Metabolic plasticity in the American bullfrog (Lithobates catesbeiana) [electronic resource]
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Online Access |
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| Format: | Thesis Electronic eBook |
| Language: | English |
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2008.
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| Abstract: | Anaerobic metabolism is thought to fuel most activity in frogs, suggesting a reliance on the glycolytic substrates, lactate and glucose. Northern amphibians must breed, feed, and escape predators under a wide variety of environmental conditions throughout the year. Yet it is not known how environmental factors such as temperature affect the metabolic fate of these two substrates. The goal of these experiments was to gain insight into how ectotherms fuel metabolism during changing seasonal conditions. This series of studies examined metabolism of lactate and glucose in response to (1) forced 2-minute activity (2) changes in season and (3) temperature, and (4) insulin exposure. The metabolic fate of 14C-labeled lactate and glucose in the American bullfrog, (Lithobates catesbeiana), was determined in vivo and in vitro in response to these conditions. It was found that during recovery from activity, approximately 85% of circulating lactate was taken up by muscle, identifying skeletal muscle as the major sink for post-activity extracellular lactate. Patterns of lactate metabolism were found to be stable between seasons. Hepatic and muscular glucose concentrations, however, changed significantly between winter and summer. Temperature exposure resulted in myriad alterations in pathways of substrate use. Long-term cold temperature acclimation resulted in high reliance by the muscle on lactate for substrate, as net rates of lactate oxidation and glyconeogenesis were orders of magnitude higher than those of glucose after acclimation under this condition. When muscles from cold or warm-acclimated frogs were incubated at a common temperature (15°C), glycogen incorporation from lactate and glucose were significantly higher in muscles from cold-acclimated frogs, indicative of positive thermal metabolic compensation. Insulin treatment resulted in increased glycogenesis, and increased intracellular [glucose], but inhibited lactate glyconeogenesis. Interestingly, temperature condition altered or even reversed insulin's effects on glucose metabolism. These studies demonstrate that patterns of glucose metabolism are particularly plastic, and are influenced by season, temperature, and insulin exposure. Pathways of lactate metabolism appear to be more stable, suggesting that this substrate may be a more reliable fuel source for the whole body during fluctuating environmental conditions in northern amphibians. |
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| Item Description: | Source: Dissertation Abstracts International, Volume: 69-04, Section: B, page: 2029. Adviser: Todd T. Gleeson. |
| Physical Description: | 172 pages. |
| ISBN: | 9780549508397 |