Hsp72 induction: A potential molecular mediator of the delay phenomenon

The molecular basis of enhanced ischemic tissue survival in flaps precondit ioned by surgical delay is poorly understood, Because elevated expression o f so-called heat shock or stress proteins has been shown to protect tissues /organs against ischemic injury, the authors examined whether the levels of the most highly induced stress protein-hsp72-were elevated in delayed musc le flaps using a rat muscle flap model. Bilateral latissimus dorsi muscle f laps based on the thoracodorsal vessels were elevated in 16 male Sprague-Da wley rats, For each animal, one side was selected randomly to undergo preco nditioning by surgical delay for a 7-day period prior to elevation, Delay w as accomplished by preserving the thoracodorsal pedicle and a single large distal intercostal perforating vessel. After bilateral flap elevation, lati ssimus dorsi tissue was harvested from proximal, central, and distal flap s egments 0, 1, 3, and 7 days postoperatively (N = 4 for each group), and was analyzed for the expression of hsp72 via Western blot analysis. At the tim e of harvest, flap viability was assessed by staining with nitroblue tetraz olium. Flap perfusion was measured prior to muscle elevation and harvest us ing laser Doppler flowmetry. The results demonstrate that delayed muscle fl aps had significantly greater total perfusion (p < 0.05) and survival (p < 0.03) 1, 3, and 7 days after elevation compared with the acutely elevated c ontrol tissue. Western blot analysis revealed that tissues harvested from t he delayed flaps expressed substantially higher levels of hsp72 compared wi th the acutely elevated control samples, Segmental analysis also revealed a proximal > middle > distal expression of hsp72 in the delayed flaps (p < 0 .05). Flap preconditioning by surgical delay increases the expression of hs p72. Moreover, regional differences in hsp72 gene expression are associated with differences in perfusion and survival of delayed muscle flaps. These results indicate that hsp72 may play a substantial role in mediating the de lay phenomenon.