Life without air: Metabolic responses of the tree frog Boana pulchella under anoxic conditions.

Amphibians possess intricate biochemical and physiological adaptations that enable survival in oxygen-deprived environments. Our study investigated metabolic and oxidative responses in the brain, skeletal muscle, liver, and plasma of the subtropical tree frog Boana pulchella exposed to 30 min of anoxia followed by normoxic recovery. Adult males were divided into control, anoxia, and recovery groups (n = 5 each). Key parameters measured included gluconeogenesis from lactate, catalase (CAT) and superoxide dismutase (SOD) activities, thiobarbituric acid reactive substances (TBARS), glucose oxidation, glycogen synthesis, and plasma and tissue metabolite levels. Plasma glucose, urea, and hemoglobin concentrations were stable, whereas plasma lactate increased significantly during anoxia (65% vs. control; 41% vs. recovery), confirming activation of anaerobic metabolism. In skeletal muscle, protein and urea concentrations were significantly higher in the recovery group compared to anoxia, indicating post-stress metabolic reactivation. In the liver, glucose oxidation increased by ∼66% and glycogen synthesis by ∼70% during anoxia, suggesting anticipatory energy storage, while brain gluconeogenesis from lactate declined nearly twofold, pointing to preferential lactate utilization as fuel. Antioxidant enzyme activities remained stable across tissues; however, hepatic TBARS increased ∼3.6-fold during anoxia compared to control, although this difference was not statistically significant, indicating a possible tendency toward oxidative imbalance. Principal component analyses revealed tissue-specific metabolic signatures: plasma responses driven by lactate and hemoglobin, liver by protein and TBARS, muscle by protein and urea, and brain by protein and urea. Together, these findings demonstrate that Boana pulchella maintains systemic stability under short-term anoxia through tissue-specific metabolic adjustments, with the liver acting as a central hub for energy regulation and the brain displaying metabolic flexibility to sustain function during oxygen deprivation.