Biphasic and triphasic dose responses in zebrafish embryos to low-dose 150 kV X-rays with different levels of hardness

The in vivo low-dose responses of zebrafish (danio rerio) embryos to 150 kv x-rays with different levels of hardness were examined through the number of apoptotic events revealed at 24 h post fertilization by vital dye acridine orange staining. our results suggested that a triphasic dose response was likely a common phenomenon in living organisms irradiated by x-rays,which comprised an ultra-low-dose inhibition,low-dose stimulation and high-dose inhibition. our results also suggested that the hormetic zone (or the stimulation zone) was shifted towards lower doses with application of filters. the non-detection of a triphasic dose response in previous experiments could likely be attributed to the use of hard x-rays,which shifted the hormetic zone into an unmonitored ultra-low-dose region. in such cases where the subhormetic zone was missed,a biphasic dose response would be reported instead. © 2016 the author 2016. published by oxford university press on behalf of the japan radiation research society and japanese society for radiation oncology.