Lactoferrin is an estrogen responsive protein in the uterus of mice and rats

To identify lactoferrin (LF) and determine its estrogen-responsiveness in the rat uterus, immature Sprague-Dawley rats were untreated or subcutaneously injected with 17beta-estradiol (500 microg/kg) for 3 days and uterine tissues collected. Outbred immature CD-1 mice, treated with 17beta-estradiol, provided the positive control. By using a polyclonal antibody raised against mouse LF, minimal detectable protein was immunolocalized in uterine epithelial cells of untreated immature rats and mice. After estrogen treatment, LF was localized in all uterine epithelial cells of both species, although staining was more intense in mice than rats. In mice, LF was evenly distributed throughout the cytoplasm with intense staining in some cells, while in rats, it was seen mainly in the apical cytoplasm. For comparison to another well-known estrogen responsive protein in rats, complement C3 was immunolocalized within epithelial cells and it showed a different staining pattern than LF. Uterine tissue homogenates were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blots showed cross-reactivity with the mouse LF antibody. These findings indicate that LF is present in the rat uterus, and is induced by estrogens as reported in other species. Thus, LF is an important marker of estrogenic activity across species and will, therefore, have utility in screening for effects of environmental estrogenic compounds.