The stimulation and inhibition of the exhalation of volatile selenium

Administration of methylmercury (1.5-24 mumol kg-1; s.c.) to female rats simultaneously with Na2 75SO3 (0.25 or 24 mumol kg-1; s.c.) causes a dose-dependent increase in the exhalation of dimethylselenide. At the low selenite dose level, exhalation of 75Se over a 24 hr period is about fourfold greater after treatment with 24 mumol kg-1 methylmercury than that (approximately 0.75% of the dose) in the controls, but excretion by other routes (urine, faeces) and the liver and kidney contents of 75Se are not affected significantly. At the higher selenite dose level (24 mumol kg-1) exhalation of 75Se is correlated with the log dose of methylmercury. The faecal and urinary excretion remains essentially unaffected, and in rats treated with 24 mumol kg-1 methylmercury the 75Se contents of the liver, kidneys and blood are reduced by 78%, 86% and 18% respectively. The effects of the alkylmercurial are not specific since, at this selenite dose level, ethylmercury increases the exhalation and decreases the liver and kidney contents of 75Se approximately to the same extent as an equimolar dose of methylmercury. In methylmercury-treated and control animals dosed with 24 mumol kg-1 Na 75SeO3 the exhalation of 75Se is inhibited to the same extent by periodate-oxidized adenosine (PAD; 15 mumol kg-1, i.p.) in the first 6 hr. Later inhibition is less pronounced in methylmercury-treated rats. Under these conditions PAD has little effect on the renal content, but increases the hepatic content of 75Se. It seems, therefore, that the methylation of selenite occurs mainly in the liver and in both control and methylmercury-treated animals, S-adenosylmethionine is the major methyl donor. It is possible that methylmercury does not affect directly the methylation enzyme system but, by competition for protein sulphydryl groups, increases the availability of the intermediary selenide anion.