Epidermal ornithine decarboxylase activity and thymidine incorporation following treatment with ultraviolet A combined with topical 8-methoxy-psoralen or anthracene in the hairless mouse

Epidermal thymidine incorporation, as a measure of DNA synthesis, and ornithine decarboxylase activity were estimated in hairless albino mice following phototoxic reactions induced by topical anthracene + UV-A, and topical 8-methoxypsoralen (8-MOP) + UV-A. Both treatments caused depression of epidermal thymidine incorporation to 26% of control values at 4 h; this depression persisted through 24 h following 8-MOP + UV-A. Animals treated with anthracene + UV-A showed a fourfold increase in thymidine incorporation at 48 h, declining at 72 and 96 h; after 8-MOP + UV-A increased thymidine incorporation was observed between 4 and 10 days, when a plateau of 96 h duration was observed. After treatment with anthracene + UV-A, epidermal ornithine decarboxylase activity (ODC) was maximal at 4 h, and exhibited a rapid decline, with normal levels at 48 h. Following 8-MOP, UV-A dose-dependent ODC induction occurred: this was later than that induced by anthracene + UV-A with no detectable activity at 4 or 12 h, and maximum activity at 24 h, the elevation persisting through 96 h. The relationship between ODC induction and epidermal hyperproliferation following these treatments is discussed.