Changes in Deiodinase Activity and Analysis of Related Influencing Factors in Growth Hormone-Secreting Pituitary Adenoma

Abstract Purpose Free triiodothyronine (FT3)/ free thyroxine (FT4) ratio is often considered as an indicator of deiodinase activity in the context of multiple diseases. We aimed to investigate the changes in deiodinase activity in growth hormone-secreting pituitary adenoma (GHPA) patients at high levels of growth hormone (GH) / insulin-like growth factor-1 (IGF-1) and analyze related influencing factors. Methods A retrospective cross-sectional study was conducted to collect demographic and clinical data of 128 GHPA patients with normal thyroid function from the Department of Endocrinology, Beijing Tiantan Hospital, Capital Medical University during 2015-2022. Pearson correlation test and linear regression analysis were used to analyze the relationship between FT3/ FT4 ratio and GH, IGF-1, insulin-like growth factor binding protein-3 (IGFBP-3), homeostasis model assessment of insulin resistance(HOMA-IR), body mass index (BMI) and age. Results 1. FT3/FT4 ratio was positively correlated with GH and IGFBP-3, but had no significant correlation with IGF-1. 2. FT3/FT4 ratio was positively correlated with BMI and negatively correlated with age. 3. FT3/FT4 ratio was positively correlated with fasting insulin (FINS) and HOMA-IR, but had no significant correlation with fasting C-peptide (FCP). 4. In multivariate analysis, FT3/FT4 ratio was independently associated with age and BMI. Conclusion In GHPA patients, high circulating levels of GH/IGF-1/IGFBP-3 system, high insulin level and elevated BMI may increase the activity of deiodinase, leading to increased peripheral T3 level, which may be a compensation mechanism of the body. Besides, deiodinase activity decreases with age, suggesting that elderly GHPA patients should be alerted to the risk of hypothyroidism.