Protective effects of melatonin on γ-ray induced intestinal damage

Purpose: To examine the protective effects of melatonin on intestinal damage induced by gamma-rays. Materials and methods: Six-week-old Slc:ICR male mice were used. Mice were given whole-body irradiation at various exposure doses (7 - 21 Gy) with Cs-137 gamma-rays (0.98 Gy/min). The mice were orally administered 1 ml of either 1% carboxymethyl cellulose sodium salt (CMC) or melatonin (1, 5, 10 or 20 mg/ml) freshly prepared as a uniform suspension in CMC before or after irradiation. The concentrations of plasma melatonin were determined by the radioimmunoassay (RIA) method. The mice were killed at 3.5 days after the exposure. The jejunum was removed, fixed in formalin and then stained with hematoxylin and eosin. The numbers of crypts per transverse circumference were counted using a microscope for 10 histological sections of each mouse. Results: The intestinal damage caused by gamma-ray irradiation was prevented by melatonin correlating to dosage. The D-0 (slope of the dose-survival curve) value significantly (p < 0.05) increased from 1.55 +/- 0.19 (mean +/- SD) Gy to 1.98 +/- 0.16 Gy by orally administering 20 mg melatonin 30 min before irradiation. The radioprotective effect of melatonin continued for 6 h after the administration. Conclusions: Melatonin is judged to be a potential protector against intestinal damage associated with radiotherapy. Further experimental and clinical studies on this subject are needed to allow its use for radiotherapy.