Effect of sulfhydryl-deficient diets on hepatic metallothionein, glutathione, and adenosine 3'-phosphate 5'-phosphosulfate (PAPS) levels in rats.

Low dietary concentrations of methionine and cysteine are known to decrease hepatic glutathione content. However, it is not known if restricting the dietary content of these sulfur containing amino acids also affects hepatic levels of adenosine 3'-phosphate 5'-phosphosulfate (PAPS), the cofactor for sulfation, or metallothionein, a protein rich in sulfhydryl groups. Rats were fed diets lacking cysteine and containing various concentrations of methionine (0.15, 0.3, or 0.6%) for 8 days. Control diet contained 0.3% each of methionine and cysteine. Hepatic glutathione levels were decreased approximately 75% in rats fed diets containing 0.15 or 0.3% methionine. In contrast, PAPS and hepatic metallothionein concentrations were not decreased by the low sulfhydryl diets. Additionally, rats on the various diets were challenged by the administration of ZnCl2 (3 mmol/kg. sc). In both control rats and rats maintained on sulfhydryl-deficient diets, ZnCl2 increased hepatic metallothionein to the same level. However, significantly lower levels of PAPS were observed after ZnCl2 in rats receiving sulfhydryl-deficient diets than in controls. In summary, restriction of dietary sulfhydryl markedly decreases the hepatic content of glutathione and has a minor effect on PAPS concentration, but does not decrease the basal hepatic concentration of metallothionein or its induction by ZnCl2.