We performed immunohistochemical studies of chicken oviduct after different fixation procedures, by using antibodies against the progesterone receptor: polyclonal antibodies IgG-G3 against the "8S" form (an oligomere containing progesterone-binding and nonprogesterone-binding units), polyclonal antibodies IgG-RB against the progesterone-binding B subunit, and monoclonal BF4 against the non-progesterone-binding 90,000-mol-wt protein component. Chickens were immature animals with or without estrogen priming, and with or without progesterone treatment. The antibodies were revealed by means of an immunoperoxidase technique that used the avidin-biotin-peroxidase complex, and controls were performed by presaturation of antibodies with the purified 8S-progesterone receptor, the B subunit, and 90,000-mol-wt protein. The progesterone receptor was detected not only in well-characterized target tissues, i.e., in glands and luminal epithelium, but also in stromal cells (some displayed the strongest reaction), in mesothelium, and in fibers of smooth muscles. Only in cell nuclei, whether or not the animals received an injection of progesterone was an antigen revealed corresponding to the B subunit (and/or to the A subunit, because there is immunoreactivity of IgG-RB with both hormone-binding subunits A and B). The 90,000-mol-wt protein was revealed in both cytoplasm and nuclei. These immunohistological data suggest that the concept of steroid action that necessarily involves the original formation of the hormone-receptor complexes in the cytoplasm before translocation to the nucleus, may have to be revised.

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