Acute exercise and skeletal muscle antioxidant and metabolic enzymes: effects of fiber type and age.

Inhibition of metabolic enzyme activity has been associated with free radical stress in locomotor muscle with prolonged or intense exercise. However, it is not known whether such alterations with acute exercise in skeletal muscle are influenced by muscle fiber type or age. Twenty 4-mo-old and twenty 24-mo-old female Fischer-344 rats were divided at random into young exercised (YE; n = 10), old exercised (OE; n = 10), young control (YC; n = 10), and old control (OC; n = 10) groups. Animals in both YE and OE groups ran on a treadmill (10% uphill grade) for 40 min at approximately 75% of each age-group's maximal O2 consumption. Immediately after the treadmill run, white gastrocnemius (WG), red gastrocnemius (RG), and soleus (SOL) muscles were removed and quick-frozen in liquid nitrogen. Malondialdehyde was significantly increased (P < 0.05) in RG of YE vs. YC rats. Glutathione peroxidase activity was significantly elevated (P < 0.05) in the WG of YE rats. Analysis of variance revealed a significant over-all increase in superoxide dismutase activity with exercise. Activities of phosphofructokinase (PFK), citrate synthase, succinate dehydrogenase, and 3-hydroxyacyl-CoA dehydrogenase were unchanged (P > 0.05) with acute exercise in the SOL. However, PFK activity was decreased in the WG by 60% in OE but only 33% in YE, and in the RG by 41% in OE but only 21% in YE. We conclude that maximal glycolytic flux in the gastrocnemius may be adversely affected by acute exercise, and this effect was more pronounced in the 24-mo-old group.