[Effect of methodical factors on the in vitro labeling of tissue samples with 3H-thymidine].

The influence of a delayed start of incubation of liver tissue from 7 day old rates on 3H-thymidine incorporation in different cell fractions was studied histoautoradiographically. 10 intervals before incubation (0-360 min) were tested. The TLIs are decreased when incubation is started more than 100 min after tissue excision. In vitro experiments performed immediately after tissue excision show also decreased values in comparison to such incubated 20 min later. The proliferative behaviour of cells which are stored more than 2 hours before incubation is similar to cells of old animals, especially such cells demonstrate a prolongation of their S-phase. Carbogen stimulates 3H-thymidine incorporation but DNA synthesis is not stopped completely when nitrogen is added during incubation.