Abstract-Afferent arterioles were used to investigate the role of adenosine, angiotensin II, NO, and reactive oxygen species in the pathogenesis of increased tubuloglomerular feedback response in hydronephrosis. Hydronephrosis was induced in wild-type mice, superoxide dismutase-1 overexpressed mice (superoxide-dismutase-1 transgenic), and deficient mice (superoxide dismutase-1 knockout). Isotonic contractions in isolated perfused arterioles and mRNA expression of NO synthase isoforms, adenosine, and angiotensin II receptors were measured. In wild-type mice, N G -nitro-L-arginine methyl ester (L-NAME) did not change the basal arteriolar diameter of hydronephrotic kidneys (Ϫ6%) but reduced it in control (Ϫ12%) and contralateral arterioles (Ϫ43%). Angiotensin II mediated a weaker maximum contraction of hydronephrotic arterioles (Ϫ18%) than in control (Ϫ42%) and contralateral arterioles (Ϫ49%). The maximum adenosine-induced constriction was stronger in hydronephrotic (Ϫ19%) compared with control (Ϫ8%) and contralateral kidneys (Ϯ0%). The response to angiotensin II became stronger in the presence of adenosine in hydronephrotic kidneys and attenuated in contralateral arterioles. L-NAME increased angiotensin II responses of all of the groups but less in hydronephrotic kidneys. The mRNA expression of endothelial NO synthase and inducible NO synthase was upregulated in the hydronephrotic arterioles. No differences were found for adenosine or angiotensin II receptors. In superoxide dismutase-1 transgenic mice, strong but similar L-NAME response (Ϫ40%) was observed for all of the groups. This response was totally abolished in arterioles of hydronephrotic superoxide dismutase-1 knockout mice. In conclusion, hydronephrosis is associated with changes in the arteriolar reactivity of both hydronephrotic and contralateral kidneys. Increased oxidative stress, reduced NO availability, and stronger reactivity to adenosine of the hydronephrotic kidney may contribute to the enhanced tubuloglomerular feedback responsiveness in hydronephrosis and be involved in the development of hypertension. Key Words: angiotensin II Ⅲ L-NAME Ⅲ oxidative stress Ⅲ NO synthase Ⅲ superoxide dismutase Ⅲ tubuloglomerular feedback H ydronephrosis because of uretero-pelvic junction obstruction is a common condition in newborns, with an incidence of Ϸ1%. Both rats and mice with hydronephrosis, because of chronic partial ureteral obstruction, develop renal injury 1 and salt-sensitive hypertension 2,3 that can be attenuated by relief of the obstruction. 4 The mechanisms are thought to be associated with increased activity of the renin-angiotensin system, 2 increased oxidative stress, and reduced NO availability in the diseased kidney. 5 In micropuncture studies of hydronephrotic animals, the tubuloglomerular feedback (TGF) has a higher responsiveness in the hydronephrotic kidney. 5,6 An increased TGF response, as seen in hydronephrotic kidneys, has also been described in spontaneously hypertensive rats, 7 Milan hypertensive rats 8 during development of hyperte...