STUDIES ON THE BIOLOGICAL EFFECTS OF YTTRIUM - EFFECTS OF REPEATED ORAL-ADMINISTRATION TESTS IN RATS

In order to elucidate the series of the biological effect of the rare earth elements, a 28-d repeated oral administration test was conducted in Slc : Wistar rats of each sex by gavage at doses of 0, 40, 200 or 1000 mg/kg/d of YCl3.6H2O with the pair feeding group. Additionally two more groups (0 mg/kg, 1000 mg/kg) of both sexes were maintained for a 14-d recovery period after the 28-d administration. Body weight and food consumption were measured, and hematological, serum-biochemical and histopathological examination were performed. The concentrations of yttrium and essential elements in organs were determined by ICP-MS or ICP-AES. These overall data on yttrium were compared with our previous study on lanthanum performed by the same protocol. The results were as follows. (1) The number of eosinophilic leucocytes increased in rats of both sexes dose-dependently. (2) At a dose of 1000 mg/kg, hyperkeratosis in the forestomach of both sexes, eosinophilic leucocyte infiltration in the submucosa of the stomach of both sexes, erosion and dilatation of gastric gland of the glandular stomach in males, and swelling of the glandular stomach epithelium in females were found. These results suggest that yttrium is irritant to the stomach mucosa. (3) At doses higher than 200 mg/kg, a significant decrease of the serum cholinesterase activity was observed in females. (4) At the 1000 mg/kg lanthanum-dosed rats of our previous study, the serum transaminase activity increased in both sexes. On the other hand, there were no changes between control and yttrium-dosed rats. (5) Yttrium was accumulated in the kidney, femur, liver and spleen, in a dose-dependent manner. (6) The highest accumulation of yttrium was found in the kidney. According to the previous lanthanum study, the highest accumulation of lanthanum was observed in the liver. (7) The total amount of yttrium accumulation in rats was about 50 times as much as that of lanthanum. (8) The sex-dependent differences were observed in terms of the irritating reaction of the stomach mucosa, the reduction of the serum cholinesterase activity and the accumulation of yttrium in the kidney. (9) These results show that yttrium could be absorbed through the digestive tract. (10) Iron concentrations in the liver, kidney and spleen, and barium and strontium concentrations in the femur were dose-dependently decreased in both sexes of yttrium - treated rats. Both yttrium and lanthanum are classified as rare earth elements and the present study revealed that the biological effects of yttrium were very similar to those of lanthanum except the accumulating patterns and volumes. On the other hand, in contrast to the fact that lanthanum was hepatotoxic compound, yttrium had no effect on liver, which seems to be due to the difference of their accumulating patterns.