Abstract
This study was conducted to determine the effects of different protein levels in diet on methylmercury intoxication and mercury accumulation in the organs when methylmercury was continuously administered in the diet to female Wistar rats for 15 months at a low dose level. Three kinds of basal diets were prepared : high-protein (53 % milk casein) diet, standard (20 % milk casein) diet and low-protein (5 % milk casein) diet. Three dose groups (20 animals in each) were structured in each of these basal diet groups : (1) control group, (2) 5 ppm methyl mercury chloride (MMC) group, (3) 5 ppm MMC+2 ppm sodium selenite (MMC+Se) group. Different levels of protein content in the diet did not change the growth rate of the animals, but administration of methylmercury considerably decreased the growth rate. Four rats from the MMC group in the low-protein diet developed neurogical signs of methylmercury poisoning (hindlegs-crossing and impairment of gait), whereas none of those signs were observed in animals from the MMC+Se group on the same low-protein diet. These facts suggest that a protein deficient diet causes toxicity of methylmercury to increase and selenium in the diet contributes to reducing the toxicity. There was no significant difference in total mercury accumulation in kidneys from the three groups with different protein levels, but the MMC group on the low-protein diet had the highest concentration of methylmercury in the kidneys. Total and methylmercury concentrations in brain and liver were at the highest levels in the low-protein diet groups and at the lowest levels in the high-protein diet groups. Moreover, the concentrations were higher in the MMC+Se groups than in the MMC groups.
