The radioresponsiveness of normal and tumour microvasculature

Mouse tails bearing DMH-II tumours were irradiated to a total of 80 Gy in 8 Gy fractions, twice a day for 5 consecutive days. The normal tail vasculature was minimally affected for up to 60 days post-irradiation. In contrast tumour capillaries which showed minor changes on day 6 post-irradiation were severely affected by day 14. DMH-II proved to be a radioresistant tumour. The radiation dose used in this experiment was the maximum total dose which could be tolerated by the mouse tail. The tumour began to regenerate at approximately 40 days post-irradiation. Tumour infiltrating into the surrounding normal tissue was observed by 60 days following irradiation. As the tumour regenerated, there was no accompanying regeneration of tumour capillaries. This study suggests that: a) tumour capillaries were more acutely radioresponsive than the normal microvasculature in the murine tail, and b) regenerating tumour did not elicit a neovascular response from the irradiated tumour bed.