INTRODUCTION: This study evaluated the effects of a combination of 1400W ((3(aminomethyl)benzyl)acetamidine), a highly selective iNOS (inducible NO synthase) inhibitor, and SNAC (S-nitroso-N-acetylcysteine), an NO donor, on microcirculation in reperfused skeletal muscle. METHODS: The left cremaster muscle of 87 rats weighing 90-110g underwent 5h of ischemia followed by 90min of reperfusion. The rats were divided into innervated (n=43) and denervated (n=44) groups. Each group was further divided into 3 subgroups treated with intravenous PBS, subcutaneous injection of 1400W (3mg/kg), or a combination of subcutaneous 1400W (3mg/kg) and intravenous SNAC (100nmol/100gm/min). The agents were administered 30 min before reperfusion and SNAC infusion was continued throughout the reperfusion. At 10 minute intervals during reperfusion, vessel diameters were measured by intravital microscopy and blood flow was measured by laser doppler. RESULTS: 1) In the innervated model, treatment with both agents yielded a maximal flow of 137±27% of baseline at 40 minutes, compared to 127±22% at 80 minutes with 1400W and 102±23% at 90 minutes in controls. Time to return of baseline flow improved from 67.5±17.5 minutes in controls to 40.0±15.1 minutes for 1400W (p<.01 compared to control) and 20.0±9.2 minutes for both agents (p<.01 compared to 1400W). Treatment with both agents led to greater vessel diameters than 1400W alone or control at nearly all time points. The greatest difference occurred at 20 minutes in 10-20 micron vessels (65± 12% of baseline diameter for controls, 77±11% for 1400W, and 99± 21% for both agents) (p<.05 for both agents compared to 1400W). 2) In the denervated model, flow returned to baseline in 8 out of 8 rats in an average of 35.6±13.3 minutes for both agents, whereas only 2 out of 8 1400W-treated rats and 1 out of 8 control rats returned to baseline flow. Vessel diameters were greater at nearly all time points in rats treated with both agents than 1400W or control groups. DISCUSSION: This study demonstrated that a combination treatment of 1400W and SNAC restored microcirculation better than 1400W alone in both innervated and denervated reperfused muscle. The fact that a combination treatment of NO donor and iNOS inhibitor resulted in greater maximal flow and earlier restoration of baseline flow than iNOS inhibitor alone suggests that supplementation of NO to I/R tissue is important for improvement of microcirculation and reduction of I/R injury. The ability of NO donor SNAC to reduce I/R injury appears to protect small arterioles from vasospasm.