Ornithine decarboxylase in rat skin: 2. Differential response to hair plucking and a tumor promoter.

Ornithine decarboxylase (OCD; EC 4.1.1.17) activity is induced in dorsal rat skin by either application of the tumor promoter 12-0-tetradecanoyl-phorbol-13-acetate (TPA) or by hair plucking. In TPA-treated rat skin, ODC activity does not rise above controls until 3 hr posttreatment. Following a peak at 4 hr, ODC activity declines until it reaches control levels at 12 hr. In contrast, stimulation of skin by hair plucking causes a 50% decrease in ODC activity by 1 hr. Enzyme activity then increases linearly to a peak at 4 hr and remains at 3 times control levels up to 12 hr. In skin stimulated by both hair plucking and TPA, and peak activity is found to exceed the maximum of either stimulus alone in an additive manner. The response to TPA occurs mainly in the epidermis, while both the epidermis and dermis show a substantial response to hair plucking. Both stimuli cause a lengthening of the half-life of ODC. Stimulation of ODC by hair plucking is insensitive to indomethacin administration but the TPA-response is inhibited 74%. Stimulation of ODC by hair plucking is inhibited by Actinomycin D only if Actinomycin D is given at the time of stimulus administration, and then only partially. The TPA-response is fully inhibited by Actinomycin D if given at the time of TPA application. Inhibition is roughly proportional to the duration of Actinomycin D treatment up to the activity peak at 4 hr. These results indicate that the tumor promoter, TPA, and the more physiological stimulus, hair plucking, stimulate skin ornithine decarboxylase activity by different mechanisms.