Splenic, hepatic, renal and pulmonary clearance dysfunction associated with high-energy X-rays.

PURPOSE: To verify the high-energy X-rays effects on the blood clearance of colloidal particles by the spleen, liver, kidneys, and lungs. MATERIALS AND METHODS: Seventeen male Wistar rats were distributed into three groups. Group 1 (n = 5) - control - non-irradiated animals, group 2 (n = 6) - irradiated animals studied 24 h after irradiation, and group 3 (n = 6) - irradiated animals studied 48 h after irradiation. The animals were anesthetized and irradiated with a non-fractionated 8 Gy dose in the abdominal region divided into two parallel and opposite fields, 4 Gy was given to the anteroposterior and 4 Gy to the posteroanterior. This high dose of high-energy X-rays causes extensive cell killing, tissue disorganization and break down cell to cell communication. According to the groups, 50 µCi of technetium-phytate were injected into the right internal jugular vein. After 30 minutes, the liver, spleen, kidneys, and lungs were removed. The clot was harvested from the abdominal cavity two minutes after the sectioning of the abdominal aorta and cava vein. The organs and clot were placed into plastic flasks to be weighed and studied for the emission of radioactivity in a gamma radiation detector. The uptake function of each organ was calculated based on the count of gamma rays emitted per minute and normalized with the organ mass, having as a reference the radioactivity count of a standard sample. The arithmetic mean of each organ uptake was calculated and compared among the groups. RESULTS: After irradiation, the spleen uptake of colloidal radiopharmaceutical was greater, while the hepatic, renal, and pulmonary uptake were lower. The renal uptake decreased slower than the hepatic and pulmonary uptake. CONCLUSIONS: A single high dose of high-energy X-rays enhances the splenic clearance function, while it reduces the hepatic, renal, and pulmonary clearance until 48 h after irradiation, with a rapid deterioration of the hepatic and pulmonary uptake function.

Changes in splenic uptake pattern associated with X-ray irradiation.

PURPOSE: To evaluate the splenic uptake function after irradiation with high-energy X-rays. MATERIALS AND METHODS: Fourteen male Wistar rats were distributed into three groups. Group 1 (n = 6) - control, non-irradiated; Group 2 (n = 4) - animals that were irradiated and studied 24 h after irradiation; and Group 3 (n = 4) - animals that were irradiated and studied 48 h after irradiation. The animals were irradiated with 8 Gy X-rays in the abdominal region. According with the groups, after 24 or 48 h, 1 ml/kg of a 50% colloidal carbon solution was injected in the left internal jugular vein. After 40 min, the spleens were removed for histological studies. Macrophages containing carbon pigments in their cytoplasms were counted in 16 consecutive microscopic fields, and their means were considered as the uptake pattern of each animal. RESULTS: In the control groups, carbon pigments were captured by macrophages in the red and white pulps, while in the irradiated groups, the uptake in the marginal zone, around the white pulp, was enhanced. There was no disorder on the splenic parenchyma or necrosis in histological analyzes. Qualitatively rare apoptotic events were observed, with no difference between control and irradiated animals. CONCLUSION: The high-energy X-ray, used in radiotherapy, modifies the splenic clearance, enhancing the amount of marginal zone macrophages containing colloid particles. This radiation was not associated with morphological changes, nor with necrosis or apoptosis of splenic tissue.

Models of the radiation-induced bystander effect.

PURPOSE: To implement quantitative models of the Radiation-Induced Bystander Effects (RIBE) based on cellular excitation at a rate proportional to the concentration of signal molecules (called signals here) released by irradiated cells. Clonogenic cell survival and transformation frequency as a function of rescue time and dose were considered. MATERIALS AND METHODS: Our first stochastic model was based on the hypothesis that chemical signals are released into the extracellular medium by irradiated cells. These signals act on unirradiated cells switching them from the healthy to the dead state at rate R(t). We extended this model including a non-lethal transformed state in order to describe clonogenic cell survival and transformation frequency as a function of the number of alpha particles. RESULTS: The first stochastic model was applied to an experiment on human keratinocyte (HaCat) cells yielding the half-life of at least one signal among the ensemble of possible candidates to trigger cell death in this cell culture. The second model yielded good fits to the data on clonogenic cell survival and transformation frequency in microbeam experiments with mouse embryo (C3H10T(1/2)) cells (Sawant et al. 2001a, 2001b). CONCLUSIONS: The fit of the first stochastic model to HaCat cell survival yielded a half-life of the order of minutes for possible signal candidates. This model also furnished the variance of the fraction of surviving cells.