Fluid shear stress increases nitric oxide (NO) production by cultured human aortic smooth muscle cells (hASMC)

We have previously shown that fluid shear stress reduces growth of hASMC in vitro (FASEB ) 9:A588,1995). Since low levels of NO have been shown to inhibit proliferation of cultured SMC, we examined the role of fluid shear stress on release of NO by hASMC. Early passaged hASMC were subjected to physiological levels of shear stress (5, 15, and 25 dyn/cm2) using a parallel plate flow chamber. Conditioned media samples were collected at different time points and nitrite concentration was measured as an index of NO production with colorometric or fluorometric assays. Fluid flow significantly increased NO production in a shear-stress and time-dependent manner. 25 dyn/cm2 for 24 h increased NO production to 153±57 nmole/10⁶ cells compared to stationary culture levels of 6±2 nmole/106 cells (n=7). An initial burst in NO production rate by the initiation of fluid flow (18 nmole/h/10⁶ cells after 2 h of flow) was followed by a gradual decrease with continued exposure to 25 dyn/cm² (6 nmole/h/10⁶ cells after 24 h). Using a fluorometric DAN assay, N-amino-L-arginine, a selective inhibitor of the constitutive isoform of NO synthase, prevented shear stress-induced NO production. These results suggest that fluid shear stress can stimulate NO production by hASMC. This work is supported by Texas Biotechnology Corporation, NIH grants HL18672 and NS23326, Welch Foundation C-0938 and TATP grant 003604.