EXPOSURE TO IONIZING-RADIATION MODIFIES NEURALLY-EVOKED ELECTROLYTE TRANSPORT AND SOME INFLAMMATORY RESPONSES IN RAT COLON IN-VITRO

Purpose: To characterize the responsiveness of the colon to neural sti mulation following acute exposure of rats to gamma-radiation and to co rrelate observed changes to a number of parameters. Materials and meth ods: Rats were exposed to 5 or 10 Gy Cs-137 gamma- radiation or not (s ham-irradiated) and studied at 1, 3 and 7 days after irradiation. Stri pped segments of colon were mounted in Ussing chambers for measurement s of neurally-evoked electrolyte transport (electrical field stimulati on). Colonic tissue was also taken for biochemical (tissue 5-hydroxytr yptamine, histamine, leukotriene B-4, nitric oxide synthase) and histo logical analyses (mast cells).Results: In irradiated rats both proxima l and distal colon were hyporesponsive to electrical field stimulation at 1 and 3 days, but had recovered by 7 days. In the distal colon, ca rbachol responses were attenuated 1 day after 10 Gy. Mast cells, tissu e histamine and leukotriene B, synthesis were significantly reduced at all time points but no changes were seen in 5-HT or inducible NOS act ivity. Conclusions: Rat colon becomes hyporesponsive to neural stimuli post-irradiation. The response initially (1 and 3 days) correlates wi th decreased mast cells and histamine, but not at 7 days.