Serum somatomedin activity assayed by the enhancement of proteoglycan sulphation using chick embryo chondrocytes in normal children at various ages and children of short stature.

It was possible to obtain a sufficient amount of homogeneous chondrocytes from 13-day old chick embryo-sterna in an 8-day suspension culture. Serum somatomedin (SM) activity was measured on the basis of ability of serum to stimulate labelled sulphate uptake in these chondrocytes. Somatomedin A and multiplication stimulating activity (MSA) stimulated the sulphation in this assay. Serum SM activity in term cord sera and newborn sera was lower than that in normal adults. Serum SM activity in early infants increased rapidly and attained the levels of that in normal adults within 1 month following birth. Serum SM activity in infants (1 month - 2 years) and pubertal children (10-16 years), when the annual height increment is greatest, was higher than in normal adults. Serum SM activity in children with constituted dwarfism aged 6-10 years and over 10 years was normal and lower, respectively, compared to that in age-matched controls. Pituitary dwarfs had markedly low SM activity compared to age-matched controls. Diagnostic evaluation of serum SM activity in children requires comparison with age-matched controls. Assay for serum SM activity may provide a useful and simple procedure fo differentiating the cause of growth disorders from growth hormone deficiency.