title: Growth hormone potentiates thyroid hormone effects on post-exercise phosphocreatine recovery in skeletal muscle.
abstract: OBJECTIVE
  The aim of the study was to determine the respective impact of thyroxine and growth hormone on in vivo skeletal mitochondrial function assessed via post exercise phosphocreatine recovery.
  
  
  METHODS
  The hind leg muscles of 32 hypophysectomized rats were investigated using (31)P nuclear magnetic resonance spectroscopy at rest and during the recovery period following a non tetanic stimulation of the sciatic nerve. Each rat was supplemented with hydrocortisone and was randomly assigned to one of the 4 groups: the group Hx was maintained in hypopituitarism., the group HxT was treated with 1 μg/100g/day of thyroxine (T4), the group HxG with 0.2 IU/kg/day of recombinant human GH (rGH) and the group HxGT by both thyroxine and rGH. Inorganic phosphate (Pi), phosphocreatine (PCr) and ATP were directly measured on the spectra, permitting the calculation of the phosphorylation potential (PP).
  
  
  RESULTS
  At rest, the rats treated with rGH or T4 exhibited higher PCr levels than rats Hx. The recovery rates of PCr and PP were higher in rats treated with T4 than in T4-deprivated rats, suggesting improved mitochondrial function. The rats treated by both T4 and rGH showed higher PCr and PP recovery than those maintained in hypopituitarism or treated with T4 or rGH alone.
  
  
  CONCLUSIONS
  The study demonstrates that in contrast to T4, GH given alone in hypophysectomized rats does not improve in vivo mitochondrial oxidative metabolism. Growth hormone potentiates T4 effects on oxidative metabolism.
authors.affiliation: Pôle des Spécialités Médicales, Service de Médecine Interne, Centre Hospitalier Universitaire de Nancy, Hôpitaux de Brabois, 54500 Vandoeuvre, France. p.kaminsky@chu-nancy.fr
authors.forename: P
authors.initials: P
authors.lastname: Kaminsky
authors.forename: P M
authors.initials: PM
authors.lastname: Walker
authors.forename: J
authors.initials: J
authors.lastname: Deibener
authors.forename: F
authors.initials: F
authors.lastname: Barbe
authors.forename: E
authors.initials: E
authors.lastname: Jeannesson
authors.forename: J M
authors.initials: JM
authors.lastname: Escanye
authors.forename: B
authors.initials: B
authors.lastname: Dousset
authors.forename: M
authors.initials: M
authors.lastname: Klein
mesh_terms: D000818:Animals; D004357:Drug Synergism; D019382:Human Growth Hormone / Q000378:metabolism / Q000494:pharmacology*; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000378:metabolism; D010725:Phosphocreatine / Q000378:metabolism*; D010805:Physical Conditioning, Animal / Q000502:physiology*; D011897:Random Allocation; D051381:Rats; D013961:Thyroid Gland / Q000378:metabolism; D013974:Thyroxine / Q000494:pharmacology*
chemical_list: D010725:Phosphocreatine; D019382:Human Growth Hormone; D013974:Thyroxine