ABSTRACT
BACKGROUND: Constitutive nitric oxide synthase (cNOS) may produce species involved in ischemia/reperfusion (I/R) injury: NO in the presence of sufficient L-arginine and superoxide at the diminished local L-arginine concentration accompanying I/R. METHODS AND RESULTS: During hindlimb I/R (2.5 hours/2 hours), in vivo NO was continuously monitored (porphyrinic sensor), and L-arginine (chromatography), superoxide (chemiluminescence), and I/R injury were measured intermittently. Normal rabbits were compared with those infused with L-arginine 4 mg x kg(-1) x min(-1) for 1 hour. In both groups, approximately 6 minutes into ischemia, a rapid increase of NO from its basal level of 50+/-17 to 115+/-7 nmol/L, P<.005 (microvessels), was observed. In animals not treated with L-arginine, NO dropped below basal to undetectable levels (<1 nmol/L) during reperfusion. In animals treated with L-arginine, the decrease of NO was slower, such that substantial amounts accumulated during reperfusion (25 nmol/L). Decreased NO during I/R was accompanied by increased superoxide, which during reperfusion reached 50 nmol/L without or 23 nmol/L with L-arginine treatment. Calcium-dependent cNOS was a major source of superoxide release (inhibited 70% by L-NMMA and 25% by L-NAME) during I/R. CONCLUSIONS: L-Arginine treatment decreased superoxide generation by cNOS while increasing NO accumulation, leading to protection from constriction (microvessel area, 17.77+/-0.95 versus 11.66+/-2.21 microm2 untreated, P<.0005) and reduction of edema after reperfusion (interfiber area, 16.56+/-2.13% versus 27.68+/-7.70% untreated, P<.005).