Energy homeostasis in response to seasonal challenges in hibernating tegu lizards

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Over the last decade, many studies have uncovered complex mechanisms to cope with the environmental changes in small endothermic mammals that go into hibernation during the winter. In these animals, metabolic depression and low body temperatures during prolonged bouts of torpor minimize energy expenditure. However, the torpor is periodically interrupted by rewarming and brief periods with high energy turnover, and the large variations in body temperature represent a confounding factor in the interpretation of mechanisms of energy balance due to temperature dependence of many physiological processes. On the other hand, there are animals from tropical/subtropical regions that hibernate under gradual and mild changes in body temperatures. The tegu lizards (Salvator merianae) become dormant when average temperatures inside the hibernaculum diminish from 21-26°C to 15-20°C, and attain a degree of metabolic depression comparable to that of mammals that go into deep torpor when body temperatures around 37°C drop to near 0°C. Moreover, hibernation in tegu lizards is a continuous torpid state for most of the time, and therefore, they are valuable organisms to investigate seasonal effects on energy balance with minimal interference from temperature fluctuations. These features led us to investigate the antioxidant defenses that result in an adaptive stress response in the tegu. Large fluctuations in oxygen consumption are usually associated with altered mitochondrial reactive oxygen species production, which may cause oxidative stress, functional losses and death in animals. The adjustments of the antioxidant system in hibernating animals are poorly understood, particularly during the transition to hibernation. Thus, we focused on changes in the antioxidant system and in oxidative stress markers during the autumn period and in subsequent steps of the annual cycle in juvenile tegus. The propensity to accumulate oxidized molecules and the antioxidant response were examined across different organs systems, and will be discussed in light of physiological shifts in the annual cycle.

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