title: Effects of levothyroxine on growth hormone (gh) sensitivity in children with idiopathic short stature.
abstract: BACKGROUND
  The possible relationship between the circulating concentrations of T4 and GH sensitivity has not been elucidated.
  
  
  OBJECTIVE
  The aim of this study is to evaluate the effect of levothyroxine supplementation on GH sensitivity in prepubertal boys with idiopathic short stature (ISS).
  
  
  METHODS
  We selected 28 prepubertal boys with ISS (mean age 8.2±0.5years) and free T4 (Ft4) concentrations between the 3rd and the 25th percentiles (Ft4: 0.8-1.5ng/dl). They were randomly divided into two groups: Group A received thyroid supplementation (1-3μg/kg/day) for 120days, and Group B received placebo for the same period. To evaluate GH sensitivity, an IGF-I generation test (GH: 33μg/kg/day sc for 3days) was performed in both groups: under basal conditions, and after 120days of levothyroxine supplementation (or placebo).
  
  
  RESULTS
  After thyroid supplementation, Group A had higher Ft4 concentrations compared with Group B (2.14±0.06 vs 1.48±0.06ng/dl, p=0.01), their growth velocity was significantly higher (2.3±0.1 vs 1.5±0.2cm/4months), and they exhibited a greater increase in IGF-I after GH administration (Group A: 32.5±3.8% vs Group B 17.3±2.6%).
  
  
  CONCLUSIONS
  Supplementation with levothyroxine for 120days promotes an increase in growth velocity, and a greater IGF-I response to short-term GH administration in prepubertal boys with ISS and low-normal thyroid hormone concentrations.
authors.affiliation: Institute of Maternal and Child Research (IDIMI), University of Chile, Santiago, Chile.
authors.forename: Roberto J
authors.initials: RJ
authors.lastname: García
authors.affiliation: Institute of Maternal and Child Research (IDIMI), University of Chile, Santiago, Chile.
authors.forename: German
authors.initials: G
authors.lastname: Iñiguez
authors.affiliation: San Borja Arriaran Hospital, Santiago, Chile.
authors.forename: Ximena
authors.initials: X
authors.lastname: Gaete
authors.affiliation: Institute of Maternal and Child Research (IDIMI), University of Chile, Santiago, Chile.
authors.forename: Jeannette
authors.initials: J
authors.lastname: Linares
authors.affiliation: Institute of Maternal and Child Research (IDIMI), University of Chile, Santiago, Chile.
authors.forename: Paula
authors.initials: P
authors.lastname: Ocaranza
authors.affiliation: San Borja Arriaran Hospital, Santiago, Chile.
authors.forename: Alejandra
authors.initials: A
authors.lastname: Avila
authors.affiliation: Institute of Maternal and Child Research (IDIMI), University of Chile, Santiago, Chile.
authors.forename: Rossana
authors.initials: R
authors.lastname: Roman
authors.affiliation: Institute of Maternal and Child Research (IDIMI), University of Chile, Santiago, Chile. Electronic address: fcassorl@med.uchile.cl.
authors.forename: Fernando
authors.initials: F
authors.lastname: Cassorla
mesh_terms: D001827:Body Height / Q000187:drug effects; D002648:Child; D006130:Growth Disorders / Q000188:drug therapy*; D013006:Growth Hormone / Q000627:therapeutic use*; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000032:analysis; D008297:Male; D013974:Thyroxine / Q000097:blood / Q000494:pharmacology / Q000627:therapeutic use*; D016896:Treatment Outcome
chemical_list: D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D013974:Thyroxine
keywords: Growth hormone; Growth hormone sensitivity; IGF-I; Idiopathic short stature; Levothyroxine