Tritiated thymidine uptake in pig skin. Comparison of in vivo and in vitro techniques.

Tritiated thymidine (3HT) was used in one of three ways to label deoxyribonucleic acid replication in epidermal cells of miniature swine: (1) the radioactive material was injected intracutaneously in vivo; (2) the radioactive material was injected intracutaneously into biopsy specimens and the specimens incubated in vitro in Eagle's medium, or (3) uninjected biopsy specimens were incubated in Eagle's medium with added 3HT. The first two methods yielded the same proportions of labeled cells with uniform distribution of labeled cells. The third method resulted in labeling of cells mainly at the periphery of the biopsy specimens. The advantages of the in vitro over the in vivo technique of injection of 3HT includes the fact that injecting a biopsy specimen avoids the problems of large amounts of radioactive waste disposal in animal studies or the legal and ethical problems of tracer studies in humans.