Cyclic changes in the ampulla of the rat oviduct

Rats with regular 5-day estrous cycles were sacrificed on different days of the cycle and the ampullae of their oviducts were excised, fixed in glutaraldehyde, stained with uranyl acetate and lead citrate, and examined using electron microscopy. Since the ampullae undergo changes in their gross morphology during each estrous cycle, an attempt was made to correlate those changes in morphology with cyclic changes in ultrastructure of the cells and with cyclic physiological events. During the course of the estrous cycle, there were changes in the relative numbers of secretory and ciliated cells in the ampullae; secretory cells increased in numbers at estrus, became the dominant cell type at metestrus, and became rare at diestrus-1, a day on which ciliated cells prevailed. On the remaining days of the cycle both cell types were evident with more secretory cells seen at diestrus-2 and more ciliated cells seen at proestrus. The secretory cells exhibited two phases of secretion, one in which vesicles were seen to bleb from their surfaces at estrus and another in which dense granules accumulated at the apices of the cells at metestrus, only to disappear by the following day. Evidence of fluid resorption between the days of estrus and metestrus was seen. The days in which the secretory cells of the ampullae exhibited morphological changes indicative of increased activity, the days of estrus and metestrus, were the days in which oocytes can be found in that portion of the oviducts.