Exposure to ionizing radiation alters vasoreactivity in rat jejunum ex vivo

The effect of ionizing radiation on jejunal blood flow was investigated in rats receiving whole-body exposure to 10 Gy gamma-radiation. Irradiation resulted in increased myeloperoxidase activity, indicative of neutrophil infiltration, and prostaglandin E2 synthesis by 2 h post-irradiation, but had no effect on leukotriene B4 synthesis. In ex vivo intestinal chamber studies, exposure to radiation reversed the mucosal-submucosal blood flow changes elicited by intravenous administration of leukotriene C4 (1 microgram.kg-1.min-1 for 10 min) or endothelin 1 (1 microgram.kg-1.min-1 for 5 min), but not that elicited by topical capsaicin (100 or 640 microM), as measured by laser Doppler flowmetry. The effect of radiation on vascular responses to leukotriene C4, but not those to endothelin 1, was reversed by pretreatment of the rats with the cyclooxygenase inhibitor, indomethacin (5 mg/kg). There was no significant effect of irradiation on mean arterial pressure or on ion or protein effluxes into the chamber bathing solution, nor did irradiation alter transmural potential difference. These studies point to altered responsiveness of the jejunal mucosal-submucosal vasculature shortly after exposure to ionizing radiation. Changes in function could reflect the onset of an acute inflammatory response, and appear to have cyclooxygenase-dependent and -independent components.