The Effect of the iNOS Inhibitor S-Methylisothiourea and Hyperbaric Oxygen Treatment on Radiation Colitis in Rats

Introduction : External radiotherapy is one of the main treat- ment modalities for a variety of malignancies. However, the lower gastrointestinal tract is sensitive to the ionizing radiation. Hyper- baric oxygen treatment (HOT) has been suggested as a viable treat- ment for refractory radiation colitis, but the effect of S-Methyliso- thiourea (SMT) in the radiation colitis have not reported. Aim : To investigate the effect of SMT, HOT and the combina- tion of both in an acute radiation-induced enterocolitis model. Methods : Sixty Sprague-Dawley rats were divided randomly into five equal groups. A single dose of gamma irradiation (25 Gy) was administered through the colorectal region to anesthetized rats. In the control group, we applied 2 ml of saline solution intra- peritoneally for five days. In the HOT group, 100-per-cent oxygen at 2.5 atm pressure was applied for five days. In the SMT group, 10 mg/kg/day of SMT was applied intraperitoneally for five days. In the HOT+SMT group, HOT and SMT were both applied in the same dosages as in the preceding two groups. At the end of five days, the rats were sacrificed and colon samples were collected for histological grading. Blood samples were collected to test for : tu- mor necrosis factor-a (TNF-a), interleukin-10 (IL-10), IL-1ss, transforming growth factor-ss (TGF-ss) and intercellular adhesion molecule-1 (ICAM-1) mRNA.