Influence of the timing of switching a protein-free to a protein-containing diet on the wound healing process in a rat all-layer skin defect

We prepared full thickness skin defects in rats fed on a protein-free diet as a hypoproteinaemia model, then switched the animals to a diet containing a normal protein level 1, 6 or 12 days after wounding (inflammatory, granulation and rearrangement phases of the wound healing process) to examine whether improvement in the low-protein state promotes subsequent wound healing. The interval until wound healing in rats fed on a normal protein diet was significantly shorter, whereas that in rats continuously fed on a protein-free diet was significantly longer than those of other groups. Early correction tended to accelerate wound healing. Although wound contraction in groups receiving a protein-corrected or protein-free diet remained similar until 15 days after wounding, thereafter the duration of the rearrangement phase was significantly longer in the protein-free group than in the other groups. The collagen level per unit of granulation tissue area during wound healing was significantly lower in the protein-free group than in the other groups. These findings indicate that protein correction at any time after wounding accelerates wound healing, although early correction is more effective, and reduces the duration of the rearrangement phase more than those of the inflammatory and granulation phases because of the deposit of collagen.