Uncoupled NOS is a major source of renal superoxide in angiotensin II‐induced hypertension

Superoxide (O 2 •− ) in the kidney has been implicated in the genesis of high blood pressure. We sought to determine the source of renal O 2 •− in hypertension. We found that angiotensin II infusion for 2 weeks increases renal medullary O 2 •− production (from 29 ± 3 to 48 ± 3 pmol/mg, p<0.005) and to a lesser extent in the cortex (from 35 ± 4 to 52 ± 7 pmol/mg) as measured by dihydroethidium oxidation and HPLC. Surprisingly, we found that NADPH oxidase activity was not augmented by angiotensin‐II. In contrast, the NO synthase (NOS) antagonist L‐NAME abolished the increase in O 2 •− in both cortex and medulla, indicating uncoupled NOS as the source of renal O 2 •− in hypertension. In studies to determine why angiotensin II causes NOS uncoupling we found that angiotensin II‐infusion dramatically decreased total pterins in both the medulla (11.8 ± 6 to 3.2 ± 0.5 pmol/mg, p<0.05) and cortex (10.5 ± 3.4 to 3.6 ± 0.1 pmol/mg, p<0.05). Further studies showed that the rate limiting enzyme for BH 4 production, GTP cyclohydrolase‐1 (GTPCH‐1), was unchanged by western blot but that its activity is paradoxically increased 10‐fold by angiotensin II (p<0.005). Urine measurements showed that angiotensin‐II induces renal loss of pterins. We conclude that hypertension is associated with a profound depletion of renal pterins, leading to NOS uncoupling, at least in part by increased urinary excretion. Research support: American Heart Association (fellow grant southeast affiliate).