IGF BINDING PROTEIN-3 IN PATIENTS WITH LARON TYPE DWARFISM - EFFECT OF EXOGENOUS RIGF-I

OBJECTIVE The aim of the study was to investigate the serum levels of IGFBP-3, the major IGF-I binding protein, in patients with Laron type dwarfism (LTD) before and after IGF-I treatment. DESIGN AND PATIENTS Eight Laron type dwarfism patients (four children and four adults) were treated for 7 days by one daily s.c. injection of biosynthetic IGF-I in doses of 120 or 150-mu-g/kg/day. MEASUREMENTS Blood was sampled in the fasting state before and 1 and 7 days after the last injection. RESULTS It was found that IGF-I administration significantly reduced plasma hGH levels with recovery after one week of no treatment. Serum IGFBP-3 was abnormally low (0.70 +/- 0.37 mg/l) and decreased significantly further during IGF-I treatment (to 0.48 +/- 0.28 mg/l) (P < 0.065). CONCLUSIONS The finding that serum IGFBP-3 is low in Laron type dwarfism, a disease due to molecular defects in the GH receptor, is compatible with the hypothesis that this IGF binding protein is GH-dependent. On the other hand the decrease during IGF-I administration and concomitant suppression of GH secretion may denote either that GH activity is not completely blocked in this syndrome or that there are additional mechanisms regulating IGFBP-3 synthesis.