Uterine estradiol and progesterone receptor concentration, activities of certain antioxidant enzymes and dehydrogenases and histoarchitecture in relation to time of secretion of nidatory estrogen and high endometrial sensitivity in rat.

Alterations in uterine nuclear and cytosolic estradiol (ER) and progesterone (PR) receptor concentration, activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), glucose-6-phosphate dehydrogenase (G-6-PDH) and lactate dehydrogenase (LDH), surface and transmission electron microscopy and histology in relation to the time of secretion of nidatory estrogen and the onset of endometrial sensitivity in the rat were investigated. A significant increase in plasma estradiol (E2) concentration in control rats was observed at 22.00 h on day 4 post-coitum, whereas progesterone (P) concentration increased at 17.00 h on day 4 and was maintained until 17.00 h on day 5. The period of high endometrial sensitivity (10.00 h on day 5) was characterized by elevated uterine cytosolic ER and nuclear and cytosolic PR concentration and POD activity, low columnar luminal epithelium with undulating surface and intercellular membranes, covered with short microvilli and pinopods, and containing numerous electron-transparent apical vesicles, mitochondria, polyribosomes, rough (RER) and smooth (SER) endoplasmic reticulum, well developed Golgi, few lysosomes and lipid droplets and loose edematous antimesometrial stroma. Inhibition in endometrial sensitivity by post-coital centchroman was associated with a marked depletion in uterine cytosolic ER and an increase in nuclear ER concentration, a decrease in POD and G-6-PDH activities, compact fibroblastic stroma, an increase in luminal epithelial cell height with decreased RER, SER, polyribosomes, Golgi, straightening of intercellular membranes, reduced surface undulations and absence of pinopods. Electron-transparent vesicles appeared flattened and clumped in the apical portion of cells, tight junctions were more prominent and lipid droplets were translucent. Nuclear and cytosolic PR and the pattern of secretion or plasma E2 and P remained unaffected. CAT, SOD and LDH activities, although high throughout pre-implantation, did not vary in relation to the secretion of nidatory estrogen, endometrial sensitivity or centchroman treatment.