Effect of epidermal growth factor on cell proliferation in normal and wounded connective tissue

Epidermal growth factor has been previously shown to stimulate connective tissue repair in the perforated rat mesentery. The mechanism by which epidermal growth factor accelerates closure of mesenteric perforations has not been established, but epidermal growth factor may stimulate mitosis, contraction, migration, or angiogenesis. In the present investigation, the effect of epidermal growth factor on connective tissue cell proliferation was studied during the initial phase of repair of mesenteric perforations and in unwounded mesentery. Laparotomies were performed on Sprague-Dawley rats, and standardized perforations were made with a scalpel in the center of the mesenteric "windows," leaving every second window as an internal control. Twice daily for 4 consecutive days, beginning on the day of surgery, the animals received by intraperitoneal injection either 10 microg of epidermal growth factor dissolved in phosphate-buffered saline solution or phosphate-buffered saline solution alone. Cell proliferation was measured by either mitotic index of fibroblasts and mesothelial cells or DNA content of individual fibroblast cell nuclei in the wound area or in unperforated control windows. Laparotomy alone was found to enhance proliferation during the early postoperative period, as shown by increased numbers of S + G2 fibroblasts and a greater mitotic index. Epidermal growth factor treatment increased the mitotic index in perforated windows on the third postoperative day, compared with controls treated with phosphate-buffered saline solution, but did not significantly increase either the number of S + G2 fibroblasts or the mitotic index in unwounded tissue. Also, the proliferative response after epidermal growth factor treatment was significantly higher in wounded tissue. This study shows that epidermal growth factor stimulates proliferation of connective tissue cells in wounded but not unwounded tissue, and such enhancement of fibroblast proliferation might be of importance in epidermal growth factor-stimulated connective tissue repair.