Evidence of insulin-like growth factor binding protein-3 proteolysis during growth hormone stimulation testing

Objectives: The ternary complex is composed of insulin-like growth factor (IGF)-I, IGF binding protein (IGFBP)-3 and acid labile subunit (ALS). Growth hormone (GH) promotes IGFBP-3 proteolysis to release free IGF-I, ALS, and IGFBP-3 fragments. Our aim was to determine whether elevated GH levels during GH stimulation testing would trigger IGFBP-3 proteolysis. Design: This prospective study of 10 short prepubertal children (height standard deviation score -2.37 +/- 0.31) used arginine and GH releasing hormone stimulation to study dynamic changes in the ternary complex moieties. IGFBP-3 was measured in two assays: a radioimmunoassay (RIA) that detects both cleaved and intact IGFBP-3; and an immunochemiluminescence assay (ICMA) that detects only intact IGFBP-3. Results: IGFBP-3 measured by RIA increased by 19% (p<0.05), while IGFBP-3 measured by ICMA did not significantly increase (6.1%). Conclusion: The significant increase in IGFBP-3 measured by RIA, but not ICMA, provides evidence of IGFBP-3 proteolysis during acute GH stimulation.