Insulin-like growth factor-I and insulin-like growth factor binding protein-3 inhibit involution of the mammary gland following lactation: Studies in transgenic mice

The role of the insulin-like growth factor system on mammary gland development and involution following pregnancy and lactation was studied. Transgenic mice expressing rat IGF-I and human IGFBP-3 specifically in the mammary gland tissue, were created using the whey acidic protein gene. Mammary gland development was normal in transgenic animals expressing either rIGF-I or hIGFBP-3. In contrast, involution of the gland was delayed in both groups of transgenic mice. Specifically, the number of apoptotic cells was less in the involuting glands of transgenic mice compared with control animals. These results confirm the hypothesis that the IGF system regulates mammary gland function.