Gluconeogenesis in frogs during cooling and dehydration exposure: new insights into tissue plasticity of the gluconeogenic pathway dependent on abiotic factors.

Anurans undergo significant physiological changes when exposed to environmental stressors such as low temperatures and humidity. Energy metabolism and substrate management play a crucial role in their survival success. Therefore, understanding the role of the gluconeogenic pathway and demonstrating its existence in amphibians is essential. In this study, we exposed the subtropical frog Boana pulchella to cooling (-2.5°C for 24 h) and dehydration conditions (40% of body water loss), followed by recovery (24 h), and assessed gluconeogenesis activity from alanine, lactate, glycerol and glutamine in the liver, muscle and kidney. We report for the first time that gluconeogenesis activity by 14C-alanine and 14C-lactate conversion to glucose occurs in the muscle tissue of frogs, and this tissue activity is influenced by environmental conditions. Against the control group, liver gluconeogenesis from 14C-lactate and 14C-glycerol was lower during cooling and recovery (P<0.01), and gluconeogenesis from 14C-glutamine in the kidneys was also lower during cooling (P<0.05). In dehydration exposure, gluconeogenesis from 14C-lactate in the liver was lower during recovery, and that from 14C-alanine in the muscle was lower during dehydration (P<0.05). Moreover, we observed that gluconeogenesis activity and substrate preference respond differently to cold and dehydration. These findings highlight tissue-specific plasticity dependent on the nature of the encountered stressor, offering valuable insights for future studies exploring this plasticity, elucidating the importance of the gluconeogenic pathway and characterizing it in anuran physiology.

Metabolic changes in the subtropical frog Boana pulchella during experimental cooling and recovery conditions.

Frogs have developed biochemical and physiological adaptations to occupy diverse ecological niches on Earth successfully. Survival in frozen states is a fascinating strategy made possible by evolving adaptations to produce cryoprotectant solutes. The hylid frog Boana pulchella thrives in South American regions with cold climates, remaining active while enduring sporadic subzero temperatures during winter. The species' metabolic changes during subzero exposure remain unclear. Therefore, we exposed B. pulchella to cooling and recovery, assessing plasma and tissue metabolite changes. Cooling significantly reduced urea concentrations in plasma (P = 0.033), muscle (P = 0.001), heart (P = 0.009), and brain (P = 0.041) compared to acclimation. Liver glucose oxidation and glycogen synthesis were lower in cooling and recovery than in acclimation (P < 0.0001 and P = 0.0117, respectively). Muscle glycogen synthesis was lower in recovery than acclimation (P = 0.0249). These results demonstrate B. pulchella's physiological strategies during subzero exposure, likely reflecting species-specific evolutionary adaptations for brief subzero exposures that enable winter survival in its natural habitat.

Acute effects of a single moderate-intensity exercise bout performed in fast or fed states on cell metabolism and signaling: Comparison between lean and obese rats.

AIMS: Although the benefits of exercise can be potentiated by fasting in healthy subjects, few studies evaluated the effects of this intervention on the metabolism of obese subjects. This study investigated the immediate effects of a single moderate-intensity exercise bout performed in fast or fed states on the metabolism of gastrocnemius and soleus of lean and obese rats. MAIN METHODS: Male rats received a high-fat diet (HFD) for twelve weeks to induce obesity or were fed standard diet (SD). After this period, the animals were subdivided in groups: fed and rest (FER), fed and exercise (30 min treadmill, FEE), 8 h fasted and rest (FAR) and fasted and exercise (FAE). Muscle samples were used to investigate the oxidative capacity and gene expression of AMPK, PGC1α, SIRT1, HSF1 and HSP70. KEY FINDINGS: In relation to lean animals, obese animals' gastrocnemius glycogen decreased 60 %, triglycerides increased 31 %; glucose and alanine oxidation decreased 26 % and 38 %, respectively; in soleus, triglycerides reduced 46 % and glucose oxidation decreased 37 %. Exercise and fasting induced different effects in glycolytic and oxidative muscles of obese rats. In soleus, fasting exercise spared glycogen and increased palmitate oxidation, while in gastrocnemius, glucose oxidation increased. In obese animals' gastrocnemius, AMPK expression decreased 29 % and SIRT1 increased 28 % in relation to lean. The AMPK response was more sensitive to exercise and fasting in lean than obese rats. SIGNIFICANCE: Exercise and fasting induced different effects on the metabolism of glycolytic and oxidative muscles of obese rats that can promote health benefits in these animals.

Seasonal variations in the intermediate metabolism in South American tree-frog Boana pulchella.

Seasonal metabolic changes can be observed in many anurans' species. In subtropical environments with environmental temperatures variations, the temperature is a factor that can influence the extent and intensity of activity in many anuran species. Nonetheless, some species of subtropical frogs may remain active throughout the year. Boana pulchella, a subtropical species, seems to be able to survive low temperatures and remain reproductively active even in the coldest months. Therefore, we hypothesized that B. pulchella presents seasonal changes in the energy metabolism to sustain activity during all year. This study evaluated the main energy substrate levels and metabolism of B. pulchella in plasma, liver and muscle of male individuals collected in winter, spring, summer and fall in the state of Rio Grande do Sul, Brazil. Our results showed that B. pulchella has a higher glycolytic oxidation rate in liver (P = 0.0152) and muscle (P = 0.0003) and higher glycogenesis from glucose in muscle (P = 0.0002) in summer, indicating the main energy substrates in this season is glucose. The higher muscle glycogen (P = 0.0008) and lower plasma glucose in fall (P = 0.0134) may indicate an anticipatory regulation for storing to the most thermally demanding cold period: winter. These results indicated seasonal differences in the main energy substrates, and these metabolic changes among seasons can be part of a metabolic adjustment allowing maintenance of reproductive activity all year in Boana pulchella species.

Metabolic and Molecular Subacute Effects of a Single Moderate-Intensity Exercise Bout, Performed in the Fasted State, in Obese Male Rats.

Introduction and objectives: Obesity represents a major global public health problem. Its etiology is multifactorial and includes poor dietary habits, such as hypercaloric and hyperlipidic diets (HFDs), physical inactivity, and genetic factors. Regular exercise is, per se, a tool for the treatment and prevention of obesity, and recent studies suggest that the beneficial effects of exercise can be potentiated by the fasting state, thus potentially promoting additional effects. Despite the significant number of studies showing results that corroborate such hypothesis, very few have evaluated the effects of fasted-state exercise in overweight/obese populations. Therefore, the aim of this study was to evaluate the subacute effects (12 h after conclusion) of a single moderate-intensity exercise bout, performed in either a fed or an 8 h fasted state, on serum profile, substrate-content and heat shock pathway-related muscle protein immunocontent in obese male rats. Methods: Male Wistar rats received a modified high-fat diet for 12 weeks to induce obesity and insulin resistance. The animals were allocated to four groups: fed rest (FER), fed exercise (FEE), fasted rest (FAR) and fasted exercise (FAE). The exercise protocol was a 30 min session on a treadmill, with an intensity of 60% of VO2max. The duration of the fasting period was 8 h prior to the exercise session. After a 12 h recovery, the animals were killed and metabolic parameters of blood, liver, heart, gastrocnemius and soleus muscles were evaluated, as well as SIRT1 and HSP70 immunocontent in the muscles. Results: HFD induced obesity and insulin resistance. Soleus glycogen concentration decreased in the fasted groups and hepatic glycogen decreased in the fed exercise group. The combination of exercise and fasting promoted a decreased concentration of serum total cholesterol and triglycerides. In the heart, combination fasting plus exercise was able to decrease triglycerides to control levels. In the soleus muscle, both fasting and fasting plus exercise were able to decrease triglyceride concentrations. In addition, heat shock protein 70 and sirtuin 1 immunocontent increased after exercise in the gastrocnemius and soleus muscles. Conclusions: An acute bout of moderate intensity aerobic exercise, when realized in fasting, may induce, in obese rats with metabolic dysfunctions, beneficial adaptations to their health, such as better biochemical and molecular adaptations that last for at least 12 h. Considering the fact that overweight/obese populations present an increased risk of cardiovascular events/diseases, significant reductions in such plasma markers of lipid metabolism are an important achievement for these populations.