Ionizing radiation stimulates muscarinic regulation of rat intestinal mucosal function
Lebrun F, Francois A, Vergnet M, Lebaron-Jacobs L, Gourmelon P, Griffiths NM.
Am J Physiol 1998 Dec;275(6 Pt 1):G1333-40
The aim of this study was to determine whether ionizing radiation modifies muscarinic regulation of intestinal mucosal function. Rats exposed to total body 8-Gy gamma-irradiation or sham irradiated were studied up to 21 days after irradiation. Basal and carbachol-stimulated short-circuit current (Isc) and transepithelial conductance (Gt) of stripped ileum were determined in Ussing chambers. Muscarinic receptor characteristics using the muscarinic antagonist [3H]quinuclidinyl benzilate and three unlabeled antagonists were measured in small intestinal plasma membranes together with two marker enzyme activities (sucrase, Na+-K+-ATPase). Enzyme activities were decreased 4 days after irradiation (day 4). Basal electrical parameters were unchanged. Maximal carbachol-induced changes in Isc and Gt were increased at day 4 (maximal DeltaIsc = 195.8 +/- 14.7 microA/cm2, n = 19, vs. 115.4 +/- 8.2 microA/cm2, n = 63, for control rats) and unchanged at day 7. Dissociation constant was decreased at day 4 (0.73 +/- 0.29 nM, n = 10, vs. 2.14 +/- 0.39 nM, n = 13, for control rats) but unchanged at day 7, without change in binding site number. Thus total body irradiation induces a temporary stimulation of cholinergic regulation of mucosal intestinal function that may result in radiation-induced diarrhea.