KERATINOCYTE GROWTH-FACTOR IS A GROWTH-FACTOR FOR MAMMARY EPITHELIUM IN-VIVO - THE MAMMARY EPITHELIUM OF LACTATING RATS IS RESISTANT TO THEPROLIFERATIVE ACTION OF KERATINOCYTE GROWTH-FACTOR

Keratinocyte growth factor (KGF) is a member of the fibroblast growth factor (FGF) family. KGF is secreted by stromal cells and affects epit helial but not mesenchymal cell proliferation. KGF injected intravenou sly was found to cause dramatic proliferation of mammary epithelium in the mammary glands of rats. KGF causes ductal neogenesis and intraduc tal epithelial hyperplasia but not lobular differentiation in nullipar ous female rats. KGF causes ductal and lobular epithelial hyperplasia in male rats. KGF causes proliferation of ductal and acinar cells in t he mammary glands of pregnant rats. On the other hand, the ductal epit helium of lactating postpartum rats is resistant to the proliferative action of KGF. The mammary glands of lactating rats did not express le ss KGF receptor mRNA than the glands of pregnant rats, suggesting that the resistance of the ductal epithelium to KGF during lactation is no t related to KGF receptor mRNA down-regulation The mammary glands of b oth pregnant and postpartum lactating rats express KGF mRNA with more KGF present in the glands of lactating rats. In conclusion, the KGF an d KGF receptor genes are expressed in rat mammary glands and recombina nt KGF is a potent growth factor for mammary epithelium.