An evaluation of the impacts of aging on skeletal muscle performance in several mammalian divers
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Based on the ‘free radical theory of aging,’ I hypothesized that hypoxia caused by the mammalian dive response induces free radical production which could modulate or accelerate cellular aging. On the other hand, to prevent free radical “stress” (pro- /antioxidant imbalance), divers could display elevated protective mechanisms. Additionally, the unusual connection between diving physiology and foraging ecology implies that aging physiology is significant to our understanding of ecology for divers. This study examines three aspects of aging in representative diving mammals. First, gracilis muscle morphology was analyzed for old/young shrews (water shrew, Sorex palustris (diver); short-tailed shrew, Blarina brevicauda (non-diver)). Extracellular space was elevated in old animals (10% diver, ~70% non-diver; P=0.021), which corresponded to a larger extracellular collagen component of old muscle (~60%; P=0.008). Muscle was dominated by Type I collagen, and the ratio of collagen Type I: III more than doubled with age (P=0.001). Second, oxidative stress markers, protective antioxidant enzymes and apoptosis were examined in muscle of the two shrew species. The activities of antioxidant enzymes catalase and glutathione peroxidase were statistically identical at each age in both species. The Cu,Zn superoxide dismutase isoform was, however, elevated in older animals (115% diver, 83% non-diver, P=0.054). Only one indicator of oxidative stress (lipid peroxidation) increased with age (P=0.009), whereas the other markers declined (4-hydroxynonenal content, P=0.008, dihydroethidium oxidation, P=0.025). Apoptosis occurred in <1% of myocytes, and did not change with age. On balance, diving water shrews did not have adaptations to combat oxidative stress, yet they do not display excessive oxidative tissue damage. Apoptosis was similar between species. The third study component was the development of a predictive simulation model for the energetics of old/young foraging Weddell seals, Leptonychotes weddellii. With advancing age, the model predicts declining net energy gain associated with a decrease in muscle contractile efficiency. The effects of age are exacerbated when good prey patches are scarce. In such cases, declines in old seal energy gain caused by increased buoyancy and decreased aerobic dive limit become apparent. The model also addresses the idea that behavioral plasticity may allow older animals to compensate for age-related performance constraints.
Hindle, Allyson Gayle (2007). An evaluation of the impacts of aging on skeletal muscle performance in several mammalian divers. Doctoral dissertation, Texas A&M University. Available electronically from