[The gastrointestinal post-irradiation syndrome].

Abstract

In the recent years, more attention is paid by radiobiologists to both prevention and therapy of a relatively less studied gastrointestinal postirradiation syndrome (GPS). Moreover, the increase in interest in GPS is motivated with the requirement as to obtain the decrease in action of ionizing radiation on the intestinal mucosa at making radiotherapy of abdominal or pelvic region. The GPS occurs consequently to the affected abdominal region or all the organism with ionizing radiation. Its approximal doses from 10 to 100 Gy (gamma) are critical for the survival of intestinal mucosa, especially that of jejunum and ileum. Under the threshold of a single and total dose from 6 to 10 Gy, the intestinal mucosa may usually regenerate, and the survival depends mainly on the preservation or restoration of hemopoietic activity of blood forming tissues. The main pathogenetic GPS factor resides in the afflication of stem cells of mucosal crypts. The intestinal epithelium stops to be fluently replaced after the irradiation. The motion arrests of epithelial cells from crypts to the apex of villi. The elderly cells undergoes degradation, and after several days the denudation of mucosa occurs with possible distortion of deeper layers of intestinal wall. The intestinal microflora is involved in the pathogenesis both directly and indirectly. Amongst the former events is ranged the invasion of distorted mucosa in compromised both local and systemic immunity. Indirectly, the intestinal microflora is GPS associated by stimulating mitotic activity in crypts, therefore more cells are in the radiosensitive phase. In germ-free animals there is a significant decrease in mitotic activity of crypts, and the migration time of epithelial cells from crypts to the apex villi is twice more prolongated, what induces possible restoration of active center after the irradiation. The GPS also results in disorder of metabolic processes which are conditioned with intestinal mucosa. Its typical manifestation resides in the wash-out of mucus, decreased resorption of nutrients and loss of water and minerals into the intestinal lumen. The GPS-related are another disorders of the organism, those of liver and kidney apparently induced due to the intoxication with catabolic products. The microflora has been stated to be involved in GPS by the experiments on germ-free animals. In the absence of microflora, the survival is greater in duration. After a total pigs irradiation with 10-30 Gy, more than two times survival prolongation occurs. The abdominal irradiation with 12 Gy results to the death of only conventional pigs, whereas those germ-free show a survival.(ABSTRACT TRUNCATED AT 400 WORDS)