Suppression of sex steroids by a gonadotrophin-releasing hormone agonist increases serum growth hormone-binding protein activity in girls with central idiopathic precocious puberty.
OBJECTIVE: The high-affinity growth hormone (GH)-binding protein corresponds to the extracellular domain of GH receptor. The direct role of sex steroids in pubertal bone growth may be an increased GH receptor-coupled GH action. We examine the GH-binding protein (GHBP) activity before and after the suppression of female sex steroids and the relation of GHBP to pubertal growth. PATIENTS: We studied six girls with central idiopathic sexual precocity without any prior gonadal suppression therapy. DESIGN: We measured GHBP activity before and 12, 24 and 48 weeks after the treatment with s.c. injection of a GnRH agonist (leuprolide acetate) every 4 weeks. MEASUREMENT: GHBP activity was measured by immunoprecipitation using anti-GH receptor monoclonal antibody. RESULTS: The treatment caused a decrease in the LH and FSH responses to GnRH test and plasma oestradiol, which resulted in decreased urinary GH excretion, plasma IGF-I levels, height velocity and bone age maturation. GHBP activity before the start of the treatment was normal (75 +/- 27% relative to adult pooled serum, mean +/- SD), and it was increased above adult level (122 +/- 29% at 48 weeks, P < 0.01) by the suppression of the pituitary-gonadal axis. There were significant negative correlations between GHBP and oestradiol (r = 0.452, n = 24, P < 0.05) and between GHBP and urine GH excretion (r = -0.462, n = 24, P < 0.05). CONCLUSIONS: The high-affinity GHBP is increased by the withdrawal of female sex steroid. The clinical significance of this finding may be interference with the binding of GH to its receptor resulting in a reduced IGF-I level and decreased height velocity. The mechanism warrants further study.