Correlation of sex steroids with IGF-1 and IGFBP-3 during different pubertal stages

Insulin-like growth factor 1 (IGF-1) is the major factor that affects linear bone growth. Also, androgens and estrogens are necessary for increasing longitudinal bone growth during sexual maturation. The aim of this study was to investigate the relationships among IGF-1 axis and sex steroids during pubertal development in healthy adolescents. In this cross-sectional study, IGF-1, IGF binding protein-3 (IGFBP-3) and sex steroid levels (estradiol in girls, testosterone in boys) of 205 healthy adolescents (101 female, 104 male) aged 9-17 years were measured. All subjects were apparently healthy, with no growth retardation and with skeletal ages appropriate for chronological ages, and none were taking medications known to influence calcium homeostasis. Greulich and Pyle's Radiographic Atlas of Skeletal Development of the Hand and Wrist was used for determination of skeletal ages. Tanner's classification was used to determine the pubertal developmental stage. Fasting blood samples were obtained from subjects between 09:00-10:00 h. Serum IGF-1 and IGFBP-3 levels differed significantly between pubertal developmental stages. Serum IGF-1 levels and IGF-1/IGFBP-3 ratios increased with proceeding stages and maximum mean values were found at stages III-IV in girls and at stage IV in boys. Estradiol levels of girls and testosterone levels of boys differed significantly between stages, and in both sexes, serum IGF-1 levels and IGF-1/IGFBP-3 ratios were significantly correlated with sex steroid levels. Increase in growth hormone secretion increases IGF-1 levels. Furthermore, increasing sex steroids with pubertal development increase the IGF-1 levels and IGF-1/IGFBP-3 ratios that affect bone growth.