Hyperpolarized C-13 MRI Reveals Large Changes in Pyruvate Metabolism During Digestion in Snakes

Purpose Hyperpolarized C-13 MRI is a powerful technique to study dynamic metabolic processes in vivo; but it has predominantly been used in mammals, mostly humans, pigs, and rodents. Methods In the present study, we use this technique to characterize the metabolic fate of hyperpolarized [1-C-13]pyruvate in Burmese pythons (Python bivittatus), a large species of constricting snake that exhibits a four- to tenfold rise in metabolism and large growth of the visceral organs within 24-48 h of ingestion of their large meals. Results We demonstrate a fivefold elevation of the whole-body lactate-to-pyruvate ratio in digesting snakes, pointing to a large rise in lactate production from pyruvate. Consistent with the well-known metabolic stimulation of digestion, measurements of mitochondrial respiration in hepatocytes in vitro indicate a marked postprandial upregulation of mitochondrial respiration. We observed that a low SNR of the hyperpolarized C-13 produced metabolites in the python, and this lack of signal was possibly due to the low metabolism of reptiles compared with mammals, preventing quantification of alanine and bicarbonate production with the experimental setup used in this study. Spatial quantification of the [1-C-13]lactate was only possible in postprandial snakes (with high metabolism), where a statistically significant difference between the heart and liver was observed. Conclusion We confirm the large postprandial rise in the wet mass of most visceral organs, except for the heart, and demonstrated that it is possible to image the [1-C-13]pyruvate uptake and intracellular conversion to [1-C-13]lactate in ectothermic animals.