Functional changes in the rat distal colon after whole-body irradiation: Dose-response and temporal relationships

The aim of this study was to determine the acute radiation response of the rat distal colon by in vivo and in vitro measurements of the functions of t he colon over a range of radiation doses. Rats received a whole-body irradi ation of 2 to 12 Gy and were studied from 1 to 7 days after exposure. In vi vo water and electrolyte absorption was measured by insertion of an agarose cylinder in the colon of anesthetized rats. In vitro transepithelial elect rical parameters (potential difference, short-circuit current, transepithel ial conductance) were measured in Ussing chambers in basal and agonist-stim ulated conditions. In vivo and in vitro functional studies were completed b y standard histological analyses. The majority of functional modifications appeared at 4 days after exposure. At this time, a dose-dependent decrease in absorption of water and sodium/chloride ions in the colon was noted. In contrast, a twofold increase in potassium secretion was observed for every radiation dose studied. The response to secretagogues was attenuated at dos es >8 Gy. Modifications of basal transepithelial electrical parameters toge ther with marked histological alterations were observed at 4 days with the higher doses (greater than or equal to 10 Gy). In conclusion, these results show that functions of the colon are affected by irradiation and may contr ibute to diarrhea induced by ionizing radiation. (C) 2000 by Radiation Rese arch Society.