PR expression in mammary glands treated with progestins for 2 months: Western blot studies. Mammary glands from the same groups shown in Figure 4 were processed to obtain nuclear extracts (as explained in Materials and methods) and used in Western blots. (a) A representative experiment using C-19 PR Santa Cruz antibody is shown. Because different amounts of epithelial cells are present in the different extracts, the (b) ratio of PR-A/PR-B in three different experiments is shown. *P < 0.05, **P < 0.01, ***P < 0.001 treated versus control. PR, progesterone receptor.