The effect of insulin-like growth factor (IGF) and of human serum on steps in proteoglycan synthesis

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Abstract
Embryonic chick pelvic cartilages were incubated in the presence of insulin-like growth factor (IGF) (1-100 .mu.U/ml), and normal human serum (5%), with radiolabeled precursors of proteoglycan (PG) synthesis: L-[3-3H]serine, D-[6-3H]glucosamine and [35S]Na2SO4. IGF alone (1-15 .mu.U/ml), stimulated in a dose-dependent manner D-[6-3H]glucosamine incorporation into tissue-bound and soluble isolated glycosaminoglycan chains, L-[3-3H]Ser incorporation into PG molecules was not stimulated by IGF (1-100 .mu.U/ml), despite the increase in the uptake of this precursor into intact cartilage. [35S]Na2SO4 incorporation was unaffected by IGF. Serum promoted the uptake of all 3 precursors into tissue-bound glycosaminoglycans. IGF could stimulate PG synthesis not only by elongating existing chondroitin sulfate chains but also by increased synthesis of other sugar chains, e.g., keratan sulfate and oligosaccharides.