Blood glutathione status during exercise: effect of carbohydrate supplementation.

Blood glutathione status and activities of antioxidant enzymes have been investigated during prolonged exercise with or without carbohydrate (CHO) supplementation. Eight subjects cycled at approximately 70% of maximal oxygen uptake to fatigue [134 +/- 19 (SE) min] on the first occasion (control, CON) and at the same work load and duration on the second occasion but with CHO ingestion during exercise. Blood reduced glutathione (GSH) concentration increased from 0.55 +/- 0.05 mM at rest to 0.77 +/- 0.09 mM after 120 min of exercise during CON (P < 0.01) but remained constant during CHO exercise. Blood glutathione disulfide (GSSG) levels were unchanged during CON and CHO exercise. Blood GSH + GSSG content and GSH/GSSG ratio were also significantly (P < 0.05) elevated during CON but not during CHO exercise. The increases in GSH and GSH + GSSG in CON were associated with decreases in plasma glucose and insulin levels. Activities of blood GSH peroxidase, GSSG reductase, and glucose-6-phosphate dehydrogenase were significantly increased during the CHO exercise, whereas only GSSG reductase activity was elevated during the CON ride. It is concluded that blood GSH increases during prolonged exercise and that CHO supplementation may prevent blood GSH increase possibly because of its inhibitory effects on hepatic hormonal releases, which stimulate GSH output.