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The Cell Cycles of Three Transplantable Morris Hepatomas¹

Fels Research Institute and Department of Pathology, [T.S., R.B.], Temple University School of Medicine, Philadelphia, Pennsylvania 19140, and Department of Biochemistry, Howard University, Washington, D. C. 20001 [H. P. M.]

The length of the cell cycle and its phases and the growth fraction were studied in vivo in 3 transplantable rat hepatomas: a fast growing one (5123 tc), one of intermediate growth rate (7794A), and a slowly growing one (7793). The length of the cell cycle and the growth fraction for each of these tumors were found to be: 27 hr and 0.8 for 5123 tc, 49 hr and 0.42 for 7794A, and 234 hr and 0.4 for 7793. However, the values for 7793 are open to a considerable degree of uncertainty. The cell cycle times of each transplantable hepatoma were substantially similar whether a tumor was grown in the right or left thigh. Each tumor showed marked variations in the cell cycle of individual tumor cells, especially in the G₂ period. For instance, the length of G₂ in hepatoma 7793 varied from 5 to 40 hr.

¹ Supported by USPHS Research Grants CA-08373, CA-10729, and CA-07174 from the National Cancer Institute.

Received 6/19/69. Accepted 8/19/69.