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 (TrT3) 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.