Radiation-induced reoxygenation in the SCCVII murine tumour: evidence for a decrease in oxygen consumption and an increase in tumour perfusion.

Radiation-induced reoxygenation of the SCCVII murine tumour was examined with the goal of determining whether rapid reoxygenation in this tumour occurs as a result of cell loss, redistribution of hypoxic cells within the tumour cord, a change in oxygen consumption rate, or a change in tumour perfusion. Six hours after exposure of the tumour to 10 Gy, oxygen diffusion distance, measured using tumour cubes incubated with a fluorescent hypoxia probe, had increased by about 20%, corresponding to a reduction of about 16% in oxygen consumption rate. Cell loss and redistribution within the tumour cord were negligible at this time. Hypoxic fraction, measured using the comet assay, indicated a significant decrease from 18% hypoxic cells in unirradiated tumours to 6% in tumours examined 6 h after 10 Gy. Changes in tumour perfusion were also measured using the dual fluorescent dye method which allows detection of regions undergoing transient fluctuations in perfusion. Six hours after 10 Gy, the percentage of blood vessels labeled with only one stain had decreased from 8.6% to 4.5%. Results indicate that the rapid reoxygenation of the SCCVII tumour following exposure to 10 Gy can be attributed, not to cell loss or redistribution, but to a decrease in oxygen consumption and an increase in tumour perfusion.