Investigation of mouse mammary ductal growth regulation using slow-release plastic implants

Mammary ductal development in the mouse is now thought to depend on an interplay of locally produced (glandular) and systemic mammogens. A novel plastic implant material, ethylene vinyl acetate copolymer (Elvax 40P), capable of the slow-release of undenatured, bioactive molecules in situ, now enables treatment of small regions of the mammary gland for extended periods with hormones and growth factors. Here we describe results obtainable with this technique. Specifically, the classical mammogens, estrogen, growth hormone, and prolactin, as well as the nontraditional mammogens, epidermal growth factor and cholera toxin, were shown to stimulate ductal growth in zones around an implant in ovariectomized animals. The possibility that these observations reflect the existence of multiple mammogenic pathways is discussed.