[The effects of dietary methionine and glycine on lead toxicity in choline-deficient chicks].

A 2×2×2 factorial experiment was conducted to study the effects of dietary methionine, glycine, and lead (Pb) in cholinedeficient chicks. The variables were: adequate or deficient methionine; adequate or excess glycine; and 0 or 1000 ppm lead (as Pb acetate 3H2O). Methionine stimulated growth when added to the methionine-deficient diets, but the response was greater when supplemental glycine was present. Addition of glycine to the glycine-adequate diets stimulated growth in the presence of adequate but not deficient methionine. The patterns of response to methionine were the same at both 0 and 1000 ppm dietary Pb. Added Pb depressed growth with all diets, but the depression was greater in methionine-deficient than in methionine-adequate diets. Hepatic nonprotein sulfhydryl (NPSH) and glutathione (GSH) concentrations were increased by both supplemental methionine and lead, and the effects were additive. Glycine levels did not significantly alter NPSH and GSH concentrations. Both methionine and glycine lowered Pb concentrations in kidney, and the effects were additive. The results are consistent with previous observations that added methionine ameliorates Pb-induced growth depression with choline-adequate diets, however, this effect is not as pronounced with choline-deficient diets. The results suggest (1) that glycine is limiting for growth in choline-deficient, methionine-adequate diets, and (2) that methionine and glycine may enhance Pb detoxification by different mechanisms.