[Growth factors with identical insulino-situations : IGF I and II, NSILA and somatomedins (author's transl)].

NSILA consists of two polypeptides of known structure. IGF I and II are close relatives of insulin. 50% of all amino acid residues in the A-and B-region of IGF I and II are situated in identical positions as in the A-and B-chain of insulin. A C-region of 12 and 8 residues respectively connects the A-and B-region in IG FI and II. A D-region of 8 and 6 residues extends the A-region of IGF I and II. 17 of all invariable 19 amino acid residues in the insulin molecules of all known species are also present in IGF. IGF is attached to a carrier protein in serum. The latter inhibits its action on adipose tissue and muscle. Therefore, IGF cannot be measured in serum but, rather, must be dissociated from the binding protein before quantitation. Most tissues appear to have IGF binding sites for which insulin does not compete with the exception of fibroblasts. IGF probably acts via interaction with the IGF receptor, with the exception of adipose tissue where the IGF effect is mediated by the insulin receptor. The concentration of IGF I in serum is under growth hormone control. It is elevated in acromegalics and decreased in pituitary dwarfs and Laron dwarfs. IGF I and II are potent stimulators of cell growth in culture. Their growth stimulating effect in vivo has not yet been unequivocally proven.