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Institut de Protection et de Sûreté Nucléaire, Département de Protection de la Santé de l'Homme et de Dosimétrie, Section Autonome de Radiobiologie Appliquée à la Médecine, F-92265 Fontenay-aux-Roses Cedex, France
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
-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
Isc = 195.8 ± 14.7 µA/cm2,
n = 19, vs. 115.4 ± 8.2 µA/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.
muscarinic receptor; short-circuit current; rat ileum
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