Meeting Abstract

48.3  Saturday, Jan. 5  Metabolic Substrate Utilization in Response to Temperature Acclimation and Insulin Exposure in Frog Skeletal Muscle PETERSEN, A.M.*; GLEESON, T.T.; University of Colorado, Boulder; University of Colorado, Boulder ann.petersen@colorado.edu

Animals alter metabolic fuel use in order to suit changes in energy requirements brought about by such challenges as prolonged activity, hibernation, or starvation. We test whether low temperature acclimation also alters oxidation and storage patterns of metabolic substrate in frogs. We employed radio-isotope tracer methods in order to test how skeletal muscle tissue in the American Bullfrog (Rana catesbeiana) responds to temperature acclimation and insulin exposure. Bullfrogs are an interesting species in which to investigate questions of temperature acclimation because they inhabit a wide geographic range and can be considered eurythermal, tolerating diurnal changes in pond temperature of up to 30 C. We measured the metabolic fate of physiologically relevant levels of exogenous glucose (1mM), lactate (5mM), and palmitate (1mM) in isolated Sartorius muscles at 5, 15, and 25 C both before and after frogs were acclimated to 5 or 25 C. We found that the Q10 of glucose oxidation was 3.0 between 5 and 25 C, but changes following six weeks of acclimation, more than doubling following acclimation to 5 C and reduced by two-thirds in response to 25 C acclimation. Substrate preference also appears to shift following acclimation. Exogenous glucose oxidation is increased, lactate oxidation remains constant, and free fatty acid oxidation is reduced following acclimation to low temperature. Interestingly, in all treatments lactate appears to be the primary oxidative substrate in frog muscle. We will discuss how insulin may alter these patterns. Furthermore, we will present data on the temperature dependence of insulin sensitivity in frog muscle and how insulin affects substrate utilization after different temperature acclimations.