Inductive effects of methyl mercury on the hepatic microsomes of mice

Ultrastructural alterations of the liver of Pekin ducks fed methyl mercury-containing diets

This report describes the ultrastructural alterations of the liver of 24 male and 24 female Pekin ducks fed 0.0, 0.5, 5.0, and 15.0 ppm of methyl mercury chloride (MeHgCl), mixed in a mash diet, for 12 wk. Birds were weighed weekly and observed for neurologic symptoms daily. Samples of blood, liver, kidney, skeletal muscle and brain were analyzed for Hg residue by atomic absorption spectrophotometry. Livers were fixed in situ by perfusion with glutaraldehyde fixative and processed for electron microscopy. The percent decreases in mean body weights between wk 0 and wk 7 were statistically not significant except for males fed 5.0 ppm MeHgCl. Leg paralysis and convulsions in males treated with 15.0 ppm began at wk 5 and in females at wk 8, but were more severe in the latter. The dose-residue response for the three dose levels in all five tissues was linear, with liver and kidney containing the highest and the brain the least amount of Hg. Hepatocytes in 0.5- and 5.0-ppm MeHgCl treatment groups showed little morphologic changes, while liver cells in the 15.0-ppm group had several ultrastructural alterations, including remarkable increase in peribiliary lysosomal bodies. The mitochondria of some hepatocytes exhibited lysis of both inner and outer membranes. Changes also occurred in endothelial and Kupffer cells. These results indicate that dosing Pekin ducks with 15.0 ppm causes ultrastructural alterations indicative of toxic injury to the liver.

Methyl mercury decomposition in mice treated with antibiotics

The role of intestinal flora in the decomposition and faecal excretion of methyl mercury was studied in mice treated with antibiotics. The antibiotics, neomycin sulfate and chloramphenicol, were given to mice in drinking water for six days before intraperitoneal administration of methyl mercuric chloride (MMC), and intestinal microorganisms were thereby reduced. Inorganic and organic mercury were determined separately for faeces, intestinal contents and organs. On the fourth day after the mercury administration, the percentage ratios of inorganic mercury to total mercury in the contents of the caecum and large intestine were less in the mice treated with antibiotics, at 37% and 39%, respectively, than in the control mice (66% and 65%, respectively). Administration of the antibiotics reduced the excretion of inorganic mercury in the faeces to 26% of that of control mice and also reduced the excretion of total mercury to 60%. Reduction of intestinal microorganisms by the antibiotics was assumed to have caused the reduced decomposition of methyl mercury in the caecal contents and the reduced excretion of total mercury in the faeces.

Influence of mercury of the anesthetic response to and distribution of thiopental in rats

Pretreatment with HgCl2 (2 mg/kg sc) 24 h before administration of thiopental (35 mg/kg ip) significantly potentiated the duration of thiopental sleeping time in adult male rats but did not influence the onset time for anesthesia. The plasma concentration of free thiopental was significantly higher in the Hg-treated animals 15 and 45 min after thiopental injection (i.e., during the period of thiopental anesthesia), with a concomitant increase of the free thiopental concentration in the brain at 15 min. However, total and free brain thiopental concentrations in Hg-treated rats at the time of awakening were not different from those in saline-treated animals. Urinary thiopental remained unchanged from 0 to 2 h, but was increased in the treated urine from 0 to 27 h. In vitro studies showed a strong inhibition of thiopental binding in 24-h Hg-treated plasma. The results suggest that the prolongation of thiopental anesthesia induced by Hg pretreatment is probably related to changes in the disposition of thiopental in the plasma and brain rather than to an alteration in the sensitivity of the central nervous system.

Influence of protein deficiency on the inhibition of hepatic microsomal detoxication by methyl mercury in two rat strains

N- and C-oxygenation of N,N-dimethylaniline was studied in liver microsomes from 2 rat strains (Wistar, Strain R and Sprague-Dawley) subjected to protein deprivation and methyl mercury pretreatment, separately and in combination. A striking interstrain difference was observed. Strain R microsomes from 2 rat strains (Wistar, Strain R and Sprague-Dawley) subjected to tion, but little effect after methyl mercury pretreatment. With Sprague-Dawley microsomes, C-oxygenation was slightly reduced after both treatments. N-oxygenation was little affected in either strain. Methyl mercury treatment of protein deprived rats strongly inhibited C-oxygenation in microsomes from both strains, with N-oxygenation being unaffected in strain R microsomes whereas markedly reduced in microsomes from Sprague-Dawley.

Heavy metal toxicities

Several reviews have been published recently on the toxicity of heavy metals, but few of these have made any reference to the influence of the nutritional state of animals upon their tolerance of heavy metals. Furthermore, the clinical and metabolic changes occurring as a consequence of increased dietary intake of heavy metals are extremely dependent on factors such as the mineral composition of the diet and nature of the protein source. These aspects will be given particular attention in this review.