title: Growth hormone/insulin-like growth factor axis in patients with subclinical thyroid dysfunction.
abstract: OBJECTIVE
  Our aim was to evaluate serum concentrations of GH, IGF-I, and insulin-like growth factor-binding protein-3 (IGFBP-3) in patients with subclinical thyroid dysfunction before and after normalization of thyroid function.
  
  
  METHODS
  The study included 51 patients (mean age 42.2+/-1.8 years) with subclinical hypothyroidism and 30 patients (mean age 44.3+/-2.4 years) with subclinical hyperthyroidism. A group of 37 euthyroid healthy subjects were studied as controls. Serum concentrations of TSH, FT4, FT3, GH, insulin, IGF-I, and IGFBP-3 were measured in all patients before starting therapy and after normalization of thyroid function. The dosage of levothyroxine (LT4) and antithyroid drugs was adjusted in attempt to keep the serum-free thyroxine (FT4) and thyrotropin (TSH) concentrations within the normal range.
  
  
  RESULTS
  Baseline growth hormone levels were similar with hypothyroid group and hyperthyroid group in relation to euthyroid control subjects. Fasting serum IGF-I levels were significantly lower in the subclinical hypothyroid group compared with the control group. On the other hand, IGF-I levels of subclinical hyperthyroid patients and control group were similar. After normalization of thyroid function tests, IGF-I concentrations were increased in subclinical hypothyroid subjects, but unchanged in subclinical hyperthyroid subjects. Patients with subclinical hyperthyroidism showed slightly lower mean serum IGFBP-3 concentrations than those found in control group, but the difference was not statistically significant. Serum GH and IGFBP-3 levels were unaltered by treatment.
  
  
  CONCLUSIONS
  In this study, it was shown that GH-IGF axis was not affected in patients with subclinical hyperthyroidism, while it was affected in patients with subclinical hypothyroidism. That is, investigation of the axis in subclinical hyperthyroidism would not bring any extra advantages, but LT4 replacement therapy could prevent abnormalities related to GH-IGF axis in patients with subclinical hypothyroidism.
authors.affiliation: University of Pamukkale, Faculty of Medicine, Department of Endocrinology and Metabolism, Denizli, Turkey. fulyaendo@yahoo.com.tr
authors.forename: Fulya
authors.initials: F
authors.lastname: Akin
authors.forename: Guzin Fidan
authors.initials: GF
authors.lastname: Yaylali
authors.forename: Sebahat
authors.initials: S
authors.lastname: Turgut
authors.forename: Bunyamin
authors.initials: B
authors.lastname: Kaptanoglu
mesh_terms: D000328:Adult; D015415:Biomarkers / Q000097:blood*; D005260:Female; D019382:Human Growth Hormone / Q000097:blood*; D006801:Humans; D006980:Hyperthyroidism / Q000097:blood*; D007037:Hypothyroidism / Q000097:blood*; D007328:Insulin / Q000097:blood; D018972:Insulin-Like Growth Factor Binding Protein 3; D018969:Insulin-Like Growth Factor Binding Proteins / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D008297:Male; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood
chemical_list: D015415:Biomarkers; C515497:IGFBP3 protein, human; D007328:Insulin; D018972:Insulin-Like Growth Factor Binding Protein 3; D018969:Insulin-Like Growth Factor Binding Proteins; D019382:Human Growth Hormone; D007334:Insulin-Like Growth Factor I; D013972:Thyrotropin; D013974:Thyroxine