Regulation of inducible nitric oxide synthase in ischemic preconditioning of muscle flap in a rat model.

Purpose: Ischemic preconditioning has been shown to influence flap tolerance to prolonged ischemia. Nitric oxide (NO) synthesis is one of the proposed mechanisms involved in ischemic preconditioning. In this study, the molecular marker of NO is examined in correlation with ischemic preconditioning on improving muscle flap survival.

Methods: Fifty male Sprague-Dawley rats were randomized into experimental and control groups. The gracilis muscle flap with femoral vascular pedicle was used as a flap model. Ischemic preconditioning consisted of 3 sequences of clamping the pedicle for 10 minutes followed by 10 minutes of reperfusion for a total of 1 hour. In part I, the experimental group (n = 10) underwent ischemic preconditioning for 1 hour. In the control group (n = 10), the flaps were dissected without clamping of the pedicle. Both groups were then subjected to 4 hours of global ischemia by continuous pedicle clamping, after which the flaps were sutured to their beds. On postoperative day 3, flap survival was determined by gross and histologic examinations. The evaluators were blinded to the treatment. In part II, the experimental group (n = 12) underwent ischemic preconditioning, while the control group (n = 12) did not. The flaps from each group were harvested for inducible nitric oxide synthase (iNOS) gene expression using reverse transcriptase-polymerase chain reaction at the end of 1 hour after reperfusion and at 4 hours of global ischemia.

Results: The results indicated a significantly higher survival rate in the experimental group than in the control group (90 versus 50%, P < 0.05). iNOS gene expression was significantly higher in the experimental group than in the control group at 1 hour after ischemic preconditioning (0.73+/-0.18 versus 0.26+/-0.11, P < 0.01). However, after 4 hours of global ischemia, iNOS expression in the control group was statistically higher than in the experimental group (0.83+/-0.16 versus 0.26+/-0.07, P < 0.01).

Conclusions: We conclude that ischemic preconditioning can enhance flap tolerance to ischemia-reperfusion injury and improve flap viability rate. This study provides evidence that the regulation of NOS may play a role in ischemic preconditioning phenomenon and warrants further investigation.