Cyclic strain increases endothelial nitric oxide synthase activity.

BACKGROUND: Endothelial nitric oxide synthase (eNOS) is an important enzyme that controls the production of a potent vascular smooth muscle relaxing factor, nitric oxide. However, the role of hemodynamic forces (blood pressure, cyclic strain, and shear stress) on the regulation of eNOS has not been fully elucidated. Recently, we showed that cyclic strain increases eNOS gene and protein in cultured bovine aortic endothelial cells (EC). Because an increase in gene transcription and protein synthesis may not necessarily translate into an increase in functional activity, the aim of this study was to determine the effects of cyclic strain on eNOS activity.
METHODS: EC were seeded onto plates with flexible bottoms that can be deformed by vacuum and were then exposed to 60 cycles/minute of either 24% maximum strain (-20 kPa vacuum) or 10% maximum strain (-5 kPa vacuum) for 24 hours. eNOS activity was assessed, and nitric oxide production was determined (as nitrite) by the Greiss reaction.
RESULTS: Twenty-four percent strain, at 60 cycles/min, but not 10% strain significantly increases eNOS activity compared with stationary controls. Both strain regimens increased nitric oxide (as nitrite) in culture media compared with stationary controls, although nitrite in media of EC exposed to high strain were significantly increased compared with the lower strain.
CONCLUSIONS: Cyclic strain increases eNOS activity in cultured bovine aortic EC. These results may indicate the importance of hemodynamic forces in the regulation of eNOS in vivo.