CONSTITUTIVE NOS EXPRESSION IN CULTURED ENDOTHELIAL-CELLS IS ELEVATEDBY FLUID SHEAR-STRESS

The role of chronic fluid shear stress on endothelial constitutive nit ric oxide synthase (cNOS) levels may have an important role in vessel diameter control. We subjected primary human umbilical vein endothelia l cells (HUVEC) or bovine aortic endothelial cells (BAEC, passages 2-1 4) to steady laminar shear stress. In both cell types, the intracellul ar level of cNOS was elevated within 3 h of flow exposure at 25 dyn/cm (2) and remained elevated at 6 and 12 h of flow exposure, compared wit h stationary controls, as indicated by digital immunofluorescence micr oscopy. Shear stress exposure for 6 h caused a 2.2 +/- 0.3- and 2.8 +/ - 0.3-fold elevation of cNOS protein levels in BAEC (n = 3, P < 0.01) and HUVEC (n = 3, P < 0.01), respectively, in the presence or absence of 1 mu M dexamethasone. Dexamethasone suppresses induction of the ind ucible NOS gene, indicating that cNOS was elevated by fluid shear stre ss. Flow exposure at 4 dyn/cm(2) caused no enhancement of cNOS levels in either cell type. The flow induction of the cNOS protein levels was not blocked by preincubation of BAEC with 100-400 mu M Of N-G-nitro-L -arginine methyl ester, indicating that flow-induced NO (or guanosine 3',5'-cyclic monophosphate) was not involved in the elevation of cNOS levels. Protein kinase C inhibitor H-7 (10 mu M) had no effect on indu ction of NOS protein in BAEC exposed to 25 dyn/cm(2). The cNOS mRNA le vels were found to be elevated by two- to threefold in BAEC after 6 or 12 h of flow exposure at either 4 or 25 dyn/cm(2), and this induction of NOS mRNA occurred in the presence of dexamethasone. The elevation of cNOS levels by chronic flow exposure may provide a mechanism for ch ronic regulation of vessel diameter by endothelial response to prevail ing blood flow.