title: MECHANISMS IN ENDOCRINOLOGY: Exogenous insulin does not increase muscle protein synthesis rate when administered systemically: a systematic review.
abstract: BACKGROUND
  Though it is well appreciated that insulin plays an important role in the regulation of muscle protein metabolism, there is much discrepancy in the literature on the capacity of exogenous insulin administration to increase muscle protein synthesis rates in vivo in humans.
  
  
  OBJECTIVE
  To assess whether exogenous insulin administration increases muscle protein synthesis rates in young and older adults.
  
  
  METHODS
  A systematic review of clinical trials was performed and the presence or absence of an increase in muscle protein synthesis rate was reported for each individual study arm. In a stepwise manner, multiple models were constructed that excluded study arms based on the following conditions: model 1, concurrent hyperaminoacidemia; model 2, insulin-induced hypoaminoacidemia; model 3, supraphysiological insulin concentrations; and model 4, older, more insulin resistant, subjects.
  
  
  CONCLUSIONS
  From the presented data in the current systematic review, we conclude that: i) exogenous insulin and amino acid administration effectively increase muscle protein synthesis, but this effect is attributed to the hyperaminoacidemia; ii) exogenous insulin administered systemically induces hypoaminoacidemia which obviates any insulin-stimulatory effect on muscle protein synthesis; iii) exogenous insulin resulting in supraphysiological insulin levels exceeding 50, 000  pmol/l may effectively augment muscle protein synthesis; iv) exogenous insulin may have a diminished effect on muscle protein synthesis in older adults due to age-related anabolic resistance; and v) exogenous insulin administered systemically does not increase muscle protein synthesis in healthy, young adults.
authors: Department of Human Movement SciencesFaculty of Health, Medicine and Life Sciences, NUTRIM School for Nutrition, Toxicology and Metabolism, Maastricht University, PO Box 616, 6200 MD Maastricht, The NetherlandsDivision of Human NutritionWageningen University, Wageningen, The Netherlands.
authors: Jorn
authors: J
authors: Trommelen
authors: Department of Human Movement SciencesFaculty of Health, Medicine and Life Sciences, NUTRIM School for Nutrition, Toxicology and Metabolism, Maastricht University, PO Box 616, 6200 MD Maastricht, The NetherlandsDivision of Human NutritionWageningen University, Wageningen, The Netherlands.
authors: Bart B L
authors: BB
authors: Groen
authors: Department of Human Movement SciencesFaculty of Health, Medicine and Life Sciences, NUTRIM School for Nutrition, Toxicology and Metabolism, Maastricht University, PO Box 616, 6200 MD Maastricht, The NetherlandsDivision of Human NutritionWageningen University, Wageningen, The Netherlands.
authors: Henrike M
authors: HM
authors: Hamer
authors: Department of Human Movement SciencesFaculty of Health, Medicine and Life Sciences, NUTRIM School for Nutrition, Toxicology and Metabolism, Maastricht University, PO Box 616, 6200 MD Maastricht, The NetherlandsDivision of Human NutritionWageningen University, Wageningen, The Netherlands.
authors: Lisette C P G M
authors: LC
authors: de Groot
authors: Department of Human Movement SciencesFaculty of Health, Medicine and Life Sciences, NUTRIM School for Nutrition, Toxicology and Metabolism, Maastricht University, PO Box 616, 6200 MD Maastricht, The NetherlandsDivision of Human NutritionWageningen University, Wageningen, The Netherlands l.vanloon@maastrichtuniversity.nl.
authors: Luc J C
authors: LJ
authors: van Loon
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D003920:Diabetes Mellitus / Q000188:drug therapy; D005260:Female; D006801:Humans; D007004:Hypoglycemic Agents / Q000008:administration & dosage* / Q000494:pharmacology*; D007328:Insulin / Q000008:administration & dosage* / Q000494:pharmacology*; D008297:Male; D008875:Middle Aged; D009124:Muscle Proteins / Q000096:biosynthesis*; D009132:Muscles / Q000187:drug effects / Q000378:metabolism; D055815:Young Adult
chemical_list: D007004:Hypoglycemic Agents; D007328:Insulin; D009124:Muscle Proteins