The Effects of Age and Acute Submaximal Exercise on Metabolic and Hormonal Characteristics of Hamsters.

The purpose of this study was to examine metabolic, hormonal and running characteristics of senescent hamsters to determine if hypoactivity in old hamsters is related to age differences in substrate availability or utilization during exercise. We compared spontaneous running patterns and treadmill performance in young-adult control (2-3 month old) and old (16-17 month old) female hamsters. Addi- tionally, we measured concentrations of substrates and hormones in the serum and substrates in liver and quadriceps at 0 and 60 minutes of treadmill running at 60 percent of peak (')VO(,2), and following an epi- sode of approximately two hours of voluntary running on horizontal discs. The total amount of spontaneous running in old hamsters, as well as duration of individual bouts was approximately 50 percent of that in young animals, while aerobic capacity and endurance per- formance declined with age by only 13 and 27 percent, respectively. At rest, compared to young hamsters, quadriceps glycogen concen- tration was elevated in old, while hepatic glycogen concentration was depressed. No age differences in intramuscular triglyceride, serum free fatty acids or glycerol were observed. Serum glucose concentra- tion was elevated in non-exercised young hamsters, while the con- centration of serum glucagon was elevated in old animals. Serum insulin concentration was depressed in non-exercised old animals in the treadmill experiment, but not in the voluntary running experiment. Liver glycogen concentration decreased in young animals with both voluntary and treadmill exercise, but was unchanged in old exercised animals. Quadriceps glycogen depletion was similar in both groups with treadmill exercise, but was greater in old animals during volun- tary running. Neither exercise protocol had an effect on quadriceps triglyceride. Free fatty acids and glycerol concentrations were similar in young and old animals during both experiments. Under conditions of non-limiting substrates and cofactors, oxidative capacity was approximately 35 percent lower in both cardiac and skeletal muscle homogenates from old animals with palmitoyl-carnitine as substrate, but not with pyruvate-malate. These data may indicate an age dec- rement in the carnitine transport mechanism or some step in (beta)-oxidation, with no age effect on steps in the tricarboxylate cycle or electron transport. These data indicate that: (1) substrate availa- bility is not a limiting factor in endurance running in old hamsters, (2) factors other than those that limit aerobic capacity and endur- ance performance are responsible for the age decrement in spontaneous running in this species.PhDAnimal PhysiologyPhysical educationUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/160845/1/8600514.pd