Fasting-Induced Changes in Thyroid Hormone Economy in Normal and Acromegalic Subjects

To study whether high growth hormone (GH) milieu may counteract fasting-induced changes in thyroid hormone economy, we measured basal and TRH-stimulated TSH concentrations as well as thyroxine (total, TT₄ and free, FT₄), total triiodothyronine (TT₃) and total reverse T₃ (T_rT₃) before and after a 6-day fast in 6 healthy men and in 8 patients with acromegaly. Baseline values for all parameters were similar in both groups. Fasting induced similar increases in TT₄ and TrT₃ concentrations and a similar decline in TT₃ concentrations in both groups. The TT₃/TT₄ and TrT₃/TT₄ ratios changed identically in both groups. We conclude that high GH is incapable of altering fasting-induced changes in thyroid hormone economy.