Somatomedin (insulin-like growth factor)


It as found in the early 1950s that growth hormone seems to mediate its action through an intermediary molecule. It was only recently found to be somatomedin which has now been relabelled insulin-like growth factors (IGF and IGF2). Recent studies show that these molecule are similar to insulin and that they sometimes share similar receptors. It was also shown that they are ubiquitous in the fetus. Recent studies have also shown that they mediate fetal growth. Their mediation is of paracrine-autocrine nature since unlike insulin they are not produced in a single organ. Other large biological hormones like prolactin, melanocyte stimulating hormone have been shown to aid fetal growth although minimally.

These are substances that potentiate the effect of growth hormones. There are two types, IGF1 an IGFII. They are all under the control of hormones like insulin, growth hormone, and thyroxin in the fetus. They are potent mitogens for cells which are derived from all primitive germ layers. In postnatal life they are of importance in longitudinal skeletal growth through a stimulation of chondrocyte proliferation and also the maturation of epiphyseal growth plate. It has been shown that although the main source of IGF is the liver, in postnatal life, it is also found as tissue mitogen in most body tissues.


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