The effects of chronic oral methyl mercury exposure on the lysosome system of rat kidney. Morphometric and biochemical studies.

This report describes morphometric and biochemical changes in the renal lysosome system of rats exposed to 3, 5, or 10 p.p.m. concentrations of methyl mercury hydroxide in their drinking water for 4 weeks. Increased numbers of dense, granular lysosomes, previously found to contain mercury, were observed in tubule cells of rats receiving the 3 and 5 p.p.m. dose levels but not those of the 10 p.p.m. group. Tubule cells from animals given the 10 p.p;m. dose level displayed proteinaceous vacuoles with dense crystalloid structures, apical cytoplasmic extrusion, and cellular degeneration; Mitochondrial swelling within tubule cells of treated animals showed a marked dose-response relationship. Renal microsomal activity levels of ss-glucuronidase were strongly inhibited by methyl mercury hydroxide exposure at all dose levels, whereas the activity levels of acid phosphatase were unchanged. Lysosomal beta-glucuronidase was also inhibited by methyl mercury hydroxide exposure, whereas lysosomal acid phosphatase showed approximately a 2-fold increase in activity. The results are discussed in relation to the role of lysosomes in mediating the nephrotoxic effects of methyl mercury and other toxic trace metals.