The Effect of Croton Oil Pretreatment on Skin Tumor Initiation in Mice 1

A single application of 0.5% croton oil to mouse skin stimulates nucleic acid and protein synthesis in the treated area. The maximum rates of synthesis were attained at 6 hours for RNA, 12 hours for protein, and 18 hours for DNA. By 48-72 hours, the rate of synthesis of RNA and protein was returning to normal, but the rate of DNA synthesis was still 2-3 times the control value. In order to test the hypothesis that cells synthesizing DNA are more susceptible to initiation of skin tumor formation, mice were given a single, preliminary application of croton oil either 18 or 48 hours before initiation with 7,12-dimethylbenz [a] anthracene (DMBA), /3-propiolactone (BPL), or urethan. Tumors were subsequently elicited by multiple applications of croton oil. Croton oil pretreatment did not affect initiation by BPL, caused a slight increase in tumor yield after initiation by DMBA, but clearly increased tumor incidence in mice initiated with urethan. The overall binding of DMBA-3H to mouse skin DNA, RNA, and protein, or to RNA fractionated on a methylated albumin kieselguhr column, was not greatly affected by the croton oil pretreatment.