Retarded administration of an antagonist stops steroid hormone action

Retarded (up to 6 h) administration of tamoxifen, an estrogen antagonist, was found to inhibit the estradiol benzoate induced responses of the chicken magnum (tissue growth, accumulation of cytoplasmic progesterone receptor and of total cellular estrogen receptor, rate of ovalbumin synthesis) measured at 24 h post-estrogen. This inhibition is apparent only after 4 h following the administration of tamoxifen. These results exclude long-lived intermediary component (s) necessary and sufficient for expression of the estrogenic responses, but are compatible with the involvement of such intermediary component (s) having relatively short half-life.