Human fetal cartilage response to plasma somatomedin activity in relation to gestational age

The response of human fetal costal cartilage (gestational age 12--25 weeks) to plasma containing somatomedin activity has been examined in vitro. Uptake of both 3H-thymidine and 35S-sulfate into the cartilage was increased; the increase in 35S-sulfate uptake was relatively constant (mean = 198% of basal, N = 25) throughout the period studied; however, the increase in 3H-thymidine uptake varied with gestational age, reaching a maximum of about 200% at 15--17 weeks and decreasing thereafter. Such a change in cartilage sensitivity to somatomedins could be an important feature in the pattern of skeletal growth of the human fetus during gestation. The data do not confirm that human cartilage is most sensitive to somatomedins during intrauterine life.