Effect of hyperthyroidism on insulin-like growth factor-I (IGF-I) and IGF-binding proteins in adolescent children

A study was performed on adolescent hyperthyroid patients to determine the effects of hyperthyroidism on insulin-like growth factor (IGF)-I and its bi nding proteins. Serum concentrations of immunoreactive total and free IGF-I , and IGF binding protein (IGFBP)-2 and IGFBP-3 were determined before and after correction of hyperthyroidism in eight patients with Grave's disease and compared to control patients matched for age, sex and pubertal stage. T he concentration of serum total IGF-I was not significantly different in th e hyperthyroid state and euthyroid state, and did not differ significantly from euthyroid controls. IGFBP-2 levels were elevated three-fold in hyperth yroid patients at the time of diagnosis of hyperthyroidism compared to cont rol subjects, and fell significantly during treatment, There was also a sig nificant positive correlation between serum IGFBP-2 concentrations and thyr oxine (T-4) concentrations in all subjects. Serum IGFBP-3 concentrations we re also elevated in hyperthyroid subjects and normalized with correction of the hyperthyroidism. There was also a positive correlation between serum T -4 and IGFBP-3 concentrations in all subjects, Despite the hyperthyroid-ind uced elevations in IGFBP-2 and -3, no significant difference in the serum c oncentration of free IGF-I before or after correction of the hyperthyroid c ondition was observed, We conclude that hyperthyroidism does not cause alte rations in the serum concentrations of either free or total IGF-I, However, both serum IGFBP-2 and IGFBP-3 concentrations were elevated during hyperth yroidism and correlated with serum T-4 levels. These abnormalities reversed with normalization of thyroid function.