ARGININE-FREE DIET SUPPRESSES NITRIC-OXIDE PRODUCTION IN WOUNDS

To determine the effects of dietary arginine on nitric oxide production during would healing, we fed male Sprague-Dawley rats a low nitrate diet containing 0% or 3% L-arginine. Nitrate from daily urine samples was reduced to nitric oxide and measured with a chemiluminescence analyzer to indirectly assess nitric oxide synthesis. Once baseline nitrate levels were established, rats received circular, full thickness dermal wounds. The results demonstrate that dietary arginine is not necessary for the sudden increase in nitrate output immediately after wounding, although removal of arginine appears to limit the maximum amount of nitric oxide produced. Arginine-deficient rats had significantly lower (P < 0.001) urinary nitrate levels than the corresponding 3%-arginine group over the entire experiment. Despite lower nitrate output in the arginine-free animals, the early response to wounding was similar in both the arginine-free and 3%-arginine groups, as nitrate output doubled within 48 hours of wounding (+112% and +104%, respectively). However, endogenous arginine was not sufficient to maintain increased nitrate output, which returned to baseline levels in arginine-free animals within 11 days after wounding, while the nitrate output of the 3%-arginine group remained significantly elevated (+30-60%, P < 0.001) through day 30 and wound closure. In addition, animals on the arginine-free diet increased nitrate output 14-fold in response to lipopolysaccharide challenge. These results suggest that removing dietary arginine does not prevent the cytotoxic activity of macrophages during the inflammatory response, but suppresses nitric oxide synthesis during later tissue repair. This may help explain previous evidence that supplemental arginine improves wound heating, although video image analysis of wounds was inconclusive.