title: Exhaustive exercise training enhances aerobic capacity in American alligator (Alligator mississippiensis).
abstract: The oxygen transport system in mammals is extensively remodelled in response to repeated bouts of activity, but many reptiles appear to be 'metabolically inflexible' in response to exercise training. A recent report showed that estuarine crocodiles (Crocodylus porosus) increase their maximum metabolic rate in response to exhaustive treadmill training, and in the present study, we confirm this response in another crocodilian, American alligator (Alligator mississippiensis). We further specify the nature of the crocodilian training response by analysing effects of training on aerobic [citrate synthase (CS)] and anaerobic [lactate dehydrogenase (LDH)] enzyme activities in selected skeletal muscles, ventricular and skeletal muscle masses and haematocrit. Compared to sedentary control animals, alligators regularly trained for 15 months on a treadmill (run group) or in a flume (swim group) exhibited peak oxygen consumption rates higher by 27 and 16%, respectively. Run and swim exercise training significantly increased ventricular mass (~11%) and haematocrit (~11%), but not the mass of skeletal muscles. However, exercise training did not alter CS or LDH activities of skeletal muscles. Similar to mammals, alligators respond to exercise training by increasing convective oxygen transport mechanisms, specifically heart size (potentially greater stroke volume) and haematocrit (increased oxygen carrying-capacity of the blood). Unlike mammals, but similar to squamate reptiles, alligators do not also increase citrate synthase activity of the skeletal muscles in response to exercise.
authors.affiliation: Ecology and Evolutionary Biology, University of California, Irvine, 321 Steinhaus Hall, Irvine, CA 92697-2525, USA. jeme@uci.edu
authors.forename: John
authors.initials: J
authors.lastname: Eme
authors.forename: Tomasz
authors.initials: T
authors.lastname: Owerkowicz
authors.forename: June
authors.initials: J
authors.lastname: Gwalthney
authors.forename: Jason M
authors.initials: JM
authors.lastname: Blank
authors.forename: Bryan C
authors.initials: BC
authors.lastname: Rourke
authors.forename: James W
authors.initials: JW
authors.lastname: Hicks
mesh_terms: D000489:Alligators and Crocodiles / Q000502:physiology*; D000818:Animals; D002245:Carbon Dioxide / Q000378:metabolism; D002950:Citrate (si)-Synthase / Q000378:metabolism; D005080:Exercise Test / Q000662:veterinary; D005260:Female; D006321:Heart / Q000033:anatomy & histology; D006400:Hematocrit / Q000662:veterinary; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D018482:Muscle, Skeletal / Q000033:anatomy & histology / Q000201:enzymology; D009929:Organ Size; D010101:Oxygen Consumption; D010805:Physical Conditioning, Animal / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*; D012420:Running; D013045:Species Specificity; D013550:Swimming
chemical_list: D002245:Carbon Dioxide; D007770:L-Lactate Dehydrogenase; D002950:Citrate (si)-Synthase