Serum insulin-like growth factor type 1, insulin-like growth factor-binding protein-1, and insulin-like growth factor-binding protein-3 concentrations in patients with thyroid dysfunction

Thyroid hormones play a role in the regulation of insulin-like growth factor type 1 (IGF-1) and insulin-like growth factor-binding protein-3 (IGFBP-3) expression, and both IGF-1 and IGFBPs have been shown to be related to the function and growth of the thyroid. Our aim was to evaluate serum concentrations of IGF-1, IGFBP-1, and IGFBP-3 in patients with thyroid dysfunction before and after normalization of thyroid function. The study was performed in 86 patients with thyroid dysfunction (43 hyperthyroid and 43 hypothyroid. patients) and 17 euthyroid subjects. Serum growth hormone (GH), insulin, IGF-1, IGFBP-1, and IGFBP-3 were measured in all patients before and after normalizing serum thyroid hormone concentrations. Hyperthyroid patients showed IGF-1 (198.8 +/- 17.0 mug/L) and IGFBP-3 levels (4.2 +/- 0.2 mg/L) similar to those found in the control group (217.9 +/- 20.3 mug/L and 4.2 +/- 0.3 mg/L, respectively). After therapy these levels significantly decreased to 156.6 +/- 11.1 mug/L (p < 0.01) and 3.3 +/- 0.1 mg/L (p < 0.001), respectively. IGFBP-1 concentrations were clearly higher than those found in controls (22.7 +/- 2.6 vs. 5.7 +/- 1.5 mug/L, p < 0.001) and exhibited a significant reduction after therapy for thyroid hyperfunction (11.0 +/- 1.7 mug/L, p < 0.001). Patients with hypothyroidism showed serum concentrations of IGF-1 (161.5 +/- 13.1 mug/L, p < 0.05) and IGFBP-3 (3.2 +/- 0.3 mug/L, p < 0.05) significantly lower than those found in healthy volunteers. However, replacement therapy with levothyroxine did not induce any significant modification of these concentrations (152.6 +/- 10.6 mug/L and 3.2 +/- 0.2 mg/L, respectively). Similarly, patients with thyroid hypofunction exhibited raised levels of IGFBP-1 (15.5 +/- 0.9 mug/L, p < 0.05 vs. control group) that were significantly decreased after therapy (8.8 <plus/minus> 1.4 mug/L, p < 0.01). The results of the present study show that thyroid status affects GH/IGF axis. Hypothyroidism is associated with significant reductions of IGF-1 and IGFBP-3, and IGFBP-1 is elevated in both hypothyroidism and hyperthyroidism.