Briefly, we are asking the question; how much flexibility do physiological systems have to respond to different functional demands? How is priority accorded during conflicting simultaneous demand? These are extremely important because in nature organisms must undertake many different kinds of activities and sometimes do more than one thing at a time. Their physiological design must accommodate these demands, but the patterns of plasticity and prioritization that underlie this accommodation remain largely unexplored. In our study, we propose to investigate experimentally the response of a single physiological complex, the cardiopulmonary system, to increased functional demand in two different performance states: exercise and digestion. Large reptiles will be used as experimental study organisms. The physiological demands of exercise and digestion are similar in some ways and dissimilar in others. Both states require increased convection of air and blood to permit oxygen uptake, carbon dioxide release, and nutrient uptake and delivery; both may attain similarly high and limiting levels of exchange in our experimental animals. However, the physiology underlying these metabolic increments is very different in its tissue location (skeletal muscle vs. gastrointestinal tract), metabolic pattern (catabolism vs. anabolism), activating system (somatic motor and sympathetic nervous systems vs. parasympathetic nervous system), acid-base status (acidosis vs. alkalosis), and time course (minutes vs. hours or days). We will determine whether the cardiopulmonary response to equal metabolic demands during these different performance states is stereotyped or plastic. In the former case, equal metabolic increments (e.g., ml O2 or J) in either the skeletal muscle or the intestines would elicit an equal increment in cardiac response (heart rate and stroke volume, with appropriate redistribution of blood flow) and ventilatory response (breathing frequency and tidal volume) regardless of the performance state generating the demand. In the latter case, the cardiopulmonary system might have a variety of state-dependent and -appropriate responses that result in the same level of gas exchange. In such a plastic system, the convective components (either cardiac output or ventilation) might differ markedly, depending on the location and type of metabolic increment, appropriate to matching more subtle factors than simple energetic demand.

Hicks, J.W. and Wang, T. (1999) Hypoxic hypometabolism in the anesthetized turtle, Trachemys scripta. Amer. J. Physiol. Jul, 277(1 Pt 2):R18-23.

Owerkowicz, T., Farmer, C. , Hicks, J.W. and Branierd, B. (1999) Breathing under mechanical constraint: contribution of gular pumping to locomotor stamina in monitor lizards. Science. Jun 4, 284(5420):1661-3

Hicks, J.W. and Farmer, C.G. (1999) Gas exchange potential in reptilian lungs: implications for the dinosaur-avian connection. Respir. Physiol. 117: 73-83

Overgaard, J., Busk, M., Hicks, J.W., Jensen, F.B. and Wang, T. (1999) Acid-base status and arterial oxygen transport following feeding in the snake Python molorus. Comp. Biochem. Physiol. 124A: 361-367

Bennett, A.F., Hicks, J.W. and Cullum, A (2000) An experimental test of the thermoregulatory hypothesis for the evolution of endothermy. Evolution (in press)

Farmer, C. G. and Hicks, J.W. (2000) Circulatory impairment induced by exercise in the lizard Iguana iguana. J Exp Biol. 2000;203(Pt 17):2691-2697.

Wang, T. and Hicks, J.W. (2000) An Integrative model to predict maximum O2 uptake in animals with central vascular shunts. Zoology- Analysis of Complex systems (in press)

Busk, M., Overgaard, J., Hicks, J.W., Bennett, A.F. and Wang, T. (2000) Effects of feeding on arterial blood gases in the American alligator, Alligator mississippiensis. J. Exp. Biol., 2000 Oct;203 Pt 20:3117-24.

Secor SM, Hicks JW, Bennett AF.(2000) Ventilatory and cardiovascular responses of a python (Python molurus) to exercise and digestion.J Exp Biol. 2000 Aug;203 Pt 16:2447-54.

Hicks JW, Wang T, Bennett AF. (2000) Patterns of cardiovascular and ventilatory response to elevated metabolic states in the lizard Varanus exanthematicus.J Exp Biol. 2000 Aug;203 Pt 16:2437-45.

Kemper WF, Lindstedt SL, Hartzler LK, Hicks JW, Conley KE. (2001) Shaking up glycolysis: Sustained, high lactate flux during aerobic rattling. Proc Natl Acad Sci U S A. 2001 Jan 16;98(2):723-8. Epub 2000 Dec 19.

Bennett AF, Hicks JW. (2001) Postprandial exercise: prioritization or additivity of the metabolic responses? J Exp Biol. 2001 Jun;204(Pt 12):2127-32.

Hicks, JW and Wang, T. (2004) Hypometabolism in reptiles: behavioural and physiological mechanisms that reduce aerobic demands. Respir Physiol Neurobiol. 2004 Aug 12;141(3):261-71