Open wounds in the fetal rabbit do not heal by contraction and actually expand between 60% and 90% over a period of 5 days. Experiments were carried out to determine whether transforming growth factor-β1 can reduce expansion of open wounds in the fetal rabbit. This study was based on the concept that transforming growth factor-β1 causes differentiation of fibroblasts into contractile fibroblasts or "myofibroblasts." To test this hypothesis, pregnant New Zealand White rabbits underwent laparotomy and hysterotomy on day 24 of gestation. A circular full-thickness cutaneous wound was made on the back of each fetus. After wounding, either vehicle alone or vehicle with transforming growth factor-β1 was applied topically to the wound site, and each fetus was then returned to the uterus. The hysterotomy and laparotomy were closed in standard fashion. On postoperative day 5, fetuses were harvested by repeat Cesarean section. Wound areas were determined from photographs, calculated as percentage of original wound size, and expressed in square millimeters. In addition, a portion of each wound was fixed and processed for histologic and immunohistochemical analysis. At harvest, the control wounds had expanded by an average of 87% of the original area. In marked contrast the transforming growth factor-β1-treated wounds had only expanded an average of 16%. Thus, transforming growth factor-β1 significantly decreased the area of the open fetal wounds compared with control (p < 0.001). By histologic examination, no significant difference was found between the test group and the control group with regards to inflammation, neovascularization collagen deposition, elastin content, glycosaminoglycan content, or hyaluronic acid content. Most notably, however, there was an increased density of fibroblasts in the transforming growth factor-β1-treated group. In addition, immunohistochemical staining with an anti-α-smooth muscle actin antibody showed the presence of contractile fibroblasts in the wound margins in the transforming growth factor-β1-treated group but failed to show any positive-staining fibroblasts in the matrices of the control group. These results indicate that open wounds in the fetal rabbit treated in vivo with transforming growth factor-β1 were significantly smaller than control wounds. This process appears to result from the recruitment and differentiation of normal dermal fibroblasts into contractile fibroblasts containing α-smooth muscle actin.
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