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Recent study has shown that a short photoperiod increases the accumulation and toxicity of cadmium (Cd) in the bank vole as compared to a long photoperiod. Since many of the effects of photoperiod on physiological processes in small mammals are transduced by the pineal gland and its hormone melatonin, in this study the effect of subchronic melatonin injection (7 micromol/kg/day for 6 weeks) on the hepatic, renal and intestinal Cd accumulation in the bank voles raised under a long photoperiod and exposed to dietary Cd (0.9 micromol/g) was examined. Simultaneously, histological examinations of the liver and kidneys, and analyses of metallothionein (MT) and lipid peroxidation were carried out. Melatonin co-treatment brought about a significant increase in the hepatic (61%), renal (79%) and intestinal (77%) Cd concentrations as compared to those in the Cd alone group. However, the concentrations of MT in the liver and kidneys of the Cd + melatonin co-treated bank voles did not differ from those in the Cd alone group. Also, histopathological changes in the liver (infiltration of leukocytes) and kidneys (glomerular swelling and a focal tubular cell degeneration) as well as an increase (2-fold) in the renal lipid peroxidation occurred only in animals from the Cd + melatonin group. These data indicate that (1) subchronic melatonin injection has similar effect on the tissue accumulation and toxicity of Cd to that produced by a short photoperiod and (2) the Cd-induced toxicity in the liver and kidneys of melatonin co-treated bank voles is probably due to increased Cd accumulation and decreased synthesis of MT.

Orally Administered Melatonin and the Accumulation and Toxicity of Cadmium in the Bank Vole (Myodes Glareolus)Animal gender and age significantly influence the accumulation and toxicity of heavy metals, including cadmium (Cd). The aim of this study was to determine the effect of orally administered melatonin (6 μg/ml), a known antioxidant and metal chelator, on Cd accumulation and toxicity in one month old females and males (young) and five months old bank voles (old) exposed to dietary Cd (100 μg/g) for six weeks. Compared to the Cd alone group, melatonin co-treatment brought about a decrease of Cd concentration in the liver (17% and 20%) and kidneys (39% and 36%) of young female and male bank voles, respectively, while in old animals increased Cd accumulation in liver (65%) and kidneys (81%) and enhanced consumption of Cd-contaminated food (136%) without any effect on their body mass. The results suggest that orally administered melatonin together with cadmium in young bank voles reduces tissue Cd accumulation possibly through forming stable complexes with this metal but in older rodents, melatonin increases concentration of the metal through increasing consumption of Cd-contaminated food.