Acute effect of DMBA application on mitotic activity of hamster buccal pouch epithelium

One, two, or three applications of a 0.5% solution of DMBA in mineral oil were made to the buccal pouches of three groups of hamsters. There were 10 animals in each group, and additional groups of 10 animals were used as mineral oil controls. Mitotic activity was studied in epithelial whole mounts of buccal pouch following intraperitoneal injection of vinblastine (VBL) in a dose of 4 mg per kilogram of body weight 4 1/2 hours, 24 hours, 48 hours, 1 week, and 2 weeks after treatment. Similar groups of animals were used for a thymidine-labeling experiment. Immediately after the last DMBA application to buccal pouches, 3H-TdR was injected intraperitoneally in a dose of 1 microcurie per gram of body weight. All labeling was studied autoradiographically in epithelial whole mounts of buccal pouches stained with hematoxylin. A cell with five or more grains of label per nucleus was considered labeled. It was found that with one application of DMBA mitotic activity, as studied after VBL injection, was greatly reduced during the experimental period of 2 weeks. After two DMBA applications there was a significant reduction in mitotic activity in the first 48 hours but a return to normal by 2 weeks, indicating a reaction to the damage produced by the two DMBA applications. The thymidine-labeling study tended to confirm this result. The label in the animals that received two DMBA applications disappeared after 48 hours, indicating increased mitotic activity and tissue repair, while animals with one DMBA application maintained the label after 1 week.