Cyclic ultrastructural changes in ewe uterine tube (oviduct) infundibular epithelium

Ultrastructural features of the uterine tube (oviduct) infundibulum of ewes have been studied, with special reference to cyclic changes in the ciliated and the secretory cells. Tissue from the uterine tube infundibulum was taken from 12 Rambouillet crossbreed ewes which were killed at intervals (days 1 (or estrus), 3, 9, 10, 12, and 16) throughout the estrous cycle. The presence of cilia was demonstrated throughout the estrous cycle, and true degeneration or loss of cilia was not apparent at any phase of the cycle. Presence of fibrous granules, which are supposedly related to basal body replication, was demonstrated in the apical cytoplasm of ciliated cells on day 1 of the estrous cycle. Small ciliary buds were especially present on day 1, indicating active formation of cilia during the follicular phase of the cycle. The presence of fibrous granules, basal bodies, and ciliary buds at estrus indicates that ciliogenesis in the ewe uterine tube is stimulated by high levels of endogenous estrogen. Rootlets were observed both during the follicular and the luteal phases of the cycle. The rootlets were about 1 mum long, and their fine structure indicates that they might function as anchoring structures for the motile cilia. The most striking feature during estrus was the occurrence of glycogen granules in the cytoplasm of ciliated and secretory cells. These granules were in the apical cytoplasm and basal region of some epithelial cells. They were minimal or absent during the luteal phase of the estrous cycle. The presence of electron-dense glycogen particles was clearly demonstrated within basal bodies. Possibly the glycogen within the basal bodies functions as a source of energy for ciliary movement and the cytoplasmic glycogen as nourishment for the ovum. The secretory cells also showed characteristic cytologic changes which were correlated with the phase of the estrous cycle. Maximal secretory cell differentiation was apparent during the follicular phase, at which time these cells were characterized by well-developed rough endoplasmic reticulum, numerous ribosomes, and secretory granules of varied size, shape, and density. A most remarkable feature of the granules was their membranous structure, consisting of concentric lamellae of equal dimensions. Typical extrusion of secretory granules into the tubal lumen was apparent during the follicular and the luteal phases of the estrous cycle. Cytoplasmic projections containing nuclei protruded into the tubal lumen and some were free in the lumen, especially during the luteal phase of the estrous cycle. The presence of a well-developed endoplasmic reticulum and numerous secretory granules during estrus indicate that secretion in the ewe uterine tube is presumably under the control of circulating high plasma concentrations of estrogen.