The Pivotal Role of Insulin-Like Growth Factor I in Normal Mammary Development

Abstract

Mammary development begins in puberty in response to an estrogen (E 2) surge. E 2 does not act alone. It relies on pituitary growth hormone (GH) to induce insulin-like growth factor I (IGF-I) production in the mammary stromal compartment. In turn, IGF-I permits E 2 (and progesterone) action. During puberty, E 2 and IGF-I synergize for ductal morphogenesis. During pregnancy, progesterone joins IGF-I and E 2 to stimulate secretory differentiation necessary to produce milk. Prolactin stimulates milk production, while transforming growth factor-β inhibits proliferation. The orchestrated action of hormones, growth factors, and receptors necessary for mammary development and function are also critical in breast cancer. © 2011.