lschemic acute kidney injury (AKI} results in both tubular injury and red blood cell (RBC) congestion in the renal medulla. RBC congestion of medullary capillaries leads to prolonged hypoxia and long-term ischemia in the renal medulla. Much evidence suggests that medullary ischemia and vascular rarefaction promotes the development of hypertension. Further, hypertension may drive glomerular injury and chronic kidney disease (CKD) following nephron loss. Our goal is to better understand the mechanisms by which renal medullary RBC congestion can be experimentally prevented and whether RBC congestion drives the long-term sequelae of ischemic AKI. As such, Aim 1 will test whether prevention of renal medullary RBC congestion prevents development of hypertension and CKD following ischemic AKI utilizing gold-standard techniques to assess renal function and microvascular rarefaction, including telemetry, microphil infusion, and small animal micro CT. The results from this aim will help to better delineate the contribution of the initial tubular injury resulting from ischemia-reperfusion {IR} within 24h of ischemia, versus the contribution of RBC congestion and prolonged medullary ischemia {days), to the development of hypertension and CKD. Our novel preliminary data indicate that pre-treatment with low doses of lipopolysaccharide (LPS) completely prevents RBC congestion in the peritubular capillaries following IR, independent of the initial level of tubular injury. lmmunohistological analysis of the first 24 hours following reperfusion revels that RBC congestion originates in the ascending vasa recta (VR) during the ischemic period. Further, rapid-reperfusion of the VR which drain the renal medulla upon reperfusion, occurs only in LPS treated rats, which then prevents peritubular congestion. VR are densely surrounded by contractile pericytes, and NO has been shown to limit pericyte constriction. Upregulation of iNOS in VR may protect the kidney from subsequent ischemia by reducing VR resistance, promoting rapid reperfusion of these important vessels, and thereby preventing peritubular congestion. Aim 2 will test whether low dose LPS promotes increases in iNOS-mediated nitric oxide production in medullary VR. These aims test our central hypothesis that preconditioning with low dose LPS results in rapid reperfusion of the medullary VR due to increased VR iNOS activity and nitric oxide production and that this will prevent peritubular capillary congestion, greatly improve recovery of renal function, and prevent the subsequent development of hypertension and CKD following IR. The proposed study will establish the significance of RBC congestion in the medulla to drive long-term ischemic injury and complications, with hope that understanding the mechanisms by which we prevent congestion, may provide much needed novel therapeutic approaches. My strong preliminary data, experienced mentor team, and rigorous training plan ensure this proposal has a high likelihood...