Fine structure of rat uterine eosinophils and the possible role of eosinophils in the mechanism of estrogen action

The uterine eosinophil binding system for estrogens is considered to be responsible for some of the early estrogenic responses, such as water imbibition, histamine releasing and estrogen priming effects.In the present report the fine structure of uterine eosinophils is described. Their pseudopodium-like elongations increase under hyperestrogenic conditions. The eosinophils are found in close proximity to the plasma membranes of other uterine cells. In hyperestrogenic animals, not only is this phenomenon more frequent, but the area of juxtaposition is increased. Pynocytotic vesicles are present in cells adjacent to the eosinophils in the areas of close cellular apposition. The disruption of uterine eosinophils with the liberation of dense granules and specific lysosomes is described. The ultrastructural findings are discussed in relation to the role of uterine eosinophils in the mechanism of estrogen action.