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Initiation of DNA Synthesis in Ehrlich Ascites Tumor Cells in Their Plateau Phase of Growth¹

Department of Anatomy, Tulane University, New Orleans, Louisiana 70112

The E₂ hypotetraploid Ehrlich ascites tumor reached its peak size at 1 x 10⁹ cells on the 14th day after i.p. inoculation of 0.30 x 10⁶ cells. During this period the % nonviable Ehrlich ascites tumor cells did not change. Autoradiographic studies during the first 14 days of Ehrlich ascites tumor growth demonstrated no decrease in the % tumor cells incorporating tritiated uridine, proline, phenylalanine, or leucine. The % Ehrlich ascites tumor cells in DNA synthesis (thymidine-³H incorporation), however, decreased with increasing tumor age. Aspiration of most of the tumorous ascitic fluid from a 14-day-old Ehrlich ascites tumor host resulted in recurrent growth of the remaining Ehrlich ascites tumor. Recurrent growth of the Ehrlich ascites tumor was characterized by a significant increase in the thymidine index (% Ehrlich ascites tumor cells incorporating thymdine-³H in 20 min). The peak thymidine index of recurrent growth, 51.8%, occurred between the 14th and 24th (19th) hr after aspiration of most of the 14-day-old tumorous ascitic fluid. During recurrent growth of the Ehrlich ascites tumor a lag period of at least 4 hr occurred between the time of ascites removal and the increase in the thymidine index. Thymidine index determinations made after transplantation of saline-washed 14-day-old Ehrlich ascites tumor cells to new hosts also demonstrated (a) a 4 hr lag period before the thymidine index began to increase and (b) a peak thymidine index, 56.1%, 19 hr after inoculation. The data are discussed in relation to the events in the cell cycle.

¹ Prepared in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Anatomy at Tulane University.

² This work was done while the author was a Public Health Service Predoctoral Trainee. Part of this work was supported by National Science Foundation Grant G 23866 administered by Dr. S. Meryl Rose and a Greater New Orleans American Cancer Society Grant administered by Dr. Ralph N. Baillif.

³ Present address: Department of Anatomy, The University of Arkansas Medical Center, Little Rock, Arkansas 72201.

Received 7/21/67. Accepted 3/ 1/68.