The epithelium of uterine biopsies from cyclic dairy cattle: ultrastructure and endocytotic activity.

An ultrastructural description of the epithelium of bovine uterine biopsies obtained during the oestrous cycle, implying lysosome characterization for acid phosphatase by incubation, was undertaken. By means of cationized ferritin (CF) experiments, it was determined whether apical vesicles in the non-ciliated surface epithelial cells were involved in endocytosis. The uterine surface epithelium as well as the glandular epithelium comprised ciliated cells and non-ciliated cells. The non-ciliated cell type performed a cyclic activity implying a higher occurrence of apical vesicles and greater size of the Golgi complexes at 7 and 14 days post-oestrum than at oestrus. This variation was pronounced in the glandular epithelium and less distinct in the surface epithelium. The apical vesicles in the non-ciliated surface epithelial cells were involved in endocytosis. The relative endocytotic activity, i.e., the proportion of CF-labelled structures, was low 7 days post-oestrum and high at oestrus. At the latter cycle stage CF particles were observed in apical vesicles, vacuoles, cisternal structures and bodies of similar morphology such as lysosomes showing reaction products after incubation for acid phosphatase. With increasing incubation time a shift in CF labelling from apical vesicles to lysosomes was noticed.