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The unknown biochemical role of arginase in epidermal metabolism was probed by examining the association of elevated arginase activity with epidermal hyperplasia and hyperkeratinization. Epidermal hyperplasia was induced experimentally by topical application of 1-decanol to the right side of male hairless mice while the contralateral side served as control. Arginase activity, incorporation of 3H-thymidine into DNA, DNA and protein content were measured in the separated control and experimental epidermis six hours and on days 1 through 5 and 7 after 1-decanol application. After six hours, the epidermis appears damaged histologically, and DNA synthesis is inhibited. By day 1, incorporation of 3H-thymidine into DNA is elevated and a new hyperplastic epidermis has formed beneath the original epidermis. Epidermal arginase is elevated two through seven days after 1-decanol application and always is associated with continuing epidermal hyperplasia. The stimulation of DNA synthesis, which parallels the induction of epidermal hyperplasia by 1-decanol, precedes the induction of epidermal arginase activity. An attempt to relate these results with polyamine synthesis and other metabolic events is made.

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