EXPOSURE TO IONIZING-RADIATION INCREASES RESPONSIVENESS TO NEURAL SECRETORY STIMULI IN THE FERRET JEJUNUM IN-VITRO

Experiments were designed to determine the effects of ionizing radiati on on jejunal epithelial function in the ferret in vitro. Basal and st imulated electrolyte transport were determined in Ussing chambers at 0 .5, 2, 24 and 48 h post-irradiation. Tissue histamine and 5-hydroxytry ptamine levers were measured. Myeloperoxidase activity wats also measu red as an index of inflammation. Basal short circuit current was reduc ed at 2 h post-irradiation, but was elevated at 48 h. Basal conductanc e was significantly increased by 24 and 48 h. Responsiveness to electr ical field stimulation was depressed at 0.5h, and was greater than con trol by 24 and 48 h post-irradiation. Similarly, short circuit current responses to prostaglandin Eg were depressed at 0.5 h and elevated at 24 h. No significant change was observed in the response to carbachol post-irradiation, indicating that alterations in responsiveness were not likely at the level of the enterocyte. Changes in responsiveness t o electrical field stimulation correlated significantly with increases in mucosal mast cell numbers. Myeloperoxidase activity, indicative of neutrophil infiltration, did not increase post-irradiation, nor was t here histological evidence of an inflammatory cell infiltrate. There w ere no changes in tissue histamine or 5-hydroxytryptamine Histology al so revealed little microscopic morphological change from shams in tiss ue from irradiated ferrets. The results of this study demonstrate effe cts of irradiation on electrolyte transport in the ferret jejunum. The enhanced neurally evoked electrolyte transport observed at 24-48 h po st-irradiation was not correlated with the development of inflammation , but was correlated with changes in mast cell numbers.