A transition zone between well‐perfused proximal tissue and inadequately perfused distal tissue was evaluated histologically and biochemically in skin flaps. Cranially based pedicle flaps, 3 × 7.5 cm, were made on the backs of female Sprague‐Dawley rats. Flap survival was 22% of the original flap area at 7 days and 40% at 14 days after flap elevation (p < 0.001). The transition zone consisted of full‐thickness skin survival proximally and partial‐thickness wound distally. It is evident that skin wounds induced by ischemia or reperfusion repair continuously between 7 and 14 days after flap elevation. Tissue glucose, lactate, and hypoxanthine levels were measured to assess capillary perfusion in the transition zone on postoperative day 3. The proximal full‐thickness skin 5 mm from the wound margin demonstrated no significant changes in glucose and lactate levels compared with normal skin. The partial‐thickness wounds exhibited no change in glucose (a 33% decrease was not statistically significant) but a significant increase (319% of normal) in lactate level (p < 0.05). Hypoxanthine levels increased to 453% of normal in full‐thickness skin (p < 0.01) and to 787% in partial‐thickness wounds (p < 0.001). Metabolic response was evaluated by enzyme assays in the transition zone. Hexokinase activity increased by 251% of normal (p < 0.05), glucose 6‐phosphate dehydrogenase by 245% (p < 0.01), and glutathione reductase by 184% (p < 0.05) in the proximal full‐thickness skin. Hexokinase activity further increased by 482% of normal (p < 0.01), glucose 6‐phosphate dehydrogenase by 379% (p < 0.05), and glutathione reductase by 346% (p < 0.01) in partial‐thickness wounds. The results suggest that partial‐thickness wounds have less capillary circulation but greater antioxidant enzyme activities than does the survival area with full‐thickness skin.
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