Radiation dose-rate effects, endogenous DNA damage, and signaling resonance.

We previously concluded, from our analysis of the published data of other investigators, that the yield of germ-line and somatic mutations after exposure to ionizing radiation is parabolically related to the logarithm of the dose-rate at which a given dose is administered. Here we show that other data reveal a similarly parabolic relationship for other ionizing radiation-associated phenomena, namely, genetic recombination, chromosomal translocation, cell inactivation and lethality, and human leukemogenesis. Furthermore, the minima for all effects fall in a relatively narrow range of the dose-rate logarithms. Because the only mechanism common to all of these phenomena is the double-strand break (DSB) in DNA, we refer to our previous analysis of the endogenous production of DSBs, from which we concluded that approximately 50 endogenous DSBs occur per cell cycle, although most are repaired without error. Comparison then reveals that their rate of production falls within the range of minima for the several end points pursuant to radiation-induced DSBs. We conclude that the results reflect a physiological principle whereby signals originating from induced DSBs elicit responses of maximal effectiveness when they are produced at a rate near that of the production of endogenous DSBs. We refer to this principle as "signaling resonance."