Insulin-Like Growth Factor-I: Compartmentalization Within the Somatotropic Axis?

Andrew A. Butler 1 , Shoshana Yakar 2 and Derek LeRoith 2 1 The Vollum Institute, Oregon Health Sciences University, Portland, Oregon 97201; and 1 Clinical Endocrinology Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-1758 Insulin-like growth factor-I (IGF-I) is essential for normal growth; igf-1 gene mutations are associated with extreme growth retardation in mice and, very rarely, in humans. The relative contributions of tissue vs. endocrine (hepatic) IGF-I to the regulation of growth has been a fundamental question. New gene targeting technologies are providing answers for these questions.