THYROXINE TREATMENT INCREASES CIRCULATING LEVELS OF INSULIN-LIKE GROWTH-FACTOR BINDING PROTEIN-1 - A PLACEBO-CONTROLLED STUDY

OBJECTIVE Thyroid hormones affect carbohydrate metabolism in the liver , and hepatic insulin-like growth factor binding protein-1 (IGFBP-1) p articipates in glucose counter-regulation, so we studied the effects o f 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 antic onvulsant medication and four patients with hypothalamic hypothyroidis m were given thyroxine, 150-200 mug daily for 3 months, or placebo. ME ASUREMENTS Serum IGFBP-1, sex hormone binding globulin, free T3 and fr ee T4, TSH and IGF-I levels were measured after an overnight fast befo re treatment, and at the end of each 3-month period. RESULTS Anticonvu lsant medication had no significant effect on serum IGFBP-1. After 3 m onths' thyroxine treatment the serum IGFBP-1 levels (69; 58-167 mug/l; median and interquartile range, respectively) were significantly high er than those after placebo treatment (44; 23-58 mug/l; P = 0.002), or the pretreatment levels (54; 19-81 mug/l, P = 0.005). The IGFBP-1 lev els rose in all 12 patients after thyroxine treatment, the median rise being 2.1-fold compared to placebo levels. No change was found in ser um IGF-I concentrations. CONCLUSIONS Oral thyroxine produces a rise in serum IGFBP-1 level without a change in serum IGF-I concentration.