Epidermal DNA synthesis: a new disc technique for evaluating incorporation of tritiated thymidine

We present a new technique for evaluating epidermal DNA synthesis as measured by incorporation of tritiated thymidine. Standard areas of epidermis were isolated by glueing plastic discs to the skin followed by heating on a hot plate at 60 degrees C. The discs were then cut out and the dermis gently separated and removed by incubation at 60 degrees C in 2 M potassium bromide. The discs with attached epidermis were washed in 0.25% acetic acid to remove unincorporated tritiated thymidine and then counted in a liquid scintillation counter. Results were expressed as disintegrations per minute per disc. This technique showed good correlation to the hydroxylapatite column and perchloric acid methods for extracting DNA, but was considerably less tedious and subject to fewer errors. Incubation of discs in DNAse indicated radioactivity was primarily in DNA. The disc technique is simple, rapid and inexpensive and could be performed in large numbers even in unsophisticated laboratories.