EXPOSURE TO IONIZING-RADIATION ALTERS VASOREACTIVITY IN RAT JEJUNUM EX-VIVO

The effect of ionizing radiation on jejunal blood flow was investigate d in rats receiving whole-body exposure to 10 Gy gamma-radiation. Irra diation resulted in increased myeloperoxidase activity, indicative of neutrophil infiltration, and prostaglandin E(2) synthesis by 2 h post- irradiation, but had no effect on leukotriene B-4 synthesis. In ex viv o intestinal chamber studies, exposure to radiation reversed the mucos al-submucosal blood flow changes elicited by intravenous administratio n of leukotriene C-4 (1 mu g . kg(-1). min(-1) for 10 min) or endothel in 1 (1 mu g . kg(-1). min(-1) for 5 min), but not that elicited by to pical capsaicin (100 or 640 mu M), as measured by laser Doppler flowme try. The effect of radiation on vascular responses to leukotriene C-4, but not those to endothelin 1, was reversed by pretreatment of the ra ts with the cyclooxygenase inhibitor, indomethacin (5 mg/kg). There wa s no significant effect of irradiation on mean arterial pressure or on ion or protein effluxes into the chamber bathing solution, nor did ir radiation alter transmural potential difference. These studies point t o altered responsiveness of the jejunal mucosal-submucosal vasculature shortly after exposure to ionizing radiation. Changes in function cou ld reflect the onset of an acute inflammatory response, and appear to have cyclooxygenase-dependent and -independent components.