Shear stress regulation of endothelial NOS in fetal pulmonary arterial endothelial cells involves PKC

We have shown that increased pulmonary blood flow at birth increases the ac tivity and expression of endothelial nitric oxide (NO) synthase (eNOS). How ever, the signal transduction pathway regulating this process is unclear. B ecause protein kinase C (PKC) has been shown to be activated in response to shear stress, we undertook a study to examine its role in mediating shear stress effects on eNOS. Initial experiments demonstrated that PKC activity increased in response to shear stress. NO production in response to shear s tress was found to be biphasic, with an increase in NO release up to 1 h, a plateau phase until 4 h, and another increase between 4 and 8 h. PKC inhib ition reduced the initial rise in NO release by 50% and the second increase by 70%. eNOS mRNA and protein levels were also increased in response to sh ear stress, whereas PKC inhibition prevented this increase. The stimulation of PKC activity with phorbol ester increased eNOS gene expression without increasing NO release. These results suggest that PKC may play different ro les in shear stress-mediated release of NO and increased eNOS gene expressi on.