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Nutrient Physiology, Metabolism, and Nutrient-Nutrient Interactions

Skeletal Muscle Protein Anabolic Response to Increased Energy and Insulin Is Preserved in Poorly Controlled Type 2 Diabetes^1,2

Jill A. Bell^*, Elena Volpi, Satoshi Fujita, Jerson G. Cadenas, Melinda Sheffield-Moore and Blake B. Rasmussen^*,**,3

Departments of ^* Kinesiology, Medicine, and ^** Biological Sciences, University of Southern California, Los Angeles, CA and Department of Internal Medicine, University of Texas Medical Branch, Galveston,TX

³ To whom correspondence should be addressed. E-mail: blrasmus{at}utmb.edu.

Type 2 diabetes (T2DM) subjects failing diet treatment are characterized by hyperinsulinemia and insulin resistance leading to fasting and postprandial hyperglycemia and hyperlipidemia. Energy is essential for allowing the process of protein synthesis to proceed. Additionally, insulin can stimulate protein synthesis in human muscle. The aims of this study were to determine if poorly controlled T2DM affects postabsorptive muscle protein anabolism, and if the muscle anabolic response to hyperinsulinemia with high energy availability is maintained. Control (n = 6) and T2DM subjects (n = 6) were studied in the postabsorptive state and during an isoenergetic high nutritional energy clamp (relative to postabsorptive state). Muscle protein synthesis and breakdown (nmol · min^–1 · 100 g leg muscle^–1) were assessed using stable isotope methodology, femoral arterio-venous sampling, muscle biopsies, and a three-pool model to calculate protein turnover. Postabsorptive phenylalanine net balance and whole body rate of appearance (Ra) were not different between groups; however, basal muscle protein breakdown was higher in T2DM (94 ± 9) than in controls (58 ± 12) (P < 0.05) and muscle protein synthesis tended (P = 0.07) to be elevated in T2DM (66 ± 14) compared with controls (39 ± 6). During the clamp, net balance increased, whole body Ra and muscle protein breakdown decreased (P < 0.05), and muscle protein synthesis tended to decrease (P = 0.08) to a similar extent in both groups. We conclude that postabsorptive muscle protein turnover is elevated in poorly controlled T2DM, however, there is no excessive loss of muscle protein because net balance is not different from controls. Moreover, the anabolic response to increased insulin and energy availability is maintained in T2DM.

KEY WORDS: • type 2 diabetes • protein metabolism • muscle protein synthesis • protein turnover

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