The Somatomedins: A New Class of Growth-Regulating Hormones?

Although growth hormone (somatotrophin) is generally regarded as the principal hormone regulating skeletal growth, evidence has accumulated that growth hormone does not itself stimulate linear growth, but rather induces the formation of a secondary growth-promoting factor. In recent years rapid progress has been made in characterizing this elusive growth factor. Although originally designated "sulfation factor" (because it stimulates the incorporation of radioactive sulfate into glucosoaminoglycans of cartilage), this factor has recently been found to play a much more profound role in cell growth than initially suspected. For this reason, investigators from three countries recently proposed that the operational term, "sulfation factor," be discarded in favor of the more generic name, "somatomedin".1 The prefix "somato" connotes the hormonal relationship to somatotrophin, whereas the suffix "medin" indicates that somatomedin is an intermediary in growth hormone action. Evidence has subsequently been obtained that plasma contains more than one growth-promoting substance under growth hormone