Influence of aging and endurance training on lactate dehydrogenase in liver and skeletal muscle

The purpose of this investigation was to determine the effects of aging and endurance training on lactate dehydrogenase (LDH) activity and isozyme pattern in liver and skeletal muscle. Male Fischer 344 rats (n = 30) of three different age groups (young, 4 months; middle-aged, 12 months and old, 22 months) were trained on a treadmill at 75% running capacity for 1 h/day, five times per week for 10 weeks. Age-matched sedentary controls (n = 36) were used for comparison. Total LDH enzyme activity was measured spectrophotometrically; LDH isozymes were separated by native 5.5% polyacrylamide gel electrophoresis and quantified densitometrically. With increasing age, hepatic LDH activity decreased 28%. Old sedentary animals displayed significantly less (22%) hepatic LDH 5 than young and middle-aged animals, and significantly more (40%) hepatic LDH 4 than middle-aged animals. Training resulted in a significant decrease (38%) in total hepatic LDH activity in young rats only. Young animals displayed a significant increase in hepatic LDH 3 (28%), whereas middle-aged animals exhibited a significant decrease in hepatic LDH 3 (40%) with training. No change in total hepatic LDH activity was exhibited in middle-aged or old rats with training. Neither aging or training had a significant effect on LDH activity or isozyme pattern in extensor digitorum longus (EDL). Similarly, LDH activity was maintained in soleus with age, and isozyme pattern was only negligibly affected. We conclude that with age there is a decline in hepatic LDH activity and a decrease in the LDH 5 isozyme. Endurance training induced significant decreases in hepatic LDH activity of young animals. However, these decreases were not a result of shifts in isozymal pattern. Further, LDH activity was maintained in EDL and soleus muscle with age. Finally, endurance training did not have a significant effect on LDH activity or isozymal pattern of EDL or soleus.