The biosynthesis of somatomedins and their role in the fetus.

The somatomedins are a family of hormones consisting of insulin-like growth factors 1 and 2 as well as their variant forms. These peptides have a direct growth-promoting action on fetal cells mediated through their interaction with Type I and II receptors distributed throughout the fetus. The genes for both IGF-1 and IGF-2 are expressed in the fetus. In man, the predominant forms are the truncated IGF-1 variant and IGF-2. Unlike production at maturity, fetal biosynthesis appears independent of growth hormone and may instead be primarily regulated by nutrition. Other hormones such as placental lactogen are also involved in the regulation of fetal biosynthesis of somatomedins.