Acute ingestion of dietary proteins improves post-exercise liver glutathione in rats in a dose-dependent relationship with their cysteine content.

Dietary sulfur amino acids affect glutathione synthesis, but their acute effect under conditions of oxidative stress is unknown. We assessed the effect of the selective ingestion of alpha-lactalbumin, a cysteine-rich protein, on glutathione homeostasis before a single bout of exhaustive exercise. One hour before a 2-h run on a treadmill, untrained rats ingested a meal enriched with either milk protein (TMP), alpha-lactalbumin-enriched milk protein (alpha-LAC), glucose (GLUC) or milk protein plus 150 mg N-acetyl-L-cysteine, a pharmacologic cysteine donor (NAC). Glutathione status was monitored in the blood and measured postexercise in the liver and heart. A group of fed sedentary rats was used as a control (CON). Blood total glutathione levels declined over time in all test groups. Although postexercise heart glutathione did not differ among groups, postexercise liver glutathione was curvilinearly related to prior cysteine intake (R2=0.999, P<0.05). In alpha-LAC rats, liver glutathione was 60-80% higher than in GLUC or CON rats (P<0.05) and did not differ from that of NAC rats. Cysteine from dietary proteins exhibits a considerable, dose-dependent and acute stimulatory effect on liver glutathione during exercise but does not immediately benefit whole-body glutathione homeostasis, presumably because of an overlap between the postprandial and exercise-related states.