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Changes in secretory status, cell height and percentage ciliation of epithelial lining of sheep fimbria oviduct during early pregnancy

Studies have shown that the biosynthetic activity of the fimbria oviduct in the sheep changes during the first few weeks of pregnancy. The objective of the present study was to determine whether the secretory epithelial lining of the fimbria undergoes pregnancy-associated morphological alterations in a concordant manner. Oviducts obtained from ovariectomized, oestrous (day 0) and pregnant (day 1.5, 2, 3, 4, 6 and 16) ewes were analysed quantitatively and qualitatively using light and electron microscopy. The epithelium was low cuboidal in fimbria from ovariectomized sheep, significantly increased in height at day 1.5 of pregnancy, immediately decreased at day 2, and underwent an additional slight reduction at day 6 and day 16 of pregnancy. Ciliated and nonciliated cells were present in the epithelium at all reproductive stages. The proportions of ciliated and nonciliated cells varied during pregnancy and ciliated cells were always the major cell type. Consistent with previous data, the secretory organelles of nonciliated epithelial cells obtained from ovariectomized ewes were poorly developed. Maturation of secretory organelles in nonciliated cells occurred at oestrus and was maintained until days 2–3 of pregnancy; regressive changes were then observed, characterized by atrophy of the Golgi apparatus and rough endoplasmic reticulum, and increases in heterochromatin and pronounced nuclear folds. Large, electron-dense lipid droplets were present throughout the cytoplasm of ciliated and nonciliated epithelial cells, beginning at day 1.5 of pregnancy and increasing at later stages of pregnancy. Apical protrusions and microvilli were observed at the luminal domains of nonciliated cells and were reduced in extent after day 3 of pregnancy. Cells were extruded from the epithelial lining at day 16 of pregnancy. These data show that the epithelial lining of the fimbria oviduct in the sheep undergoes distinct changes in cell height, percentage ciliation and secretory organelle development during the first few weeks of pregnancy.