IN-SITU LOCALIZATION OF PROGESTERONE RECEPTORS IN NORMAL MOUSE MAMMARY-GLANDS - ABSENCE OF RECEPTORS IN THE CONNECTIVE AND ADIPOSE STROMA AND A HETEROGENEOUS DISTRIBUTION IN THE EPITHELIUM

In normal mammary glands of both rodents and humans, progesterone prom otes the proliferation of epithelial cells and several lines of eviden ce suggest that this action of progesterone may be mediated by progest erone receptor (PR). It is well established that normal mammary develo pment involves a complex interplay between the epithelial cells and th e surrounding fatty stroma. Furthermore, during mammary development, t here is a change in both the relative proportion of epithelial cells a nd the steady-state levels of PR. Therefore, towards understanding the precise role of PR in mammary development, we have generated a highly sensitive antibody against mouse PR and examined its pattern of local ization. Immunoreactive PR was detected only in the epithelial cells o f the ducts while both the adipose and fibrous stroma surrounding thes e ducts were receptor negative. Similarly, PR mRNA was also associated only with the ductal epithelial cells. Approximately only 45-50% of t he ductal cells were receptor positive and this distribution remained unchanged whether or not the tissues had been exposed to estrogen, sug gesting that they may represent a distinct subpopulation. The potentia l significance of these findings to mammary development is discussed. (C) 1997 Elsevier Science Ltd. All rights reserved.