Activation of the renin-angiotensin-aldosterone system (RAAS) has been associated with risk of ischemic cardiovascular events, while interruption of the RAAS by ACE inhibition reduces cardiovascular mortality. We have previously proposed that a major component of the vascular toxicity associated with activation of the RAAS derives from effects of angiotensin II (Ang II) on fibrinolytic balance. Ang II stimulates expression of plasminogen activator inhibitor-1 (PAI-1) both in vitro and in humans. PAI-1 if the major physiological inhibitor of fibrinolysis and increased PAI-1 expression occurs in atherosclerotic plaques and nephrosclerotic glomeruli. Emerging data suggest that aldosterone plays a role, independent of Ang II, in vascular toxicity, myocardial fibrosis, and nephrosclerosis. Moreover, data from the Randomized Aldactone Evaluation Study (RALES) confirm the contribution of aldosterone to cardiovascular mortality in humans. The current proposal is based on preliminary data from our laboratory that suggest that aldosterone, like Ang II, increases expression of PAI-1. Specifically, we have shown that aldosterone increases PAI-1 expression in human cell lines and in vivo in rats, that interruption of the RAAS in salt-deplete humans decreases PAI-1, that PAI-1 concentrations correlate with aldosterone, and that local adrenal venous PAI-1 concentrations are increased in patients with primary hyperaldosteronism. The present proposal tests the hypothesis that aldosterone contributes to the vascular toxicity associated with activation of the RAAS by enhancing the production of PAI-1. We will test this hypothesis by comparing the effects of aldosterone, alone and in combination with Ang II, on end-organ damage in wile-type, PAI-1 and t-PA deficient mice and by determining the effect of a novel PAI-1 inhibitor on Ang II and aldosterone-induced end-organ damage (SPECIFIC AIM 1). Using AT1AR and MR deficient mice, as well as pharmacological tools such as AT1R, AT4R, and MR antagonists, we will examine the mechanism(s0 through which aldosterone enhanced the effects of Ang II on PAI-1 expression. We will test the hypothesis that endogenous aldosterone regulates the fibrinolytic and vasodilator functions of the human endothelium (SPECIFIC AIM 2). We will determine genetic and other factors that modulate the effect of endogenous aldosterone on fibrinolytic balance in humans. This multi-disciplinary approach will generate new information regarding the role of aldosterone in vascular toxicity and, thus, improve our ability to prevent and treat cardiovascular disease.