Initial Steps in Development of Rat Genetic Models for the Response to Exercise Training
S.L. Britton, M.L. Troxell, L.G. Koch
Medical College of Ohio, Toledo, OH
Evidence suggests that two types of genetic substrates influence aerobic capacity. First, there is a complement of genes that determine intrinsic capacity in the untrained state. On top of intrinsic capacity is apparently another set of genes that dictate the response to exercise. We recently developed rat genetic models of intrinsic aerobic capacity by artificial selection. Our next goal is to create rat genetic models for the response to training.
PURPOSE: As initial steps, we tested: 1) If wide variation exists for the response to training in a genetically heterogeneous population of rats (N:NIH stock), and 2) If intrinsic aerobic capacity and the response to training are correlated phenotypes.
METHODS: Forty rats were first tested for intrinsic aerobic capacity by measuring distance run to exhaustion on a treadmill using a ramped protocol. Each rat was then trained for treadmill running 3-days per week for eight weeks. An absolute training protocol was used so that the same environment was applied to all rats. The training protocol started at a speed of 10 m/min for 20 min at a 15¡ grade and was gradually increased daily in speed and duration to reach 16 m/min for 30 min. A post-test for maximal treadmill running capacity was performed at week 9. The response to training was taken as the difference in distance run to exhaustion before and after training.
RESULTS: Differences in pre- and post tests for treadmill running to exhaustion (delta meters run) were highly variant and ranged from -72 meters to +430 meters. The distribution of these data was not different from normal (P > 0.169). Data demonstrated no correlation between pre-trained intrinsic aerobic capacity (meters) and the response to treadmill training (delta meters) (r = 0.242, P< 0.132).
CONCLUSIONS: These data demonstrate a sufficiently wide selection differential for the adaptational response to training to support the initiation of divergent selective breeding from a large founder population. In addition, these data are consistent with the idea that intrinsic aerobic capacity and the adaptational response to training are determined by separate genetic substrates (i.e., not correlated).
[Supported by the National Institutes of Health (HL64270)]