Estrogen Regulation of the Pituitary Insulin - Like Growth Factor System
Insulin-like growth factor I (IGF-I) and the closely related IGF-II are homologous to proinsulin and share many of insulin’s effects on cell metabolism. In addition they stimulate cellular differentiation and proliferation1. Circulating IGF-I originating mainly from the liver, has classical endocrine actions2, however, local IGF-I production in many other tissues suggests an autocrine/paracrine role as we113. Most biological actions of the IGFs are mediated through the IGF-I receptor (IGFR-I) which has intrinsic tyrosine kinase activity4,5 Specific, high-affinity, insulin-like growth factor binding proteins (IGFBPs), present in the plasma and extracellular space, also bind the IGFs, modulating their interaction with the IGF-I receptor and perhaps targeting IGFs to specific loci6. To date, six different IGFBPs have been characterized7, among which IGFBP2 is particularly abundant in the pituitary8.
KeywordsEstrous Cycle Anterior Pituitary
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