INFLUENCE OF AGING AND ENDURANCE TRAINING ON LACTATE-DEHYDROGENASE INLIVER AND SKELETAL-MUSCLE

The purpose of this investigation was to determine the effects of agin g and endurance training on lactate dehydrogenase (LDH) activity and i sozyme 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 se dentary controls (n = 36) were used for comparison. Total LDH enzyme a ctivity was measured spectrophotometrically; LDH isozymes were separat ed by native 5.5% polyacrylamide gel electrophoresis and quantified de nsitometrically. With increasing age, hepatic LDH activity decreased 2 8%. Old sedentary animals displayed significantly less (22%) hepatic L DH 5 than young and middle-aged animals, and significantly more (40%) hepatic LDH 4 than middle-aged animals. Training resulted in a signifi cant 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 hepat ic 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 patter n in extensor digitorum longus (EDL). Similarly, LDH activity was main tained in soleus with age, and isozyme pattern was only negligibly aff ected. We conclude that with age there is a decline in hepatic LDH act ivity and a decrease in the LDH 5 isozyme. Endurance training induced significant decreases in hepatic LDH activity of young animals. Howeve r, these decreases were not a result of shifts in isozymal pattern. Fu rther, LDH activity was maintained in EDL and soleus muscle with age. Finally, endurance training did not have a significant effect on LDH a ctivity or isozymal pattern of EDL or soleus.