Meeting Abstract

90.9  Wednesday, Jan. 7  Effects of exercise on skeletal growth and bone microstructure of the American alligator with and without the cardiac shunt OWERKOWICZ, T.*; TSAI, H.P.; BLANK, J.M.; EME, J.; GWALTHNEY, J.W.; HICKS, J.W.; UC Irvine; UC Irvine; UC Irvine; UC Irvine; UC Irvine; UC Irvine towerkow@uci.edu

Exercise can affect the vertebrate skeleton via biomechanic or biochemical stress. Exercise-induced strains can elicit increased primary bone formation and/or secondary remodelling of limb bones. Strenuous exercise can result in high lactic acid loads, which may require buffering by bone mineral and perhaps influence bone remodelling. Cardiac shunting in crocodylians is thought to divert protons to the enteric circulation, and may thus reduce acidity of systemic arterial blood supplying bones of exercise-stressed animals. We subjected juvenile female American alligators (Alligator mississippiensis) to exhaustive exercise (running or swimming) every other day for 17 months, and compared their whole-body growth (mass, total and snout-to-vent lengths) and skeletal microstructure with those of sedentary controls. Prior to exercise training, half the animals in each group had their left aorta surgically occluded, thus rendering them incapable of cardiac shunting. Alligators were fed ad libitum twice weekly, and given injections of fluorescent dyes (calcein and alizarin) to determine bone deposition rate. Preliminary data (n=3 per group) show that bone formation rate at the femoral midshaft correlates with whole-body growth rate in all groups, but is significantly higher in treadmill runners. This suggests that terrestrial, but not aquatic, exercise stimulates periosteal bone formation. Neither exercise regime induced secondary remodelling in the femoral cortex. Loss of cardiac shunting did not reduce bone formation or accelerate resorption, which suggests cardiac shunting does not protect skeletal integrity in alligators. Funded by NSF IOB 04445680 to JWH. TO and JMB supported by NIH training grant 2T32AR047752 to V.J. Caiozzo.