Fetal response to injury in the rabbit

Fetal, neonatal, and adult tissue response to a standardized injury was studied using subcutaneous wound implants, linear incisions, and punch wounds in New Zealand white rabbits. In the fetus, sutured incisions healed by primary intention without antecedent inflammation. However, neither contraction nor healing by secondary intention was seen in punch or unsutured wounds. Healing both by primary and secondary intention following inflammatory infiltration was observed uniformly in neonatal and adult rabbits. Wound implants were extensively infiltrated with collagen in the adults studied; however, no collagen was seen in fetal implants and collagen hydroxyproline content could not even be detected by high performance liquid chromatography techniques; rather, a matrix rich in hyaluronic acid was found. The fetal tissue response to injury differs from the adult, proceeding in the absence of a classical inflammatory stimulus and lacking contractile capabilities. The deposition of extracellular matrix rich in hyaluronic acid but devoid of collagen suggests that the fetal response to injury may be a process more closely resembling regeneration or growth rather than repair by scar deposition.