First report on the distribution of orally administered microcystin-LR in mouse tissue using an immunostaining method.

The purpose of this study was to investigate the distribution of microcystin-LR (MCLR) orally administered to mice using an immunostaining method. MCLR was orally dosed at 500 microg/kg to aged Balb/C and ICR mice and their lethality was 23.9%. The former was more sensitive to MCLR than the latter, suggesting that oral toxicity by MCLR is related to the animal strains tested, although the pathological and immunostaining changes were essentially the same in both strains. According to this method the distribution of MCLR and related compounds were indicated as the red staining. Particularly, livers of dead aged mice were intensively stained. The main route of absorption was considered to be the small intestine because the villi contained a large amount of MCLR in both surface epithelial cells and lamina propria, resulting in erosion. The absorbed MCLR was contained in blood plasma and moved to the liver, lung, and heart, and finally to capillaries of the whole body. Excretion of MCLR was shown in the mucous from goblet cells in both the small intestine and large intestine.