Rat strain-specific effects of 17β-estradiol on protein expression. Representative western blots of protein lysates prepared from mammary glands of ACI and BN rats, treated with E2 for 1, 3 or 12 weeks, and probed with antibody to Spp1 (Panel A), Lcn2 (Panel B) or β-actin (Panel C). The amounts of Spp1 (Panel D) and Lcn2 (Panel E) were quantified using a LI-COR Odyssey system and expressed relative to the amount of β-actin in the same lysate. Representative western blots of protein lysates prepared from mammary glands of ACI and BN rats, treated with E2 for 12 weeks, and probed with antibody to Mmp7 (Panel F), Mmp9 (Panel G) or β-actin (Panel H). The amounts of the proenzymes and active forms of Mmp7 (Panel I) and Mmp9 (Panel J) were quantified using a Bio-Rad ChemiDoc XRS + imaging system and expressed relative to the amount of β-actin in the same lysate. Each data bar represents the mean ± SEM, n = 3 biological replicates. 1, p < 0.05, E2 treated vs. sham treated rats of same strain. 2, p < 0.05, E2 treated BN rats compared to E2 treated ACI rats.