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Serum insulin-like growth factor I increases in response to thyroxine in patients with hypothyroidism
The background of the study. Both thyroid hormone and growth hormone (GH) are needed for normal growth. The latter acts primarily by stimulating the production of insulin-like growth factor I (IGF-I). GH and therefore IGF-I production are decreased in patients with hypothyroidism and hypopituitarism. In this study, serum IGF-I was measured in patients with primary hypothyroidism and central hypothyroidism (hypopituitarism) before and during thyroxine (T4) therapy.
How the study was done. The study subjects were 18 patients with hypothyroidism caused by thyroid disease (primary hypothyroidism) and 10 with hypothyroidism caused by pituitary disease (central hypothyroidism); the latter patients also had GH deficiency. Serum IGF-I was measured at base line and later, when the patients were euthyroid during treatment with T4.
The results of the study. The average serum TSH and free T4 concentrations in the patients with primary hypothyroidism were very high and low, respectively, at base line and both were normal during T4 therapy. Their base-line serum IGF-I concentration was low (101 µg/L), and it increased to normal (158 µg/L) during T4 therapy.
The average serum free T4 concentration in the patients with central hypothyroidism was low at base line, and it increased during T4 therapy. Their base line serum IGF-I concentration was lower than in the patients with primary hypothyroidism (49 µg/L) and increased, but not to normal (97 µg/L), during T4 therapy.
The conclusions of the study. Serum concentrations of IGF-I are low in patients with hypothyroidism, and increase during T4 therapy in patients with primary hypothyroidism and those with central hypothyroidism (and GH deficiency).
The original article. Schmid C, Zwimpfer C, Brandle M, Krayenbuhl PA, Zapf J, Wiesli P. Effect of thyroxine replacement on serum IGF-I, IGFBP-3 and the acid-labile subunit in patients with hypothyroidism and hypopituitarism. Clin Endocrinol (Oxf) 2006;65:706-11.
Next Article: The effect of thyroxine is greater when taken at bedtime than in the morning in patients with hypothyroidism |
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| Thyroid Digest Index | | | March 2007 Thyroid Digest |
