## 1 Introduction  
Threats of terrorist attacks, expanding nuclear industry, widespread utilization of ionizing radiation in many technologies are potentially exposing the world population to ongoing and new radiation threats.  
Therefore, there is an urgent need for developing new Acute Radiation Syndrome (ARS) prevention and treatment strategies. Currently, USA Food and Drug Administration (FDA) approved colony-stimulating factors such as Neupogen, Neulasta, Leukine and thrombopoietin receptor agonist NPLATE to treat those who have received high doses of radiation [1]. These drugs, used also in cancer patients receiving myelosuppressive chemotherapy, accelerate the process of creating white blood cell, boost platelets (NPLATE) and reduce the time that the patient is vulnerable to infection and blood coagulation disorders.  
A good medical countermeasure (MCM) for radiation exposure should be easy to handle, safe, stable (under extreme conditions), cheap, deployable and must meet the medical need for rapid therapeutic support including non-radiation medicine [2]. Activatedcharcoal (AC) for medical use from this point of view seems to be ideal MCM. AC successfully increased animals' survival from 3.2% in control group to 68.1% when administered during 24 h after irradiation in experiment for hemoperfusion treatment of dogs irradiated with lethal doses of X-ray [3]. Oral administration of AC alone (or in combination with granulocyte colony-stimulating factor in pre-clinical and clinical trials) after Irradiation or anticancer chemotherapy reduced intoxication, prevented and treated leukopenia [4].  
The National Security Hospital after the Chernobyl disaster reported 10 years' experience in hemo- and enterosorption application of AC in the effective treatment of post-irradiation injuries in patients [5]. AC showed high adsorption capacity towards toxic substances that appear in different pathological states, particularly in ARS. AC with high adsorptive capacity effectively removes cytokines of different size (IL-6 and IL-8), protein-bound molecules (hippuric acid and indoxyl sulfate) and middle-sized molecules, such as \(\beta\)-2-microglobulin [6]. AC mitigates manifestation of oxidative stress, contributes to restoration of natural detoxification potential of organism through deliganding serum proteins (in particular--albumin) from endogenous metabolites and toxins [7].  
ARS is the result of direct and indirect mechanisms of ionizing radiation action on cells. Reactive oxygen species, proinflammatory cytokines/chemokines and induction of gene expression provoke oxidative damage, inflammation, innate immune response leading to cell death and damage [8; 9]. These indirect damage effects of ionizing radiation can probably be reduced by AC, that removes cytokines, protein-bound substances, middle-sized molecules and endogenous metabolites from biological fluids. Radiation leads to multiple organ dysfunction syndrome and life-threatening multiple organ failure [9]. It provokes severe damage in gastrointestinal system [10] and brain [11]. Bone marrow or hematopoietic syndrome is the most classically recognized ARS. Relatively low levels of exposure can result in bone marrow failure, potentially lethal hemorrhage or infections [12]. In the present work, we aimed to investigate the potential of the newly developed orally administered highly activated charcoal as a possible ARS medical countermeasure. Effect of AC on reducing weight loss, ionizing radiation-induced injury in hematopoietic tissue, small intestine, spleen, thymus and superoxide ion generation in the brain and liver was evaluated in rats after total body X-ray irradiation in sublethal dose.