[Melatonin inhibits urethane-induced carcinogenesis tumors in murine lung]

Non-inbred SHR/u 3-month old mice were injected a single dose of urethane 1 g/kg, intraperitoneally. Beginning from day I after injection, they received melatonin 20 mg/l or 2 mg/l with drinking water at nighttime. After 28 days of the experiments, mice were sacrificed, lung adenomas counted and examined morphologically. Samples of blood and ling tissue were taken from each group and assayed for malonic dialdehyde (MDA) and catalase level. Tumor count of lung adenomas in the untreated group (control) was 23 +/- 2.63, melatonin 20 mg/l--14 +/- 1.2 (p < 0.01) and melatonin 2 mg/l--11 +/- 0.72 (p < 0.01). Urethane-treated mice revealed increased levels of MDA (62%) and catalase (70.7%) in blood-serum and in lung tissue (36.5%) as compared with control. Melatonin treatment significantly lowered concentrations of MDA in blood-serum and catalase (blood-serum and lung) rather than in the lung bearing urethane-induced tumor. Antitumor and antioxidant effect of relatively low dosage of melatonin appeared to be more effective than those of a larger one.