Changes in polyamine metabolism in WI38 cells stimulated to proliferate.

Quiescent confluent monolayers of WI38 human diploid fibroblasts were stimulated to proliferate by replacement of the exhausted medium with fresh medium containing 10% fetal calf serum. The cellular content of the polyamines, putrescine, spermidine, and spermine was studied at various intervals after the nutritional change. The putrescine content increased during the pre-replicative phase of the cell cycle, whereas the content of spermidine and spermine did not increase until after the initiation of DNA synthesis. By varying the composition of the stimulating medium it was possible to alter the percentage of cells that were stimulated to proliferate. Measurement of the cellular polyamine content and ³H-thymidine (³H-TdR) incorporation into DNA at the time of the maximal rate of DNA synthesis showed that the magnitude of putrescine accumulation depended on the percentage of cells that were stimulated to proliferate. These results indicate that there may be a connection between polyamine synthesis and subsequent DNA replication.