Phase angle between circumferential strain and wall shear stress affects endothelial cell biochemical production

Simultaneous fluid wall shear stress (WSS) and circumferential strain (CS) can alter endothelial cell (EC) biological responses and regulate vascular function. The stress phase angle (SPA) between CS and WSS, which characterizes the dynamic force pattern applied on ECs, is believed to be important in determining EC biological response. A pulsatile flow loop containing elastic (Sylgard) tubing, with bovine aortic ECs (BAECs) precultured inside, was developed in order to expose the EC layer to simultaneous oscillatory WSS (10±10 dyn/cm² ) and CS (8%). By adjusting elastic components in the flow loop, a range of SPA between +12°(in phase) and -105°(off phase) could be obtained while maintaining stress levels the same. Different stress conditions were run, including steady WSS, oscillatory WSS without CS, simultaneous oscillatory WSS and CS with +12° and -105° SPA. Four hour experiments indicate that steady WSS induces EC to release significant prostacyclin (PGI2) and nitric oxide (NO) while oscillatory WSS induces only 12% of steady PGI2 production and 42% of steady NO production. Oscillatory WSS and CS with positive SPA induce 40% of steady PGI2 production and 53% of steady NO production; while with negative SPA, 11% of steady PGI2 production and 50% of steady NO production are observed