Cellular and subcellular localization of (3H)-progesterone and its metabolites in rat uterus studied by autoradiography

Changes in uterine surface epithelium of rat during pregnancy

The first site of attachment of the trophoblast to the uterus in rodents is on the antimesometrial side and the inner cell mass is oriented mesometrially. The present study was performed with a view to study if comparable changes occur on both the mesometrial and antimesometrial side during early pregnancy in the rat using the scanning electron microscope. The results showed three types of ectoplasmic projections: namely, (i) a smooth surface and a narrow base; (ii) many folds and pits; and (iii) a ruffled surface and broad base, seen in clusters and located at intervals on the antimesometrial side only. The results suggest that these projections with ruffled surfaces may play a role in adhesion of the blastocyst and localisation of implantation sites in the rat.

Localization of a synthetic progestin in the reproductive organs of the female baboon

The uptake and retention of a radiolabeled synthetic progestin, ORG 2058, was studied in the female reproductive system of the baboon. Four estrogen-primed baboons were injected intravenously with 2.5 micrograms/kg body weight of 3H-ORG 2058. One animal, which served as a control, received an additional injection of 2.5 mg/kg body weight of unlabeled progesterone. One hour after the injections, the animals were killed and the uterus, cervix, oviduct, vagina, and labia were removed and processed for autoradiography. The cells in the germinative layers of the stratified squamous epithelium of the cervix, vagina, and labia demonstrated nuclear localization of the label. The columnar epithelium, both surface and glandular, of the uterus and cervix sequestered the synthetic steroid; however, the nuclei of the epithelium lining the oviduct were unlabeled. The nuclei of the fibroblasts and of the smooth muscle cells were labeled in all the organs studied. These preliminary observations suggest that there is a stage in the reproductive cycle in which progesterone receptors are contained in the stromal cells of the oviduct but are absent in the epithelium.

Radioautographic study of the rat brain, uterus and vagina after [3H]R-5020 injection

Localization of [3H]R-5020, a potent synthetic progestin, was examined by radioautography in the central nervous system and the genital tract of estrogen-primed, ovariectomized rat. In the brain, a concentration of radioactivity was found in the nuclei of neurons localized in different specific areas: the preoptic region and the medio-basal hypothalamus. In the anterior pituitary, cells which concentrated the hormone were found. The uterine tissues (uterine horns and cervix) presented a nuclear concentration of radioactivity in stromal and muscle cells but little or no radioactivity in luminal and glandualr epithelia. In the vagina of the same animals, radioactivity was observed in the connective tissue cells, muscle cells and epithelial cells. Hormonal specificity and saturability of radioactivity binding in these target tissues were established by competition with an excess of unlabeled hormones. In the presence of an excess of unlabeled progesterone the nuclear concentration of radioactivity was diminished in all areas, while no inhibition of radioactivity incorporation was observed with unlabeled corticosterone. These results suggest the presence of specific progesterone receptors in the hypothalamus, the pituitary and the genital tract tissues of the rat.

Regional differences between nuclear concentration of (3H) estradiol and (3H) progesterone and their action on the uterus of rat during delayed implantation

The cellular and subcellular localization of radioactivity by dry-mount autoradiography was studied at 5, 15 and 30 minutes after intraluminal or at 5, 15, and 60 minutes after subcutaneous administration of (3H) estradiol or (3H) progesterone to rats in which implantation was delayed by ovariectomy on day 3 post-coitum, followed by treatment with progesterone. After intraluminal instillation of (3H) estradiol or (3H) progesterone, radioactivity was cleared from the uterine lumen at 5 minutes. After intraluminal as well as subcutaneous injection of (3H) estradiol, radioactivity was concentrated at all time intervals in the nuclei of cells of the substantia propria, glands and muscularis, but not in the luminal epithelium. White blood cells and endothelial cells were unlabeled, while perivascular cells showed concentration of radioactivity. After intraluminal instillation of (3H) progesterone, radioactivity was retained in the cytoplasm of the luminal epithelium at 5 and 15 minutes, while no such concentration appeared after subcutaneous injection. No selective nuclear retention was observed in the luminal epithelium, in contrast to the substantia propria and muscularis. The autoradiographic results indicate that progesterone treatment simulating the conditions of early pregnancy, changes the uptake affinity of uterine tissues for (3H) estradiol. The lack of a detectable concentration of estrogen within nuclei of the luminal epithelium does not preclude hormone action. Possible mechanisms of metabolic activation of the uterine luminal epithelium in the apparent absence of concentration of (3H) estradiol to nuclei of the luminal epithelium are discussed.

Quantitative studies of the effect of progesterone on endometrial morphology of the spayed rat

The effects of various dosages and of various time periods of treatment with progesterone have been studied in the spayed, mature rat. Test objects were the cells of the luminal epithelium and of the endometrial stroma which were examined by qualitative and quantitative electron microscopy. No significant response was observed in epithelial or stromal cells until after 12 hrs of progesterone treatment. The nuclei of both cell types were then more circular than earlier with reduced long diameters. The functional significance of this change in configuration is unclear since only in the stromal cells was it followed by nuclear growth. Further, after 12 hrs of treatment the relative amounts of mitochondria and granular endoplasmic reticulum of stromal cells were reduced while the volume of the stromal cell cytoplasm appeared enlarged. This is taken as evidence that progesterone causes an intracellular oedema probably by decreasing cell membrane permeability. This response is probably not specific for the stroma but also includes the luminal epithelium, although the volume of the epithelial cell cytoplasm could not be determined here. Nucleolar enlargement did occur in stromal cells and was observed after 12 hrs of treatment but was not significant until after 24 hrs. At this point of time the net amount of granular endoplasmic reticulum in stromal and epithelial cells was increased indicating an increased protein synthesis in both cell types. However, only in the stromal cells was this associated with nucleolar enlargement, which supports the idea that progesterone stimulates protein synthesis through different mechanisms in the two cell types. Testing various dosages of progesterone showed that 0.5 mg had an effect similar to 5 mg of progesterone. When 0.05 mg progesterone was injected the only effect observed was an increase in the amount of apical vesicles of the luminal epithelium, showing that the epithelium is more sensitive to progesterone than the stroma.

Neurons of the hypothalamus concentrate (3H)progesterone or its metabolites

Selective concentration of [(1)H]progesterone or its metabolites is observed in nuclei of neurons in certain hypothalamic regions of the guinea pig 15 minutes after injection of [1,2,6,7-(3)H]progesterone, by use of dry-mount autoradiography. Highest concentrations of progestin target neurons exist in the nucleus arcuatus, the nucleus preopticus periventricularis, and the nucleus preopticus suprachiasmaticus. Previous administration of unlabeled progesterone inhibits the nuclear concentration of radioactivity, but cortisol has no effect. Estradiol priming enhances the nuclear uptake of radioactivity. The results demonstrate the existence of progestin target sites in the hypothalamus and suggest a direct action of progestin on certain hypothalamic structures.