Pharmacological Aspects of the Vascular Permeability Changes in the Rat's Intestine Following Abdominal Radiation

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Abstract
Irradiation of the abdomen of rats was followed by increased capillary permeability of the intestine to circulating protein-bound trypan blue; these changes are clearly visible 24 hours after X irradiation, and are maximal by 72–96 hours. Pre-treatment of the rats with antihistaminics caused a marked suppression of the vascular changes during the first 24 hours, but has no subsequent effect. During the first 24 to 48 hours the ileum was almost completely depleted of histamine and 5 H.T. The increased capillary permeability normally observed from 48 hours onwards could be markedly reduced by prior treatment of the animals with various anti-esterase drugs. It is postulated that following irradiation of the abdomen, the increased capillary permeability of the intestine is mediated initially by histamine and then maintained by an enzyme system involving a protease or esterase.