Novel method to investigate kinetics of rat skin cells by means of an occlusive dressing method using...

We developed a novel technique to detect S-phase skin cells by applying bromodeoxyuridine (BrdU) epicutaneously using an occlusive dressing (OD) method. BrdU was scarcely absorbed from the skin with a simple epicutaneous application, whereas the incorporation of BrdU was very well promoted with the use of our OD method. We applied BrdU on the backs of rats using this method and investigated the conditions required for an optimal response, with a special focus on the period of application, the concentration of BrdU used and vehicles suitable for the immunocytochemical staining of this agent. From these experiments, we were able to determine that an application time of at least 60 min was necessary to liable S-phase cells, a 2% concentration of BrdU was needed to obtain consistent labeling and aqueous vehicles are satisfactory solvents for BrdU preparations. Epidermal keratinocytes and S-phase cells in the upper portion of dermis were clearly labeled after either intraperitoneal injection of BrdU or after administration by means of the OD method. To ascertain whether this latter method could provide an effective alternative to intraperitoneal injection, we compared the labeling patterns of both methods with respect to the speed of migration of BrdU-labeled basal cells from the basal layer to the horny layer of epidermis. Using either of these two methods, basal keratinocytes were labeled immediately after administration. Three days after the first administration, BrdU-labeled cells were detected in the middle layer of the epidermis, but after 8 days, they were no longer evident in epidermal tissue. As another means of comparing both methods, we used antibody to proliferating cell nuclear antigen (PCNA) and compared the ratio of PCNA-positive basal cells to BrdU-labeled basal cells. The number of PCNA-positive cells was about 4.6 times greater than the number of BrdU-labeled basal cells by both methods. We concluded that the OD method could be used as a substitute for intraperitoneal injection in order to observe cell kinetics using bromodeoxyuridine.