Epithelial lining of the sheep ampulla oviduct undergoes pregnancy-associated morphological changes in secretory status and cell height.

The biosynthetic activity of the sheep ampulla oviduct changes during the first few days of pregnancy. An estrogen (E2)-dependent glycoprotein (M(r) 90,000-92,000) is expressed, synthesized, and released when fertilization and embryo development occur in the oviduct. The objective of the present study was to determine whether the secretory epithelial lining of the ampulla, the cellular source of the E2-dependent protein, undergoes morphological alterations during early pregnancy is a contemporaneous manner. Ampulla oviducts obtained from ovariectomized (ovx), estrous (Day 0), and pregnant (Days 1.5, 2, 3, 4, 6, and 16) ewes were analyzed with light and electron microscopy. The mean cell height of epithelial cells from estrus and from Days 1.5, 2, and 3 of pregnancy was significantly (p < 0.05) higher than in ovx animals. A significant reduction in cell height was observed at Day 4 of pregnancy, and this value remained unchanged at Day 6 and Day 16. Ciliated and nonciliated cells were present in the ampulla at all stages examined, with ciliated cells constituting the major cell type. Consistent with previous results, the nonciliated cells obtained from ovx ewes were synthetically inactive and at estrus were characterized by well-developed secretory organelles, including abundant amounts of secretory granules containing the E2-dependent glycoprotein. Extensive microvilli and cytoplasmic blebs protruding into the oviduct lumen distinguished the apical surface of secretory epithelial cells until Day 3. At Day 1.5 the secretory cells contained dilated cisternae of rough endoplasmic reticulum and enlarged Golgi, which were progressively diminished with increasing stages of pregnancy. Exocytosis, fusion of secretory granules, and a reduction in their electron density were seen until Days 3-4. By Day 4 and Day 6, fewer granules were observed in the ampulla cytoplasm and few, if any, were present by Day 16. Increases in the amount of heterochromatin were seen in nuclei at Day 6 and Day 16. Extrusion of epithelial cells into the oviduct-lumen was evident at Day 16 of pregnancy. These data show that 1) the secretory epithelium of the sheep ampulla oviduct undergoes morphological alterations in protein-synthesizing organelles and apical specializations that vary with the stage of pregnancy, 2) the secretory product contained in lamellar granules is released by the process of exocytosis until Days 3-4, and 3) cell death appears to occur at Day 16 by shedding of epithelial cells into the oviduct lumen.