Abstract
Three separate lines of research, initially perceived as unrelated, have converged to form the present field of the somatomedins and the insulin-like growth factors (see (1,2) for early reviews). Because these separate areas of research evolved their own terminology, there is a confusing array of names for the different factors under study. The first of these areas of research was based on the observation that a key target tissue of growth hormone in vivo responsible for the skeletal growth, namely cartilage, is not responsive to growth hormone in vitro. This tissue, however, is highly responsive to a GH-dependent factor in serum originally given the operational designation of “sulfation factor,” because it was convenient to monitor the response by measuring sulfate uptake into cartilage. Later when extracts containing this factor were shown to evoke pleiotypic responses in cartilage and certain other tissues, the less restrictive term, “somatomedin,” was introduced. Subsequent fractionations yielded three preparations believed to have somatomedin activity: a neutral fraction designated somatomedin A, an acidic fraction, somatomedin B, and a basic fraction, somatomedin C.
The second contributing line of research was based on the observation that only a relatively small fraction of the insulin-like action of serum on fat and muscle tissue in vitro could be neutralized by anti-insulin serum. Much of this nonsuppressible insulin-like activity (NSILA) could be extracted in acid-ethanol and was designated NSILAs (the subscript stands for soluble), and the residual activity was insoluble and was called NSILAp. When purification progressed further to show two separate fractions with NSILAs activity, they were called NSILAs-I and NSILAs-II.
The third line of research contributing to this field arose from attempts to determine the constituents of bovine serum which stimulated cell division and growth of fibroblasts in culture.
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