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This version published online on September 4, 2007
Journal of Clinical Endocrinology & Metabolism, doi:10.1210/jc.2007-0941
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Right arrow Thyroid

Submitted on April 26, 2007
Accepted on August 23, 2007

Growth Hormone Replacement Improves Thyroxine Biological Effects: Implications for Management of Central Hypothyroidism

Manoel RA Martins, Fabio C Doin, William R Komatsu, Turibio L Barros-Neto, Valdir A Moises, and Julio Abucham*

Divisions of Endocrinology, and Cardiology, and Centro de Medicina do Esporte, da Escola Paulista de Medicina-Universidade Federal de São Paulo

* To whom correspondence should be addressed. E-mail: julioabucham{at}uol.com.br.

Context: The biological significance of GH-induced changes in serum TH concentrations is unknown. It has been suggested that serum FT4 should be targeted at the high normal range during GH replacement.

Objective: To evaluate the effects of GH replacement on thyroxine biological effects.

Hypothesis: If GH modulates thyroxine biological effects, serum FT4 should be targeted accordingly.

Design/Setting: Observational (Study 1) and interventional (Studies 2–3)/Outpatient.

Patients: 32 GHD patients (13 off GH; 22 on L-thyroxine).

Interventions: Study 2: Levothyroxine to increase FT4 (>1.0ng/dL). Study 3: GH administration or withdrawal.

Main outcome measures: FT4, TT3, myocardial isovolumic contraction time (ICT) and resting energy expenditure (REE).

Results: Study 1: OFF GH and ON GH groups had similar FT4, but OFF GH showed lower TT3 (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 TT3 (r=-0.48, r=0.58, P<0.05). Off GH, ICT correlated only with FT4 (P<0.01).

Study 2: Off GH, levothyroxine intervention increased FT4 (P=0.005), TT3 (P=0.012), decreased ICT (P=0.006), increased REE (P=0.013); ICT and FT4 changes correlated (r=-0.72, P=0.06). On GH, levothyroxine increased FT4 (P=0.0002), TT3 (P=0.014), REE (P=0.10), decreased ICT (P=0.049); REE and TT3 changes correlated (r=0.60, P=0.05).

Study 3: GH decreased FT4, increased TT3, decreased ICT, increased REE (P<0.05). REE correlated (P<0.05) with IGF-I (r=0.57), TT3 (r=0.64). ICT correlated only with TT3 (r=-0.47).

Conclusions: GH replacement improves the biological effects of thyroxine. Serum FT4 should be targeted at the high normal range in GHD patients only off GH replacement.
Key words: Central hypothyroidism • isovolumic contraction time • resting energy expenditure • levothyroxine therapy • growth hormone therapy






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