= Insulin-like growth factor 1
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= IGF-1
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{synonym}
= IGF-I
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{synonym}
<Insulin-like growth factor 1> is a <peptide hormone> and growth mediator associated with <growth hormone> action. The <liver> supplies an important circulating source, and <IGF-1> signalling helps coordinate growth of tissues including <cartilage> and <bone>. The regulatory pathway therefore connects a pituitary signal with growth-related responses in other tissues.<Anatomy and Physiology 2e by J. Gordon Betts and others>[Section 17.3: Growth Hormone and Figure 17.10, liver-derived insulin-like growth factors and tissue growth]{ref}
The motivating experiment was to look for a measurable activity in <blood serum>. A 1957 report by <W. D. Salmon Jr.> and <William Daughaday> examined a hormonally controlled serum factor through <sulfate> incorporation by <cartilage> in vitro.<A hormonally controlled serum factor which stimulates sulfate incorporation by cartilage in vitro by W. D. Salmon Jr. and William Daughaday>[Publication title and bibliographic record]{ref} In his later account, <William Daughaday> described cartilage culture and sulfate uptake as the readout that motivated the hypothesis of a serum mediator of <growth hormone> action.<Growth hormone axis overview: somatomedin hypothesis by William Daughaday>[Author retrospective, abstract: cartilage assay and the serum-mediator hypothesis]{ref}
This was a functional assay: it detected what a serum preparation did to a tissue. Identifying the responsible molecules required further biochemical work. In 1978, <E. Rinderknecht> and <R. E. Humbel> reported structural homology between serum-derived <IGF-I> and <proinsulin>, providing a molecular basis for the insulin-like designation.<The amino acid sequence of human insulin-like growth factor I and its structural homology with proinsulin by E. Rinderknecht and R. E. Humbel>[Abstract: serum polypeptide and structural homology to proinsulin]{ref}
The historical progression connects three kinds of evidence: pituitary control, a tissue response to <blood serum>, and molecular identification of a <protein>. A serum bioactivity measurement and a measurement of one purified <hormone> answer different experimental questions.
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