Effect of Human Growth Hormone on Thyroidal Secretion, Radiothyroxine Turnover and Transport in Man

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Abstract
Human growth hormone (HGH, Raben) was administered up to 15 days in biologically effective dosage (4–8 mg/day) to 8 normal adult volunteers to investigate its effect on various thyroid indices. The thyroidal secretion rate was measured in 2 subjects; radiothyroxine turnover, thyroxine binding to serum protein carriers and serum free thyroxine levels were studied in the remaining subjects. No effects were noted on thyroidal secretion, daily thyroxine degradation rate or the serum free thyroxine levels (% or concentration) as a result of HGH administration. However, HGH resulted in slight but significant decreases in concentrations of serum proteins, PBI and the binding capacity of thyroxine-binding globulin (TBG), the trend being noted as early as 5 days after HGH. Based on the data presented it was concluded that short-term HGH administration has no physiologically significant effect on thyroxine homeostasis in man, since the slight changes in serum proteins, PBI and TBG binding capacity were associated with unaltered radiothyroxine turnover and free thyroxine levels.