Ultrastructural changes in the oviductal epithelium of merino ewes during the estrous cycle

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Abstract
Isthmic and ampullary oviductal epithelia sampled from Merino ewes at days ‐1, 1, 3, and 10 of the estrous cycle (estrus = day 0) were studied by scanning and transmission electron microscopy after fixation by vascular perfusion. Secretory cells, ciliated cells, and lymphocytelike basal cells were observed in both isthmic and ampullary epithelium at all stages of the estrous cycle studied and their ultrastructural features were analyzed. Synthesis of lamellated secretory granules occurred in the ampullary secretory cells during the follicular and early luteal phases, and their contents were released by exocytosis into the oviductal lumen during the luteal phase. Granule release was associated with nucleated apical protrusion of these cells into the oviductal lumen. No such secretory activity was displayed by isthmic secretory cells even though a few cells contained nonlamellated granules. Apocrine release of apical vesicles and accompanying cytoplasmic material from apical protrusions of ciliated cells occurred in the isthmus around estrus but not in the ampulla. This unexpected feature has not previously been reported in any other mammal. Dendritic basal cells were distinguished in the lower part of the epithelium by their heterochromatic nuclei, electron‐lucent cytoplasm, and lack of attachment zones. No migration of basal cells was observed, and their ultrastructural features were similar in the ampulla and isthmus and at all stages of the estrous cycle examined. The function of these lymphocytelike cells in the epithelium is uncertain, but the presence of phagocytic bodies and lysosomes in 20% of them may indicate a phagocytic role.