased the mRNA level of ICAM-1 compared to the exposure of steady flow. Moreover, the exposure of pulsatile flow 2 (1.2 1.8 Pa, 180 220 mmHg) increased mRNA levels of ICAM-1, VCAM-1 and E-selectin compared to the exposure of pulsatile flow 1. These findings suggest that gene expression of cell adhesion molecules induced by combined stress were different to the superposition of individual stress and that not only difference in the components of combined stress but also difference in the magnitude of the components of combined stress are important.