Mechanisms of Resistance and Reversal in the Initial Radiation Response in the Chick

Abstract

The comparison of split, fractionated, and protracted x-ray exposures on radiation mortality in the chick indicated the presence of qualitatively different processes operating between and during irradiations. Preliminary results suggested that a nonlinear process was the likely action between doses and that the induced resistance to subsequent irradiation might be dependent on the magnitude of the initial exposure. Further studies of the kinetics of processes operating both between and during exposures were carried out by using a challenging exposure as the technique for appraisal. Assessment of the differences between reversal and resistive processes is considered in so far as it contributes information concerning the mechanisms associated with the initial radiation response. Relationships between dose and time for mortality occurring after 2 days indicate that additional injury mechanisms contribute to the acute radiation sequelae. (C.H.)