Immunohistochemical localization of estrogen receptor in the normal canine female genital tract.

The distribution of estrogen receptor (ER) in the ovaries and uterus was studied throughout the estrous cycle in the bitch. The stage in the estrous cycle of 25 dogs was assessed by gross and histologic appearance of the uterus and ovaries and blood steroid hormone values. Demonstration of ER was performed by an indirect immunohistochemical technique with monoclonal antibodies. ER was found as a red nuclear staining in the surface, crypt, and glandular epithelium; in endometrial stroma cells; and in smooth muscle cells of the tunica muscularis of the uterus. Total scores of ER-positive cells varied during the estrous cycle, with the highest scores in the early proliferative stage and the lowest scores in the early secretory stage of the estrous cycle. These results are in concordance with the observations in other animals and the human uterus. In the canine ovaries, positive staining for ER was present in surface epithelium and subsurface epithelial ingrowths, which is in contrast with negative staining of human ovaries. This study confirms the earlier hypothesis that the epithelial ingrowths in canine ovaries may be responsive to blood steroid hormones.