Blood Flow Regulates the Development of Vascular Hypertrophy, Smooth Muscle Cell Proliferation, and Endothelial Cell Nitric Oxide Synthase in Hypertension

Blood flow participates in vascular remodeling during development and growth by regulating cell apoptosis and proliferation. However, its significance in the development of vascular hypertrophy and vascular remodeling in hypertensive patients is not known. We investigated how changing blood flow through the common carotid artery (CA) of young adult rats rendered hypertensive via aortic coarctation affects CA hypertrophy and/or remodeling responses to hypertension. Blood flow was reduced by approximately 50% as a result of ligation of the external CA immediately after hypertension was induced, and the effects of that procedure were compared with those in similarly treated normotensive rats. Reducing blood flow in the hypertensive animals markedly augmented the development of CA hypertrophy over the ensuing 14 days by increasing the vessel wall cross-sectional area. In those animals, CA lumen size was unaltered by reducing blood flow, as was CA structure in normotensive animals. The greater hypertrophy in the hypertensive animals with reduced blood flow was associated with enhanced smooth muscle cell (SMC) proliferation 3 days after the hemodynamic changes were induced. There also appeared to be more extensive remodeling of the endothelium in the hypertensive animals with normal flow; this was indicated by the greater frequency of apoptotic endothelial cells at that time. This reduction in blood flow also attenuated endothelial cell nitric oxide synthase expression in hypertensive animals but not in normotensive animals. Severe reductions in blood flow ( approximately 90%) were required to reduce endothelial cell nitric oxide synthase in the normotensive animals. Increasing CA nitric oxide levels by perivascular application of S-nitroso-N-acetylpenicillamine (SNAP) to the CAs of hypertensive animals with reduced endothelial cell nitric oxide synthase attenuated the greater SMC proliferation. Thus, reduced blood flow in hypertensive animals promotes hypertrophy by enhancing SMC proliferation via mechanisms that reduce the inhibitory effects of nitric oxide on SMC proliferation.