Topical application of retinole acid to mouse skin led to a dramatic inhibition of phorbol ester (12-O-tetradecanoylphorbol-13-acetate)-induced epidermal ornithine decarboxylase (EC 4.1.1.17) activity, an event proposed to be essen tial for tumor promotion. The degree of inhibition was de pendent on the dose and time of application of retinoic acid. In contrast, treatment with retinoic acid did...
