Adaptive Response of Human Lymphocytes to Low Concentrations of Radioactive Thymidine

TLDR

The study examines an adaptive response in lymphocytes similar to that seen with alkylating agents, where prolonged low‑dose exposure reduces damage from subsequent high‑dose exposure. Low‑level chronic radiation from [3H]thymidine reduced the yield of chromatid aberrations induced by subsequent x‑ray exposure, producing fewer aberrations than the additive expectation, a phenomenon observed across multiple fixation times and doses and absent with nonradioactive thymidine.

Abstract

When human lymphocytes were cultured with [3H]thymidine, which acts as a source of low-level chronic radiation, and then exposed to 150 rad of x-rays at 5, 7, 9, or 11 hours before fixation, the yield of chromatid aberrations was less than the sum of the yields of aberrations induced by [3H]thymidine and x-rays separately. Often fewer aberrations were found after exposure to radiation from both sources than were found after exposure to x-rays alone. At the same fixation times, nonradioactive thymidine did not affect the yield of x-ray-induced aberrations. The same phenomenon occurred at earlier fixation times, after exposure to 30 or 40 rad of x-rays and [3H]thymidine. This response is analogous to the adaptive response to alkylating agents whereby prior treatment with small doses for a long period reduces the damage occurring from large doses of similar agents given for a short time.