The effect of systemic treatment with 5-fluorouracil on the epidermis of the guinea pig.

The thymidine labelling index and the mitosis rate (blocked by colcemid) in the basal cell layer of the guinea pig were determined before and during treatment with 5-fluorouracil (1 mg i.p. in 2 day's interval/100 g body weight). Additionally, the epidermal area and thickness and the number and size of cells were measured. 5-Fluorouracil equally reduces the thymidine labelling index and the mitosis rate with the full effect after treatment of at least 22 days. From these findings it is concluded that the S-phase--calculated from the end of the thymidine synthesis--is not altered. Furthermore atrophy of the epidermis runs parallel with the reduction of the 3H thymidine labelling index and the mitosis rate.