Emerging evidence indicates that oxidative stress, a state of excessive reactive oxygen species (ROS) activity, is associated with cardiovascular diseases, such as hypertension. ROS, including superoxide and H202, have been implicated in several key events in the early process of hypertension and medial hypertrophy. The NADPH oxidase system of vascular cells, whose central component is Nox1, is the major source of ROS in vascular tissues. The Rho family GTP triphosphatase Rac1 is a key activator of NADPH oxidase, leading to the production of ROS, including superoxide and H202. We have engineered a transgenic mouse model that overexpresses the constitutively activated mutant of the human Rac1 protein in the smooth muscle cells in FVB/N mice (Rac-CA), using mouse smooth muscle a-actin promoter. The arterial vessels of these Rac-CA mice exhibit impaired vasodilatory activity of nitric oxide (NO), enhanced expression of superoxide dismutase (SOD) isoforms, indicative of superoxide activity, and a marked increase in H202 level. In addition, these mice develop hypertension that is mediated via a ROS-dependent, but angiotensin/renin-independent pathway, as the constitutively active state of the Rac1 transgene product does not require signaling reactions upstream of Rac (angiotensin receptor-1 engagement, CED-5IDockl 80, etc.). Our central hypothesis is that overproduction of superoxide by NADPH oxidase in response to Rac1 activation within the arterial vessel wall, antagonizes the vasodilatory effects of nitric oxide, resulting in hypertension and arterial media hypertrophy. We propose to characterize the molecular events associated with Rac-CA overexpression in the vessel wall leading to the observed phenotype. We will study the contribution of ROS to the development of hypertension and arterial media hypertrophy in Rac-CA mice in various genetic backgrounds (FVB/N and C57BL/6). Furthermore, through the use of strategic crosses between Rac-CA mice and other established models, we will study the role of NADPH oxidase, the manganese type superoxide dismutase, catalase and glutathione peroxidase in hypertension and vascular hypertrophy. The use of potent inhibitors will complement our work with transgenic/knockout mice, and provide further proof of concept to the role of Rac1 and resultant ROS in hypertension and arterial media hypertrophy. This program should substantially improve our understanding of the role of superoxide and derived ROS in the control of blood pressure homeostasis. Novel targets for therapeutic strategies will ensue, and mouse models created in the context of this program will be invaluable to many investigators in this field of research