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Thyroxine treatment increases circulating levels of insulin-like growth factor binding protein-1: a
M Angervo1, M Tiihonen, P Leinonen
1First Department of Obstetrics and Gynaecology, Helsinki University Central Hospital, Finland.
Objective:
Thyroid hormones affect carbohydrate metabolism in the liver, and hepatic insulin-like growth factor binding protein-1 (IGFBP-1) participates in glucose counter-regulation, so we studied the effects of oral thyroxine on serum IGFBP-1.
Design:
The study was performed on a placebo-controlled cross-over basis covering 3 months' thyroxine and 3 months' placebo administration.
Patients:
Eight patients taking anticonvulsant medication and four patients with hypothalamic hypothyroidism were given thyroxine, 150-200 micrograms daily for 3 months, or placebo.
Measurements:
Serum IGFBP-1, sex hormone binding globulin, free T3 and free T4, TSH and IGF-I levels were measured after an overnight fast before treatment, and at the end of each 3-month period.
Results:
Anticonvulsant medication had no significant effect on serum IGFBP-1. After 3 months' thyroxine treatment the serum IGFBP-1 levels (69; 58-167 micrograms/l; median and interquartile range, respectively) were significantly higher than those after placebo treatment (44; 23-58 micrograms/l; P = 0.002), or the pretreatment levels (54; 19-81 micrograms/l, P = 0.005). The IGFBP-1 levels rose in all 12 patients after thyroxine treatment, the median rise being 2.1-fold compared to placebo levels. No change was found in serum IGF-I concentrations.
Conclusions:
Oral thyroxine produces a rise in serum IGFBP-1 levels without a change in serum IGF-I concentration.