A Comparison of Low and High Dose-Rate Radiation For Recipient Mice In Spleen-Colony Studies

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Abstract
Over the last 15 yr, endogenous spleen-colony formation in mice following lethal irradiation has increased to an unacceptable level. It has been found necessary, therefore, to introduce a new method of preparing recipient mice for spleen-colony studies. Irradiation with low dose-rate 60Cobalt .gamma. rays was compared with high dose-rate linear accelerator electrons, and their effects on endogenous spleen colony formation compared with earlier X and .gamma. ray dose-response data. A large dose (13.5 Gy [grays]) of .gamma. rays results in fewer endogenous colonies than 8.5 Gy of electorns, yet because of its low dose rate (14.1 .times. 10-3 Gy/min) it has a marked sparing of the intestinal tissue as measured by the intestinal microcolony technique. This in turn permits better survival and, therefore, a healthier animal for spleen-colony work. Exogenous colony formation is also lower in the low dose-rate, .gamma.-irradiated recipients and this is shown to be due to a reduced spleen-seeding efficiency. It is concluded that very low dose-rate radiation is preferable for hemopoietic ablation, that a mouse colony requires constant monitoring for changes of endogenous spleen-colony formation and that the spleen-seeding efficiency of CFU [colony forming units] depends on the irradiation technique used. There is no absolute value for a given strain of mouse.

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