Distribution of estrogen and progesterone receptors and steroid-regulated gene products in the chick oviduct.

The distribution of estrogen and progesterone receptors (ER and PR, respectively) was studied immunohistochemically in the chick oviduct. Estrogen receptor immunoreactivity was found only in the nuclei of glandular epithelial cells. Progesterone receptor was found in the nuclei of glandular and luminal epithelia, stroma, smooth muscle cells and in the mesothelium. The dissimilar distribution of ER and PR suggests that either ER concentration in the luminal epithelium and smooth muscle is very low (below the sensitivity of ER immunostaining) or that estrogens control their PR synthesis indirectly via ER in glandular cells. A known estrogen-inducible protein, ovalbumin, was localized in the same glandular epithelial cells as ER. A progestin-inducible protein, avidin, was found in part of the luminal and glandular epithelium cells but not in other PR-positive cell types. This indicates the importance of cellular differentiation in the regulation of avidin synthesis. Estrogen and progesterone administration had effects also on ER and PR immunoreactivity. Estrogen and progesterone administrations for 24 h decreased markedly the immunoreactivity of their receptors. The decrease in receptor immunoreactivity is most likely due to a transient loss of immunoreactive receptor protein, since the antibodies (H222, PR6) react both with transformed (4 S) and non-transformed (8 S) receptor forms. At the subcellular level, PR was localized in the chromatin by immunoelectron microscopy. Progestin administration seemed to decrease PR immunoreactivity especially in the heterochromatin area, suggesting that conformational chromatin rearrangements occur during down-regulation of PR.