Immunocytochemical localization of estrogen receptors in spontaneous and experimentally induced canine benign prostatic hyperplasia

Abstract

Estrogens are believed to play a critical role in the etiology of canine benign prostatic hyperplasia (BPH); however, the mechanism has not been elucidated. To gain insight into this problem, we investigated the immunocytochemical localization of estrogen receptors (ER) in normal prostates, spontaneous BPH, and experimentally induced BPH by using a monoclonal ER antibody (H222). In all canine prostates the majority of ER was localized in nuclei of the same histological components: (1) transitional epithelium and subjacent stroma of the prostatic urethra, (2) periurethral prostatic ductal epithelium, and (3) prostatic stroma. ER content in the stroma was highest in the periurethral region of the prostate. Among the different groups of dogs, differences in ER location were seen only in the glandular epithelium. No ER was found in the glandular epithelium of normal prostates of young untreated dogs. In striking contrast, glandular epithelium of spontaneous BPH contained specific nuclear ER staining, though this staining was heterogeneous and was observed in only a minority (less than 10%) of the acinar epithelial cells. ER-positive acini in BPH were located predominantly in the periurethral region. These data demonstrate anatomical and biochemical heterogeneity of prostatic components and indicate that the estrogen sensitivity of prostatic cells is heterogeneous. If estrogen does play a role in BPH, it appears to act selectively rather than uniformly throughout the prostate. We reasoned that if glandular epithelial ER are involved in the development of spontaneous BPH, one might expect to find the same location of ER in BPH that was induced experimentally by specific types of treatment with androgens +/- estradiol. However, among hormone-treated dogs the presence of ER-positive prostatic glandular epithelium varied with the type of hormonal treatment but did not correlate with the experimental induction of glandular BPH. Some treatment groups with induced BPH had ER-positive prostatic glandular epithelial nuclei (with the same extent and pattern of ER localization as in spontaneous BPH); however, other treatment groups with induced BPH had ER-negative glandular epithelium. These data indicate either that glandular epithelial ER may not be involved in the pathogenesis of canine BPH or that there may be different types of BPH that have different etiologies. Possible mechanisms by which estrogen may affect the canine prostate are discussed in light of these new data on ER location.