A comparison of glycogen, glucose-6-phosphate dehydrogenase, and citrate synthase levels in previously untrained young and adult rats following an exhaustive swim

Many of the physiological responses concomitant with exercise are understood. Similarly, many of the changes characterizing the aging process have been established. However, the combination of the two (ie. effects of aging on exercise or vice versa) presents a myriad of questions, of which many remain unanswered.The objective of this study was to establish the differences between previously untrained young and adult male Fischer 344 rats following an exhaustive swim for the following parameters: 1) muscle glycogen, an essential fuel substrate; 2) Glucose-6-phosphate dehydrogenase (G6PDH), a marker of inflammation and tissue damage; 3) citrate synthase (CS), an integral enzyme of the Kreb's cycle and a respiratory chain marker; 4) muscle protein; and 5) percent muscle dry weight.The rats were divided into two groups by age. Young (3 mo., n=16) and adult (12 mo., n=17) rats were randomly divided into sedentary (young sed (YSD) n=7 and adult sed (ASD) n=9) or exercised groups (young swimmers (YSW) n=8 and adult swimmers (ASW) n=8). Rats in the swimming groups were given a brief exposure to the water one week prior to their exhaustive swim to minimize the stress and confusion during the actual exercise bout. On the study days one randomly selected swimmer from each age group was swum to exhaustion and sacrificed via pneumothorax. One animal from each of the respective sedentary age groups was also randomly selected and sacrificed as above. The plantaris, rectus femoris, red vastus, soleus, triceps, and liver were surgically excised from each animal and frozen in liquid nitrogen for later analysis.While the younger animals had lower glycogen stores initially, following the exhaustive swim their reduction in muscle glycogen was approximately 150% that of the adult animals for any given muscle. Muscle glycogen levels in ASD and YSD rats were significantly higher than those of the YSW animals for all muscles with the exception of the YSD's soleus. However, the percent decrease in liver glycogen following the swim for the two age groups was almost identical (a reduction of 55.05% and 58.59% for the adult and young age groups, respectively).Although the adult animals were significantly heavier than the younger rats, this did not appear to cause a significant difference in their swim time to exhaustion. No significant differences were observed between the groups for muscle protein or G6PDH. Levels of CS were significantly higher in the YSD plantaris when compared to the ASW. Similarly, the ASD rectus femoris CS levels were significantly greater than those of the ASW. Although significant differences between groups in percent muscle dry weight existed for the plantaris, rectus femoris, and triceps such differences seemed to have little bearing on the two age group's swim to exhaustion times.On the basis of this study it was concluded that although starting with greater glycogen stores prior to exercise, adult animals use less of this substrate prior to exhaustion than do younger animals. While the mechanism for such a phenomenon was not discovered it is believed to be enzymatic in nature. Furthermore, the adult animals do not appear to exhibit significantly more tissue damage following an exhaustive swim than that seen in younger animals.School of Physical EducationThesis (M.S.