Effects of growth hormone on thyroid function are mediated by type 2 iodothyronine deiodinase in humans

Purpose Growth hormone (GH) therapy in adults alters thyroid function, and acromegaly often involves thyroid disease. The present study aimed to elucidate roles and mechanisms of GH in regulating thyroid function. Methods We performed two retrospective observational studies, which focused on consecutive patients with severe adult GH deficiency who received recombinant human GH (rhGH) therapy ( n = 20) and consecutive patients with acromegaly who underwent transsphenoidal surgery (TSS) ( n = 25). In both studies, serum free triiodothyronine (fT3), free thyroxine (fT4), and fT3/fT4 ratio were examined before and after the interventions. We subsequently administered GH to four human cell lines (HepG2, TSA201, MCF7, and HTC/C3) in vitro, and examined changes in mRNA levels of iodothyronine deiodinases (D1, D2, and D3). Results Median serum fT3 level significantly increased after rhGH therapy from 2.38 to 2.78 pg/mL ( p