The Fate of [U-13C]Palmitate Extracted by Skeletal Muscle in Subjects With Type 2 Diabetes and Control Subjects

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Abstract
The current study investigated the fate of a [U-13C]palmitate tracer extracted by forearm muscle in type 2 diabetic and control subjects. We studied seven healthy lean male subjects and seven obese male subjects with type 2 diabetes using the forearm muscle balance technique with continuous intravenous infusion of the stable isotope tracer [U-13C]palmitate under baseline conditions and during intravenous infusion of the nonselective β-agonist isoprenaline (ISO; 20 ng · kg−1 lean body mass · min−1). In skeletal muscle of control subjects, there was a significant release of 13C-labeled oxidation products in the form of 13CO2 (15% of 13C uptake from labeled palmitate) and a significant release of 13C-labeled glutamine (release of 13C-labeled atoms from glutamine was 6% of 13C uptake from labeled palmitate), whereas in type 2 diabetic subjects there was no detectable release of 13CO2 and 13C-glutamine, despite a significant uptake of [U-13C]palmitate (60% of control value). There was net uptake of arterial 13C-labeled glutamate by forearm muscle in both groups. Also, the ISO-induced increase in arterial glutamine enrichment and arterial concentration of 13C-glutamine was more pronounced in the diabetic group relative to control subjects. In view of the diminished ISO-induced release of 13C-glutamine from type 2 diabetic muscle, the latter data indicate that more [U-13C]palmitate entered the liver in the diabetic group and was incorporated into newly synthesized glutamine and glutamate molecules. Thus, the lack of release of 13C-labeled oxidation products by type 2 diabetic muscle during β-adrenergic stimulation, despite significant [U-13C]palmitate uptake, indicates differences in the handling of fatty acids between type 2 diabetic subjects and healthy control subjects.