Late effects of successive massive doses of radiation on parabiont rat pairs.

Parabiosis of rats permits one partner to survive 1000 R X-radiation if the other is shielded. This dose to the previously shielded partner after intervals of 5, 10 or 30 days tests the ability of the first irradiated partner to recover and, in turn, support the second. The effectiveness of this can be measured by the late effects induced in the pair. Lifespan was shortened by 100--150 days following a 5-day interval, by 30 days following a 10-day interval and not shortened following a 30-day interval. The incidence of leukaemia was about 6 per cent in each group, close to that in control pairs. Shortening the interval between the irradiations decreased the average age of death from leukaemia. No solid lymphoid tumours were induced in the doubly irradiated pairs. The incidence of osteogenic sarcoma was 1.6 per cent in controls and 12.9 per cent in the pairs with both partners irradiated.