The Measurement of Cell Turnover Rates Using Stable Isotope‐Labelled Thymidine: Experiments On the Small Intestine and On A Transplantable Lymphatic Tumour of the Mouse

Abstract

Multilabelled, non-radioactive thymidine and tritiated thymidine were incorporated simultaneously into the DNA of a rapidly-growing, transplantable mouse lymphoma and the DNA of mouse small intestine by a single intraperitoneal injection of both labelled nucleosides. Mice were killed at selected times during the next 7 days, and the specific activities of the tissues and extracted DNA and the 132/126 mass ratio of thymine isolated from the DNA were determined by scintillation counting and by field ionization mass spectrometry respectively. The rates of decrease of the concentrations of tritiated and stable isotope-labelled thymine in the DNA of the tumour or of the intestine were essentially identical. These results indicate the feasibility of using thymidine multilabelled with stable isotopes for measurement of cell turnover rates in conjunction with cancer therapy.