Prospects for management of gastrointestinal injury associated with the acute radiation syndrome.

The effect of total-body ionizing radiation on the digestive tract is dose-dependent and time-dependent. At low doses (1.5 Gy), one observes only a short prodromal syndrome consisting of nausea, vomiting, and gastric suppression. At doses greater than 6 Gy, the prodromal syndrome is more marked, and it is followed after a 2-5-day remission period by a subacute syndrome, characterized by diarrhea and hematochezia. This gastrointestinal syndrome is superimposed onto a radiation-induced bone marrow suppression. The combination of intestinal and hemopoietic syndromes results in dehydration, anemia, and infection, leading eventually to irreversible shock and death. The treatment of prodromal symptoms is based on the administration of antiemetics and gastrokinetics, although an effective treatment devoid of side effects is not yet available for human therapy. The treatment of the gastrointestinal subacute syndrome remains difficult and unsuccessful after exposure to total body doses greater than 8-10 Gy. Supportive therapy to prevent infection and dehydration may be effective if restoration or repopulation of the intestinal and bone marrow stem cells does occur. In addition, bone marrow transplantation may improve the prospect of treating the hemopoietic syndrome, although the experience gained in Chernobyl suggests that this treatment is difficult to apply in the case of nuclear accidents. Administration of radioprotectants before irradiation decreases damage to healthy cells, while not protecting cancerous tissues. In the future, stimulation of gastrointestinal and hemopoietic progenitor cells may be possible using cell growth regulators, but much remains to be done to improve the treatment of radiation damage to the gastrointestinal tract.