somatomedin

Somatomedin is the older umbrella name for the growth-promoting peptides that we now mostly call insulin-like growth factors. Think of it as the historical job title before the chemistry was fully mapped and the workers got their modern names.

The term grew out of the somatomedin hypothesis of the 1950s and 60s, which proposed that growth hormone does not act on cartilage directly but instead instructs the liver to release intermediate factors that mediate growth. These factors were named somatomedins, from soma meaning body and the idea of mediating somatotropin's action.

As biochemistry advanced, the main somatomedins were purified and renamed: somatomedin C became IGF-1 and somatomedin A is largely identified with IGF-2. Today the IGF nomenclature dominates, and somatomedin survives mostly in textbooks, older papers, and the occasional lab report.

The honest caveat is that the original strict somatomedin hypothesis was an oversimplification. We now know growth hormone also acts directly on tissues, and that many tissues make IGF-1 locally rather than depending only on liver-derived factor, so the clean manager-and-mediator picture is a useful starting model rather than the full truth.