caa a22 4500 465826520 CHVBK 20180323112151.0 cr unu---uuuuu 170327e19900801xx s 000 0 eng 10.1007/BF00302600 doi (NATIONALLICENCE)springer-10.1007/BF00302600 Lactate: a substrate for reptilian muscle gluconeogenesis following exhaustive exercise [Elektronische Daten] [Todd Gleeson, Paula Dalessio] Summary: The pattern of lactate and glycogen metabolism in red and white muscle fibers was examined in fasted, cannulated lizards (Dipsosaurus dorsalis) run on a treadmill to exhaustion. The white and red portions of the iliofibularis (wIF, rIF) muscle of the hindlimb were analyzed post-exercise and at intervals over 120 min of recovery for lactate and glycogen changes. Five min of exercise resulted in lactate concentrations of from 35 mM (rIF) to 48 mM (wIF) while blood lactate concentrations were elevated to 21 mM from resting levels of 1.8 mM. Glycogen depletion was significant (p<0.05) in whole hindlimb (−30%) and in wIF (−42%) but not in rIF (−25%). Metabolite changes were consistent with a pattern of fiber type recruitment favoring fast-twitch glycolytic (FG) fibers during high intensity locomotion. Glycogen replenishment during recovery was fiber typespecific. After 2 h recovery, whole hindlimb glycogen concentration had increased 24% above pre-exercise levels (p<0.05). Rates of glycogen resynthesis during recovery were significant only in oxidative fibers of the red iliofibularis. Animals were infused with either [U-14C]-lactate or [U-14C]-glucose at the point of exhaustion, and label incorporation into muscle glycogen was used to estimate the substrate preference for glycogenesis during recovery. Lactate uptake and incorporation occurred in both wIF and rIF. Glucose uptake and incorporation into glycogen was greatest in the rIF, where it equalled 9% of the rate of lactate incorporation. The rate of lactate incorporation could account for 67% of the rate of glycogen synthesis that occurred in oxidative fibers of the rIF. The data indicate that in contrast to mammalian muscle, reptilian muscle replenishes glycogen while it removes lactate, utilizing lactate directly as a gluconeogenic substrate. The data also suggest that lactate produced by FG fibers during exercise is utilized by oxidative fiber types post-exercise to synthesize glycogen in excess of pre-exercise levels. Springer-Verlag, 1990 Gluconeogenesis nationallicence Glycogenesis nationallicence Skeletal muscle nationallicence Fiber types nationallicence Lactate shuttle nationallicence Glycogen nationallicence wIF, rIF : white, red portions of iliofibularis muscle nationallicence FG : fast-twitch, glycolytic muscle fiber nationallicence FOG : fast-twitch, oxidative, glycolytic muscle fiber nationallicence HPLC : high performance liquid chromatography nationallicence SA : specific activity nationallicence [ LA ] : lactate concentration nationallicence GLU : glucose nationallicence ANOVA : analysis of variance nationallicence C.I. : confidence interval nationallicence Gleeson Todd Department of Environmental, Population and Organismic Biology, University of Colorado, 80309-0334, Boulder, CO, USA aut Dalessio Paula Department of Environmental, Population and Organismic Biology, University of Colorado, 80309-0334, Boulder, CO, USA aut Journal of Comparative Physiology B Springer-Verlag 160/3(1990-08-01), 331-338 0174-1578 160:3<331 1990 160 360 https://doi.org/10.1007/BF00302600 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/BF00302600 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Gleeson Todd Department of Environmental, Population and Organismic Biology, University of Colorado, 80309-0334, Boulder, CO, USA aut NATIONALLICENCE 700 1- Dalessio Paula Department of Environmental, Population and Organismic Biology, University of Colorado, 80309-0334, Boulder, CO, USA aut NATIONALLICENCE 773 0- Journal of Comparative Physiology B Springer-Verlag 160/3(1990-08-01), 331-338 0174-1578 160:3<331 1990 160 360 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer