The effect of somatomedin and cortisol on embryonic chick cartilage in vitro indicates that somatomedin stimulates 35SO4 uptake while cortisol decreases it with no effect on glycosaminoglycan turnover. Xylosyltransferase activity is increased in crude fractions of somatomedin-treated cartilage but decreased in cortisol-treated cartilage. By using a Smith-degraded proteoglycan as an exogenous acceptor, xylosyltransferase activities from both treatments were equivalent, suggesting that the enzyme was not rate limiting. The results of xylosyltransferase assays conducted by mixing enzyme and endogenous acceptor from control, cortisol-treated, and somatomedin-treated cartilage, suggest both effects to be at the level of the acceptor protein.Speculation
Glucocorticoids and somatomedin may influence growth in children by regulating the synthesis of the glycosaminoglycan acceptor protein. Present studies suggest that both these hormones alter the synthesis of this protein. Somatomedin increases glycosaminoglycan acceptor protein concentration while cortisol decreases glycosaminoglycan acceptor protein, suggesting that the synthesis of this protein may be an important control mechanism in glycosaminoglycan biosynthesis and subsequent growth. The assumption that the effect is a specific one and that the glucocorticoids and somatomedin act at the same site is speculative at the present time, but provides an attractive hypothesis.