Whole body and forearm substrate metabolism in hyperthyroidism: Evidence of increased basal muscle protein breakdown

Anne Lene Dalkjær Riis, Jens Otto Lunde Jørgensen, Signe Gjedde, Helene Nørrelund, Anne Grethe Jurik, K. S. Nair, Per Ivarsen, Jørgen Weeke, Niels Møller

Research output: Contribution to journalArticlepeer-review

40 Scopus citations


Thyroid hormones have significant metabolic effects, and muscle wasting and weakness are prominent clinical features of chronic hyperthyroidism. To assess the underlying mechanisms, we examined seven hyperthyroid women with Graves' disease before (Ht) and after (Eut) medical treatment and seven control subjects (Ctr). All subjects underwent a 3-h study in the postabsorptive state. After regional catheterization, protein dynamics of the whole body and of the forearm muscles were measured by amino acid tracer dilution technique using [ 15N]phenylalanine and [2H4]tyrosine. Before treatment, triiodothyronine was elevated (6.6 nmol/l) and whole body protein breakdown was icreased 40%. The net forearm release of phenylalanine was increased in hyperthyroidism (μg·100 ml-1·min -1): -7.0 ± 1.2 Ht vs. -3.8 ± 0.8 Eut (P = 0.04), -4.2 ± 0.3 Ctr (P = 0.048). Muscle protein breakdown, assessed by phenylalanine rate of appearance, was increased (μg·100 ml -1·min-1): 15.5 ± 2.0 Ht vs. 9.6 ± 1.4 Eut (P = 0.03), 9.9 ± 0.6 Ctr (P = 0.02). Muscle protein synthesis rate did not differ significantly. Muscle mass and muscle function were decreased 10-20% before treatment. All abnormalities were normalized after therapy. In conclusion, our results show that hyperthyroidism is associated with increased muscle amino acid release resulting from increased muscle protein breakdown. These abnormalities can explain the clinical manifestations of sarcopenia and myopathy.

Original languageEnglish (US)
Pages (from-to)E1067-E1073
JournalAmerican Journal of Physiology - Endocrinology and Metabolism
Issue number6 51-6
StatePublished - Jun 2005


  • Amino acids
  • Energy metabolism
  • Hyperthyroidism
  • Protein breakdown
  • Protein synthesis
  • Skeletal muscle
  • Stable isotopes
  • Tracers

ASJC Scopus subject areas

  • Endocrinology, Diabetes and Metabolism
  • Physiology
  • Physiology (medical)


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