The immunocytochemical localization of a cat uterine protein that is estrogen dependent (CUPED

An estrogen-dependent polypeptide (CUPED), which was purified from uterine flushings of estrogen-treated cats, was localized in endometrial epithelial cells of cats using the peroxidase-anti-peroxidase immunocytochemical staining procedure. Epithelial cells from animals treated with estradiol for 4, 7, or 14 days and estrogen-primed animals treated with progesterone for 2 days showed positive immunostaining. Staining was absent in untreated ovariectomized animals and in estrogen-primed animals treated with progesterone for 4 days. Specific cytoplasmic staining was confined to apical secretory granules in nondiiated cells of deep uterine glands. Staining was also commonly observed in the lumen of deep glands. Immunostaining was absent in the cells of the surface epithelium, stroma, and myometrium. In addition, other organs such as the oviduct, kidney, liver, pancreas, and lung showed no evidence of specific immunocytochemical staining. Therefore, the estrogen-dependent polypeptide obtained from uterine flushings of estrogen-treated ovariec-tomized cats is a uterine-specific secretory product that is packaged in apical cytoplasmic granules of uterine epithehial gland cells before being released into the uterine lumen