USE OF A NITRIC-OXIDE PRECURSOR TO PROTECT PIG MYOCUTANEOUS FLAPS FROM ISCHEMIA-REPERFUSION INJURY

Nitric oxide is a radical with vasodilating properties that protects t issues from neutrophil-mediated ischemia-reperfusion injury in the hea rt and intestine. Previous studies in our laboratory suggested that L- arginine, a nitric oxide precursor, can protect skin flaps from ischem ia-reperfusion injury. In this study, we examined the effects of L-arg inine on the survival of myocutaneous flaps in a lar-ge animal model a nd established whether this effect was mediated by nitric oxide and ne utrophils. Two superiorly based 15 x 7.5 cm epigastric myocutaneous is land flaps were dissected in 15 Yorkshire pigs weighing 45 to 50 kg. O ne of the flaps was subjected to 6 hours of arterial ischemia and then reperfused for 4 hours (ischemia-reperfusion flaps), whereas the othe r flap was used as a non-ischemic control (non-ischemia-reperfusion fl aps). The flaps were divided into four groups: control non-ischemia-re perfusion flaps that received only saline (group I); ischemia-reperfus ion flaps that were treated with saline (group II); and flaps treated with either L-arginine (group III) or N<(omega)over bar>-nitro-L-argin ine methylester (L-NAME), a nitric oxide synthase competitive inhibito r, plus L-arginine in equimolar amounts (group IV). These drugs were a dministered as an intravenous bolus 10 minutes before the onset of rep erfusion, followed by a 1-hour continuous intravenous infusion. Full-t hickness muscle biopsies were taken at baseline, 3 and 6 hours of isch emia, and 1 and 4 hours of reperfusion. The biopsies were evaluated by counting neutrophils and measuring myeloperoxidase activity. At the e nd of the experiment, skeletal muscle necrosis was quantified using th e nitroblue tetrazolium staining technique, anti a full-thickness biop sy of each flap was used for determination of water content. Statistic al analysis was performed using analysis of variance and the Newman-Ke uls test. Non-ischemia-reperfusion flaps showed no muscle necrosis. Is chemia-reperfusion flaps treated with saline had 68.7 +/- 9.1 percent necrosis, which was reduced to 21.9 +/- 13.6 percent with L-arginine ( p < 0.05). L-NAME administered concomitantly with L-arginine demonstra ted a necrosis rate similar to that of saline-treated ischemia-reperfu sion flaps (61.0 +/- 17.6 percent). Neutrophil counts and myeloperoxid ase activity after 4 hours of reperfusion were significantly higher in ischemia-reperfusion flaps treated with L-NAME and L-arginine as comp ared with the other three groups (p < 0.05). Flap water content increa sed significantly in ischemia-reperfusion flaps treated with saline an d L-NAME plus L-arginine versus non-ischemia-reperfusion flaps (p < 0. 02) and L-arginine-treated ischemia-reperfusion flaps (p < 0.05), Ther e was no difference in flap water content between ischemia-reperfusion flaps treated with L-arginine and non-ischemia-reperfusion flaps. Adm inistration of L-arginine before and during the initial hour of reperf usion significantly reduced the extent of flap necrosis, neutrophil ac cumulation, and edema due to ischemia-reperfusion injury in a large an imal model. This protective effect is completely negated by the use of the nitric oxide synthase blocker L-NAME. The mechanism of action see ms to be related to nitric oxide-mediated suppression of ischemia-repe rfusion injury through neutrophil activity inhibition.