Use of polyestradiol phosphate and anti‐17β estradiol antibodies for the localization of estrogen receptors in target tissues: A critique

Polyestradiol phosphate (PEP) has been used for localization of estrogen receptors in human carcinoma. The nature of PEP binding to the receptor molecule and the ability of antiestradiol antibodies to react with estrogen receptor complexes were investigated, using an animal model system. Castrated adult female rats were injected with PEP, estradiol 17βdiethylstilbestrol or saline. An estrogen target organ (uterus) and a non‐target organ (diaphragm) were removed from each animal. In each organ, unoccupied cytosolic estrogen receptors were quantified by DCC assay. The tissue sections were processed to ascertain the PEP binding and the ability of antiestradiol antibodies to detect hormone‐occupied sites. Comparison of the results obtained by DCC assay and immunohistochemical technique revealed that antiestradiol antibodies do not react with estradiol receptor complexes formed in vitro or in vivo; that PEP cannot compete with estradiol for the receptor sites in vitro; and that PEP binds to proteins other than those measured by DCC as receptor molecules having high affinity for estradiol.