CHARACTERIZATION OF INSULIN-LIKE GROWTH-FACTORS AND THEIR BINDING-PROTEINS IN PERITONEAL DIALYSATE

Serum insulin-like growth factors (IGFs), which circulate bound to spe cific IGF binding proteins (IGFBPs), must exit the intravascular space before acting on target tissues. Little is known about the nature of IGF/IGFBPs in extravascular fluids of patients with chronic renal fail ure (CRF). Peritoneal dialysate (PD) was studied since, after a short incubation, PD contains proteins which have entered an extravascular s pace; thus, IGF/IGFBP forms in PD are more likely than serum forms to interact with target tissues. IGF-I and IGF-II, and IGFBPs 1-4, were r eadily identified by specific immunoassays and/or (125)iodine-IGF liga nd blotting of simultaneously obtained PD and serum samples from seven CRF children; IGFBP-3 was a major IGFBP in PD as in serum. Where quan titated, IGF and IGFBP levels in PD were approximately 10% of serum co ncentrations. After separation of PD and serum by size-exclusion chrom atography, serum had more IGFBP-3 in 150-kilodalton (kDa) than 35-kDa fractions, while PD had far less IGFBP-3 in 150-kDa than 35-kDa fracti ons. Immunoblot studies revealed a major 29-kDa IGFBP-3 fragment, in a ddition to intact 41- and 38-kDa IGFBP-3 forms, in PD and CRF serum; t he 29-kDa form predominated in the 35-kDa PD fractions. These data sug gest that the 29-kDa fragment is the IGFBP-3 form most likely to modul ate IGF effects on target tissues of CRF individuals.