A somatomedin is a type of peptide which is found in blood plasma and is involved in the regulation of human growth and development. They are hormones, a category of protein molecule which transports chemical signals around the body. The primary function of somatomedin peptides is to stimulate cell division and cell growth, mainly in cartilage but also in other body tissues.
Currently, there are two identified types of somatomedin, known as insulin-like growth factor I and insulin-like growth factor II. These two types have similar roles in the body, but are active at different times during the lifespan of an individual. Generally, insulin-like growth factor I is active in children and adults, whereas insulin-like growth factor II is active mainly during early pregnancy, and is one of the most important fetal growth hormones.
The liver synthesizes somatomedins. When stimulated by another growth hormone called somatotropin, liver cells release somatomedin peptides into the bloodstream. When absorbed by cartilage cells, they increase the ability of cartilage to absorb sulfate and also enhance the rate of collagen synthesis. In addition, the synthesis of RNA and DNA in cartilage cells is increased, helping to increase cell division rates. These hormones are also active in many other tissue types, including nerves, skin, bone, and muscle.
Somatomedin peptides are essential for regulating the proper growth and development of many tissue types in both children and adults. This means that abnormal levels of either of the insulin-like growth factors tends to have dramatic consequences. High levels of insulin-like growth factor II are associated with certain types of cancer, including breast, lung, liver, colon, and prostate cancer, as well as leukemia.
Another disease relating to abnormal levels of somatomedins is Beckwith-Wiedemann syndrome, caused by very high levels of insulin-like growth factor II. This leads to unusually high rates of growth and weight gain in childhood. Common symptoms include defects of the abdominal wall, overgrown abdominal organs, and an increased risk of rare cancers such as Wilms tumor of the kidneys. Up to 10 percent of children with Beckwith-Wiedemann syndrome develop at least one type of tumor, and approximately 20 percent die in childhood.
Abnormally low levels of somatomedins can also lead to disease in both children and adults. In children with symptoms such as short stature, slow growth, or delayed physical development, one possible culprit is a deficiency of insulin-like growth factor I. In adults with this type of deficiency, common symptoms can include poor muscle strength, high blood lipids, and reduction in bone density. Children and adults can be treated with growth hormone replacement therapy; in children, however, physical development might remain somewhat delayed.