Expression, activity and cellular localization of inducible nitric oxide synthase in rat ileum and colon post-irradiation.
OBJECTIVE
Studies were conducted to determine the acute effect of exposure to ionizing radiation on inducible nitric oxide synthase (iNOS) activity and expression in the rat ileum and colon.


METHODS
Rats received whole body exposure to 10 Gy gamma-radiation and were studied 0.5-48 h later. Segments of ileum and colon were taken from anaesthetized rats for determination of myeloperoxidase activity (a marker of acute inflammation), and iNOS mRNA expression, enzyme activity and localization.


RESULTS
Myeloperoxidase activity in ileum was not increased compared with shams until 48 h post-irradiation. In colon, myeloperoxidase activity was lower than shams at 48 h post-irradiation. Irradiation resulted in a dexamethasone-sensitive expression of iNOS mRNA in both the ileum and colon within 2h. Inducible NOS activity was significantly elevated in the ileum, but not in the colon. The elevated ileal nitric oxide synthase activity was significantly reduced by pretreatment with the iNOS inhibitor, aminoguanidine. Immunoreactivity for iNOS protein was localized to the epithelium and was apparent at 2-6 h post-irradiation in the ileum, but not the colon.


CONCLUSIONS
Exposure to ionizing radiation results in the expression of iNOS in ileum and colon, but only significantly increases iNOS activity in the ileum. Inducible NOS-derived NO may participate in acute, whole body radiation-induced ileal dysfunction, independently of the development of an inflammatory response.
Department of Physiology and Biophysics, University of Calgary, Canada. wmacnaug@acs.ucalgary.ca
W K
WK
MacNaughton
A R
AR
Aurora
J
J
Bhamra
K A
KA
Sharkey
M J
MJ
Miller
D000818:Animals; D001120:Arginine / Q000378:metabolism; D002588:Cesium Radioisotopes; D005720:Gamma Rays / Q000009:adverse effects; D015971:Gene Expression Regulation, Enzymologic / Q000528:radiation effects; D006146:Guanidines / Q000494:pharmacology; D007150:Immunohistochemistry; D007249:Inflammation / Q000503:physiopathology; D007422:Intestines / Q000201:enzymology* / Q000528:radiation effects*; D009569:Nitric Oxide / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000378:metabolism*; D052247:Nitric Oxide Synthase Type II; D009195:Peroxidase / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D011839:Radiation, Ionizing; D051381:Rats; D014916:Whole-Body Irradiation
D002588:Cesium Radioisotopes; D006146:Guanidines; D012333:RNA, Messenger; D009569:Nitric Oxide; D001120:Arginine; D009195:Peroxidase; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; C496318:Nos2 protein, rat; C004479:pimagedine