Evidence for Two Species of Insulin-Like Growth Factor Ii (Igf Ii and “Big” Igf Ii) in Human Spinal Fluid

Human serum contains the somatomedins, insulin-like growth factor I and II (IGF I and II). In spinal fluid, however, only IGF II was found in measurable and significant amounts. In addition, an IGF II of larger mass could be detected by a radioimmunoassay for IGF II. This "big" IGF II is biologically active and has an apparent molecular weight of 9000.