Paracrine functions of somatomedins.

Evidence is growing that the somatomedins act by a paracrine and/or autocrine mechanism. The importance of these mechanisms relative to the traditional endocrine actions is not clear, and it is possible that these growth factors act through all three mechanisms. Supporting the possible paracrine/autocrine mechanisms are reports that production of somatomedins or somatomedin-like peptides is widespread throughout the body. Additionally, the somatomedins have biological actions on remarkably diverse cell types, and these responsive cells are found in close proximity to cells known to produce somatomedin. Finally, factors that alter the growth rate of cultured cells produce parallel changes in somatomedin secretion, suggesting that these phenomena are closely linked.