Triiodothyronine Regulates Insulin‐Like Growth Factor‐I Binding to Cultured Rat Pituitary Cells

E. Stewart Geary, Matthew Lim, Gian Paolo Ceda, Sandy Ro, Ron G. Rosenfeld, Andrew R. Hoffman

Research output: Contribution to journalArticlepeer-review

16 Scopus citations


Triiodothyronine (T3) stimulates the synthesis of growth hormone and enhances the growth of neoplastic rat pituitary somatomam‐motrophs (GH cells) in culture. Moreover, T3 has been shown to stimulate the production and secretion of an autocrine growth factor by these cells. We have previously demonstrated the presence of specific receptors for insulin‐like growth factors (IGF) on GH cells. Since GH3 cells contain mRNA encoding IGF‐I, it has been suggested that IGF‐I might act in an autocrine fashion in these cells. Therefore, it was of interest to learn how T3 affects IGF‐I binding to GH3 cells. T3 increased [125I]IGF‐I binding in a time ‐ and dose‐dependent manner. After 48 h of exposure to T3, an increase in IGF‐I binding was seen with 10−11M T3, maximizing with 10−8M T3. When cells were exposed to 10−8 T3, [125I]IGF‐I binding reached a maximum of 218 ± 20.8% of control (±SEM, P < 0.002) after 72 h of incubation. Scatchard analysis indicated that T3 did not alter the Kd of IGF‐I for its receptor, but that the total receptor number was increased. Dexamethasone (10−7M) inhibited the T3‐induced increase in IGF‐I binding, but glucocorticoid alone did not substantially alter receptor number. No significant change in insulin or IGF‐II binding was seen after hormone treatment. 10−8 M T3 or IGF‐I increased the growth of the GH3 cells by ≥30%. Our data indicate that T3 upregulates IGF‐I binding in GH3 cells without altering insulin binding and thereby provides a means for enhancing potential autocrine regulation in this cell line.

Original languageEnglish (US)
Pages (from-to)179-184
Number of pages6
JournalJournal of Neuroendocrinology
Issue number3
StatePublished - Jun 1989
Externally publishedYes


  • autocrine
  • growth hormone
  • insulin‐like growth factor‐I
  • insulin‐like growth factor‐II
  • triiodothyronine

ASJC Scopus subject areas

  • Endocrinology, Diabetes and Metabolism
  • Endocrinology
  • Endocrine and Autonomic Systems
  • Cellular and Molecular Neuroscience


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