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Abstract:
A standardized in vitro system for the measurement of 3H-thymidine incorporation into tissue explants is described, and by its use a good correlation is demonstrated between relative tritium activity per mg wet wt and autoradiographic thymidine labelling index (L.I.). The value of this technique as a method of determining overall L.I.s is discussed, especially as regards tissues with a low L.I. or with a highly inhomogeneous distribution of DNA synthesizing nuclei, as often occurs in tumours.
The importance of the oxygen partial pressure in the incubated explants for the process of DNA synthesis and hence for the demonstration of 3H-labelled nuclei is considered both theoretically and on the basis of experimental data. Results of measurements on the kinetics of 3H-thymidine incorporation in the in vitro system are presented.
