CHRONIC EFFECTS OF METHYLMERCURY IN RATS .2. PATHOLOGICAL ASPECTS

Chronic effects of methylmercury (MeHg) were examined pathologically i n male Wistar rats fed on diet containing 0, 1 or 5 ppm Hg (as MeHg) f or two years. Organs including the central nervous tissues mere examin ed histopathologically using hematoxylin and eosin (H & E), Kluver-Bar rera (RE), PAS or phenol-congo red stains. The peripheral nerve system tissues mere also examined, using H & E and trichrome stains. Further more, immunoglobulins of renal specimens were demonstrated by direct i mmunofluorescence microscopy. Localization of mercury in the paraffin- embedded sections of the nervous tissue, kidney, liver, pancreas, sple en and testis was demonstrable by the photoemulsion histochemical meth od. In the 5 ppm group, mercury was readily detectable in tissues of t he rats exposed for one year, one and half years, two years and two an d half years. Mercury was detected in the cells of the brain such as n eurons, neuroglial cells, and phagocytes, and also in most organs, par ticularly in the epithelium of renal tubules, liver cells, myocardium, in the macrophages of pancreas, spleen and testis. In the 1 ppm group , mercury was detectable in the epithelium of renal tubules and liver cells. Fibrosis of the glomeruli was found in the rat group given a hi gh dose of methylmercury with all experimental methods. Granular IgG, IgM and C3 deposits mere demonstrated in the glomeruli by direct immun ofluorescence microscopy. The etiology of the pathological changes of glomeruli was suspected to be autoimmune glomerulopathy due to inorgan ic mercury filtration for a long time. It mas difficult to determine t he clinical signs and symptoms and pathological changes in the nervous system in spite of the deposition of mercury in the brain. (C) 1997 T ohoku University Medical Press.