Abstract
Insulin-like growth factor (IGF) is one of the important factors in the regulation of pubertal growth. Serum levels of IGF binding protein-3 (IGFBP-3), a major binding protein of IGF-I, and the proteolysis of IGFBP-3 modulate bioactivity of IGF-I. To investigate the effect of growth hormone (GH) on pubertal growth, IGF and IGFBP-3, immature female rats were hypophysectomized and GH was administered. Methods: Thirteen immature female rats (Wistar) at 28 days were hypophysectomized (Hx) . Recombinant hGH (0.4U/100g body weight) was administered daily for 2 weeks (Hx+GH group; n=5) . As contrasts, a sham operation was performed on 8 rats. Body weight was measured weekly and at 49 days, rats were sacrificed and blood samples were collected. Tibia length was measured. Serum IGF-I concentrations were measured by the RIA method and relative intensities of intact- and proteolysed IGFBP-3 expressions were measured by Western immunoblot (WIB) . Results: Body weight, tibia length and serum IGF-I levels were significantly decreased (p<0.05) by Hx. Administration of GH fully restored tibia length and IGF-I levels, while the body weight was not completely restored with the dose used. Relative intensity of intact IGFBP-3 in the Hx group was decreased significantly with augmentation of proteolysed IGFBP-3. In contrast, GH administration to Hx rats significantly increased intact IGFBP-3, and decreased proteolysed IGFBP-3. Conclusions: In the present study, the restoration of body growth, tibia length and serum IGF-I levels by GH administered to hypophysectomized immature female rats was demonstrated. Analysis of IGF-I, IGFBP-3, and proteolysed IGFBP-3 indicated that proteolysis of IGFBP-3, a potent modulator of IGF-I action, might be regulated by GH-IGF-I axis and plays an important role in pubertal development.
