Determination of growth kinetics in a renal sarcoma of the rat by double labeling with 14C- and 3H-thymidine.

An in vitro double-labeling technique for determination of kinetic growth parameters was tested; 13 renal sarcomas of rats were incubated after excision under standardized conditions with 14C- and 3H-thymidine successively. Another ten tumors were evaluated after in vivo double injection of 14C and 3H-thymidine into sarcoma-bearing animals. In both groups histoautoradiography was performed using a simple stripping-film method. Results including labeling indices, mitotic indices, length of DNA-synthesis phase and cell-production rate obtained by both methods were in excellent agreement. All values fitted those determined in earlier experiments using a continuous labeling and a fraction-labeled-mitoses method in vivo. Theoretical considerations on the calculation of kinetic parameters by double labeling have been added. The experimental results found in this study represent a base for evaluation of biopsies from human tumors.