Immunocytochemical evidence that a specialised region of the rat oviduct secretes an oviductal glycoprotein.

The immunocytochemical localisation in the rat oviduct of an oviductal glycoprotein was investigated by light and electron microscopy. Using a monoclonal antibody (MAb) that cross-reacted with the rat oviductal glycoprotein ( > 330 kDa), we examined the epithelium of 4 regions (fimbriae, ampulla, isthmus and uterotubal junction) of the rat oviduct during the oestrous cycle. The MAb reacted specifically with the epithelial cells of the rat oviduct and not with the stromal cells. Intense labelling was observed in the isthmic epithelium throughout the oestrous cycle. Immunohistochemical staining was observed in the ampullary epithelium but the reaction was very weak. In the fimbriae and at the uterotubal junction, the immunoreaction was barely apparent in the epithelial cells. At the ultrastructural level, the MAb bound selectively to the putative secretory granules of nonciliated secretory cells in the isthmus, but no labelling was observed in most of the secretory granules in the ampullary segment. These results demonstrate that certain glycoproteins are secreted mainly by the isthmic secretory cells, suggesting regional specificity of the production of the glycoprotein in the rat oviduct.