Characterization and quantitation of wound matrix in the fetal rabbit.

Fetal response to injury has been characterized by the deposition of a matrix that is not primarily collagen. This study was designed to identify this matrix, in order to better understand the fetal mechanism of tissue repair. Silastic/polyvinyl alcohol sponge (PVA) wound implants were placed paravertebrally in 24-day gestation (31 days = term) fetal (n = 65) and adult (n = 43) rabbits and then harvested from one hour to 6 days post-wounding. Histologic analysis of the fetal wound matrix deposited in the PVA implants suggested the presence of glycosaminoglycans (GAG) rather than the collagen found in adult wound implants. To further analyze the fetal wound matrix, the GAG content was quantitated using an Alcian Blue dye-binding assay. Results showed significantly increased (p less than 0.05) GAG deposition on days 2-6 in the fetal wound compared to the adult wound. Fetal GAG levels were approximately three times those of the adult during this period. Separation of individual GAG species by cellulose acetate electrophoresis demonstrated that the GAG matrix of the fetal wound was composed predominantly of hyaluronic acid. This finding was confirmed by selective enzymatic digestion of separated GAG species using highly specific polysaccharidases. These observations of hyaluronic acid deposition in the fetal wound may be ascribed an important physiologic role by providing a more fluid and malleable matrix rather than a restrictive matrix composed of collagen. This new evidence coupled with earlier findings of the lack of an acute inflammatory response in the fetus further supports the hypothesis that the fetal response to injury is significantly different from the adult response.