ABSTRACT
Insulin-like growth factor I (IGF-I) is a basic polypeptide structurally related to pro-insulin. IGF-I is virtually ubiquitous in the body, partly because it is transferred to target organs through blood circulation and partly due to its peripheral production. IGF-I activity on breast epithelial cells could be mediated through the following mechanisms: local production by the same cells on which it will then exert its activity; production by a part of the surrounding stromal tissue; and transfer through blood circulation. During the menopause, plasma levels of IGF-I and a specific binding proteins are significantly modified by hormone replacement therapy (HRT); it is now ascertained that the effects of HRT on the growth hormone and IGF-I axis vary according to the route of administration of estrogens, or to the association with progestins, which differ as far as metabolic properties and doses are concerned.
