Growth factor control of pancreatic B cell hyperplasia.

Pancreatic B cell hyperplasia is an essential feature of normal fetal and childhood development in order to maintain insulin availability to the growing organism. While glucose, amino acids and pituitary growth hormone have all been shown to increase B cell DNA synthesis in cultures of isolated islets of Langerhans, there is also evidence for a local regulation of growth by trophic factors. IGF-I and IGF-II are expressed and released by pancreatic B cells and have the capacity to act as B cell mitogens. Specific IGFBPs are also released by islets which may modulate the bioactivity of IGFs. While IGF release is not under acute nutrient control, at least in vitro, the mitogenic actions of growth hormone on islets are mediated in part by an increase in the local release of IGF-I. Other peptide growth factors reported to influence B cell DNA synthesis include PDGF, EGF, TGF-beta and TRH. The contribution of peptide growth factors to pathological abnormalities of pancreatic islet growth is unknown.