Histologic alterations in dermal repair after thermal injury effects of topical angiotensin II

Previously, we determined that quantitative assessment of epithelialization of the burn site could be performed using quantitative immunohistochemistry with an antibody to the protein cyclin. In this study, the effect of administration of angiotensin II (AII) on two histologic parameters of healing - the number of vascular channels at the burn site and the number of cells proliferating in hair follicles at the edge of the burn and within the burn - were evaluated. Beginning on day 4, vascular channels were noted within the burn site. Significantly more channels were noted in the burns treated with AII than those treated with placebo. With the exception of 3 postinjury days, this increase continued through day 17. Thereafter, the number of vascular channels peaked, and no differences were noted between control and treated burns. The number of cells proliferating in the hair follicle was also evaluated. At the edge of the burn, on average, 126 cells per microscope field (10x) were undergoing proliferation in the AII-treated burn on days 1 through 16 after burn injury. This is approximately a 50% increase over the number of calls proliferating in the placebo-treated burns. On day 12 (approximately 5 days before that observed in control burns), this AII-dependent proliferative response began to increase and peaked on day 19 at a level comparable to control. Thereafter, the proliferative response remained at this level through day 28. Within the area of the burn on days 1 through 15, 21 cells per medium power field on average (approximately 50% more than control) were undergoing proliferation. As on the edge of the burn, an AII-dependent increase in the number of cells proliferating in the hair follicles was observed during the latter phase of healing (on day 16 after the initiation of injury). However, unlike the edge of the burn, administration of AII led to a continued increase (approximately 50%) in the number of cells per field undergoing proliferation. AII increased neovascularization and cellular proliferation after burn injury. Through an increase in these two cellular events, AII may in turn accelerate healing of tissues after thermal injury.