OBJECTIVE:To investigate the radioprotective effect of tea polyphenols (TP 50) against radiation-induced organ and tissue damage.METHODS:Beagle dogs were exposed to a single acute dose of whole-body y-radiation (3 Gy) and orally administered TP 50 (80 or 240 mg.kg-1.d-1) for 28 consecutive days.A hemogram was obtained from experimental dogs every other day for 42 d.At the end of the experiment,enzyme activities of the antioxidants superoxide-dismutase and glutathione peroxidase,serum levels of inflammatory cytokines (tumor necrosis factor-o,interleukin-1β,and interleukin-6),colony-forming units of bone marrow hematopoietic progenitor cells,and organ coefficients were measured.RESULTS:Dogs exposed to y-radiation alone exhibited typical hematopoietic syndrome.In contrast,irradiated dogs that received TP 50 exhibited an improved blood,profile with reduced leucopenia,thrombocytopenia (platelet counts),and reticulocyte levels.TP 50 also significantly elevated levels of the endogenous antioxidant enzyme superoxide-dismutase,reduced the increased levels of serum cytokine in response to radiation-induced toxicity,and increased colony-forming units of bone marrow hematopoietic progenitor cells.In addition,TP 50 repaired radiation-induced organ damage.CONCLUSION:The current findings suggest that oral administration of TP 50 to beagle dogs effectively alleviated hematopoietic bone marrow damage induced by y-radiation.