Abstract INTRODUCTION AND OBJECTIVE: Obstructive uropathy is a major clinical problem that can result in permanent renal damage. The renoprotective effect of direct renin inhibitor (aliskiren) has been demonstrated in many experimental animal models mainly renal ischemia/reperfusion injury. Therefore, we studied the effect of aliskiren on the renal function during acute and chronic partial ureteral obstruction (PUO) in rat solitary kidney. METHODS: 60 male Sprague–Dawley rats were randomly allocated into 3 groups (20 rats each); sham, PUO and aliskiren groups. Right nephrectomy was performed in all groups. Rats in PUO and aliskiren groups were subjected to left PUO and received no treatment and aliskiren (10 mg/kg, orally, once per day till sacrification), respectively. Blood samples were then collected for biochemical measurements. 10 rats from each group were sacrificed after 2 weeks, while the remaining rats were sacrificed after 4 weeks. Left kidneys were harvested for histopathological examination, BCL-2, IL-6, TGF-β1, collagen I and fibronectin relative gene expression and assessment of glutathione (GSH), superoxide dismutase (SOD), malondialdehyde (MDA) and nitric oxide (NO) activity. RESULTS: After 2 and 4 weeks of PUO, aliskiren significantly recompensed the rise of serum creatinine (Scr) and blood urea nitrogen (BUN). Aliskiren also revealed significantly better histopathological results regarding cortical and medullary necrosis, regeneration and inflammatory cell infiltration (table 1). Aliskiren group showed significant up-regulation of BCL-2 and down-regulation of IL-6, TGF-β1, collagen I and fibronectin gene expression (table 2). Aliskiren also significantly increased GSH and SOD activity and reduced MDA and NO activity (table 2). Moreover, aliskiren administration for 4 weeks after PUO significantly yielded more renoprotective effect compared to its administration for 2 weeks. CONCLUSIONS: Aliskiren ameliorates the deterioration of the renal function during acute and chronic PUO in a solitary kidney.