MicrocystinLR (MCLR), a cyclic heptapeptide produced by the bluegreen algae Microcystis aeruginosa, produces death in female mice treated with 100 ?g MCLR/kg. Kupffer cell hyperplasia was observed histologically after treatment with 50 or 100 gg MCLR/kg. No other changes or lethality were observed with the 50 ng MCLR/kg, while 100% lethality occurred in less than 2 h in mice treated with 100 ?g/kg. In these animals liver weights increased by 45% and hepatic hemoglobin content increased 106% at 60 min posttreatment. Liver histology showed loss of hepatic architecture and necrosis 30 min after treatment, and congestion with blood became evident at 45 min after treatment. Serum enzymes were significantly increased 45 min posttreatment. Hepatic nonprotein sulfhydryl content decreased 19% when calculated on the basis of cytosolic protein and 39% when based upon the total protein content, respectively. The sulfhydryl content of the liver cytoskeletal fraction decreased 26% by 30 min after treatment. Decreased enzymemediated and increased nonenzymemediated lipid peroxidation were observed in hepatic microsomes following both in vivo and in vitro exposure of hepatic microsomes to MCLR. The toxicity of MCLR may be related to alterations in the sulfhydryl content of the cytoskeletal protein. Furthermore, MCLR may either directly or indirectly affect microsomes, suggesting alterations in structure and function of smooth endoplasmic reticulum.
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