Alteration of Intestinal Vasoactivity during the Development of the Gastrointestinal Radiation Syndrome
ARMED FORCES RADIOBIOLOGY RESEARCH INST BETHESDA MD
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The functional vascular integrity of the small intestine in relationship to its morphological alterations during the post irradiation period was examined Dogs were exposed to 1500 rads midline tissue dose of mixed gamma-neutron radiation. Hemodynamic parameters of an in situ intestinal loop were measured in response to the systemic administration of norepinephrine, isoproterenol and gradual bleeding and reinfusion. The results indicate that 48 hours postirradiation when the capillaries are virtually intact and the systemic hemodynamic parameters are not altered yet, the functional integrity of the intestinal vasculature is already significantly deteriorated. The intestinal resistance vessels of the irradiated animals did not exert autoregulatory escape as the controls did. After 72 hours the vasocompensation to the sudden blood pressure changes was also markedly changed. The fluctuation of the intestinal resistance values during the bleeding and reinfusion periods demonstrated neurohumoral imbalance in the postirradiation period. On the basis of these results it is postulated that the terminal cardiovascular collapse in irradiated animals might be due to the development of intestinal ischemic shock.