ROLE OF EPIDERMAL GROWTH-FACTOR AND TRANSFORMING GROWTH-FACTORS IN MAMMARY DEVELOPMENT AND LACTATION

Epidermal growth factor, transforming growth factor-alpha, and transforming growth factor-beta1 are potent effectors of mammary growth that work in concert with endocrine hormones, such as estrogen, progesterone, corticosteroids, and prolactin. Estrogen and progesterone stimulate production of epidermal growth factor or transforming growth factor-alpha to stimulate mammary growth. Epidermal growth factor and prolactin synergize in whole organ culture to cause lobulo-alveolar development and to alter the profile of synthesized milk proteins. Transforming growth factor-beta1 inhibits mammary development of prepubertal mice. However, once the gland is committed to differentiation, transforming growth factor-beta1 no longer affects mammary morphogenesis. The role of transforming growth factor-beta1 in milk protein synthesis is unknown. Transforming growth factor-alpha and -beta1 mRNA have both been identified in the mammary gland of cows. The gland has epidermal growth factor receptors, and epidermal growth factor or transforming growth factor-alpha can stimulate proliferation of mammary epithelial cells in vitro. The role of transforming growth factor-beta1 in bovine mammary tissue has not been studied. An understanding of the role of epidermal growth factor, the transforming growth factors, and their interactions with endocrine hormones will lead to a more complete understanding of how mammary development and lactation are regulated.