Brain metabolism under different anesthetic conditions using hyperpolarized [1-¹³C]pyruvate and [2-¹³C]pyruvate

Carbon-13 NMR spectroscopy (¹³C MRS) offers the unique capability to measure brain metabolic rates in vivo. Hyperpolarized ¹³C reduces the time required to assess brain metabolism from hours to minutes when compared with conventional ¹³C MRS. This study investigates metabolism of hyperpolarized [1-¹³C]pyruvate and [2-¹³C]pyruvate in the rat brain in vivo under various anesthetics: pentobarbital, isoflurane, α-chloralose, and morphine. The apparent metabolic rate from pyruvate to lactate modeled using time courses obtained after injection of hyperpolarized [1-¹³C]pyruvate was significantly greater for isoflurane than for all other anesthetic conditions, and significantly greater for morphine than for α-chloralose. The apparent metabolic rate from pyruvate to bicarbonate was significantly greater for morphine than for all other anesthetic conditions, and significantly lower for pentobarbital than for α-chloralose. Results show that relative TCA cycle rates determined from hyperpolarized ¹³C data are consistent with rates previously measured using conventional ¹³C MRS under similar anesthetic conditions, and that using morphine for sedation greatly improves detection of downstream metabolic products compared with other anesthetics.