C-13 nuclear magnetic resonance study of glycogen resynthesis in muscle after glycogen-depleting exercise in healthy men receiving an infusion of lipid emulsion

In healthy individuals, glycogen recovery after a strong depletion is known to be rapid and insulin independent during the initial phase, and subseque ntly, slow and insulin dependent. Free fatty acids (FFAs) as a putative sou rce of insulin resistance (IR) could thus impair glycogen recovery during t he second period. Using in vivo C-13 nuclear magnetic resonance (NMR), we s tudied the effect of long-chain triglyceride emulsion on gastrocnemius glyc ogen resynthesis during a 3-h recovery period after 90 min of moderate exer cise consisting of plantar flexion on overnight-fasted healthy men (n = 8). In separate experiments, each subject was infused with 10% Ivelip (0.015 m l.kg(-1).min(-1)) or 10% glycerol (0.13 mg.kg(-1).min(-1)). NMR spectra wer e acquired before and at the end of the exercise and during the recovery pe riod. Whole-body glucose and lipid oxidation rates (indirect calorimetry), plasma insulin, C-peptide, glucose, lactate, beta-hydroxybutyrate, triglyce rides, and FFAs were determined. Glycogen consumption was 47.6 +/- 4.5% (gl ycerol) and 49.7 +/- 4.8% (Ivelip) of the initial glycogen. An acquired IR in the Ivelip group was significant at the onset of the recovery period by homeostasis model assessment (P = 0.002). Glycogen resynthesis in the glyce rol group appeared faster during the Ist h than during the subsequent 2nd h of the postexercise period. The glycogen resynthesis level was significant ly lower in the Ivelip group than in the glycerol group during the recovery period (P = 0.04 during the Ist h and P = 0.001 during the next 2 h). Duri ng the recovery, plasma lactate and whole-body oxidation rates were similar in the two groups, whereas glycemia was significantly higher in the Ivelip group. A decreased cellular uptake of glucose as a substrate for glycogeno synthesis, rather than a competition between oxidation of carbohydrate and FFA, is discussed.