DL-methionine supplementation of rice-and-bean diets affects gamma-glutamyltranspeptidase activity and glutathione content in livers of growing rats

Gamma-glutamyltranspeptidase (GGT-EC 2.3.2.2) activity and glutathione (GSH ) content were measured in livers of female weanling Wistar rats (N = 5-18) , submitted to rice-and-bean diets (13 and 6% w/w protein), both supplement ed or not with DL-methionine (0.5 and 0.23 g/100 g dry diet, respectively). After 28 days, the rats on the rice-and-bean diets showed significantly hi gher levels (four times higher) of liver GGT activity and a concomitant 50% lower concentration of liver GSH in comparison with control groups feeding on casein. The addition of DL-methionine to rice-and-bean diets significan tly increased the liver GSH content, which reached levels 50% higher than t hose found in animals on casein diets. The increase in GSH was accompanied by a decrease in liver GGT activity, which did not reach levels as low as t hose observed in the control groups. No significant correlation could be es tablished between GGT and GSH changes under the present experimental condit ions. Linear correlation analysis only revealed that in animals submitted t o unsupplemented rice-and-bean diets GSH concentration was positively assoc iated (P<0.05) with weight gain, food intake and food efficiency. GGT, howe ver, was negatively correlated (P<0.05) with food intake only, and exclusiv ely for supplemented rice-and-bean diets. The high levels of GGT activity o bserved in the present study for rats receiving a rice-and-bean mixture cou ld be a result of the poor quality of these diets associated with their def iciency in sulfur amino acids. The results also suggest that diet supplemen tation with methionine could be important in the reduction of the deleterio us effects of GSH depletion by restoring the intracellular concentration of this tripeptide.