The proliferation response of rat liver parenchymal cells after partial hepatectomy. A methodological study comparing flow cytometry of nuclear DNA content and in vivo and in vitro uptake of thymidine.

DNA synthesis in rat hepatocytes, from livers regenerating after 70% hepatectomy, was assessed by flow cytometric determination of nuclear DNA content and by incorporation of [3H]thymidine. Parenchymal liver cells were isolated by collagenase perfusion and low-speed centrifugation. Nuclei from the isolated cells were prepared for flow cytometry by a treatment with detergent, pepsin and RNase, and stained with ethidium bromide. Parallel samples of cells were incubated with [3H]thymidine and analysed for rate of incorporation of radioactivity into DNA and for labelling index determination. The flow cytometric measure of the replicative response, i.e. the presence of cells with S-phase DNA content within the diploid and tetraploid cell populations, was compared with the incorporation of [3H]thymidine. For each of fourteen animals, including two control rats and twelve partially hepatectomized animals killed either before (at 13 hr after hepatectomy), at the onset (16 and 18 hr) or at the peak (24 hr) of regenerating activity, a fairly good correlation was found between the different methods. Satisfactory resolution of the flow cytometric detection of S-phase cells was indicated by a sorting experiment using an Ortho (system 50-H) cell sorter which demonstrated that after [3H]thymidine injection in vivo 88% of the diploid and 84% of the tetraploid S-phase nuclei were labelled, while labelling in the G1-fractions was only 2 and 7%, respectively.