Growth hormone replacement improves thyroxine biological effects: Implications for management of central hypothyroidism
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2007-11-01
Autores
Martins, Manoel Ricardo Alves [UNIFESP]
Doin, Fabio Luiz Casanova [UNIFESP]
Komatsu, William Ricardo [UNIFESP]
Barros Neto, Turibio Leite de [UNIFESP]
Moisés, Valdir Ambrósio [UNIFESP]
Abucham, Julio [UNIFESP]
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Context: the biological significance of GH-induced changes in serum TH concentrations is unknown. It has been suggested that serum free T(4) (FT(4)) should be targeted at the high-normal range during GH replacement.Objective: Our objective was to evaluate the effects of GH replacement on T4 biological effects.Hypothesis: If GH modulates thyroxine biological effects, serum FT(4) should be targeted accordingly.Design and Setting: We conducted observational ( study 1) and interventional ( studies 2 and 3)/outpatient studies.Patients: Thirty-two GH-deficient patients ( 13 off GH; 22 on L-T(4)) participated in the study.Interventions: in study 2, levothyroxine was administered to increase FT(4) (> 1.0 ng/dl). in study 3, GH was administered or withdrawn.Main Outcome Measures: We measured FT(4), total T(3) (TT(3)), myocardial isovolumic contraction time (ICT), and resting energy expenditureResults: in study 1, off-GH and on-GH groups had similar FT(4), but off GH showed lower TT(3) ( P < 0.01) and REE ( P = 0.02), higher ICT ( P < 0.05) than on-GH and controls. On GH, ICT and REE correlated only with TT(3) ( r = -0.48; r = 0.58; P < 0.05). Off GH, ICT correlated only with FT(4) ( P = 0.01). in study 2, off GH, levothyroxine intervention increased FT(4) ( P = 0.005) and TT(3) ( P = 0.012), decreased ICT ( P = 0.006), and increased REE ( P = 0.013); ICT and FT(4) changes correlated ( r = -0.72; P = 0.06). On GH, levothyroxine increased FT(4) ( P = 0.0002), TT(3) ( P = 0.014), and REE ( P = 0.10) and decreased ICT ( P = 0.049); REE and TT(3) changes correlated ( r = 0.60; P = 0.05). in study 3, GH decreased FT(4), increased TT(3), decreased ICT, and increased REE ( P < 0.05). REE correlated ( P < 0.05) with IGF-I ( r = 0.57) and TT(3) ( r = 0.64). ICT correlated only with TT(3) ( r = -0.46).Conclusions: GH replacement improves the biological effects of T4. Serum FT(4) should be targeted at the high-normal range in GH-deficient patients only off GH replacement.
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Journal of Clinical Endocrinology & Metabolism. Chevy Chase: Endocrine Soc, v. 92, n. 11, p. 4144-4153, 2007.