Ultrastructure of the epithelium that lines the ductuli efferentes in domestic equidae, with particular reference to spermatophagy

Abstract

The epithelium that lines the ductuli efferentes in the horse, donkey and mule has been examined by electron microscopy. The epithelium consists of columnar ciliated and non-ciliated cells. Lymphocytes and macrophages are also present, together with cells that are rich in lipofuscin. These 'lipofuscin-rich' cells are a peculiar feature of the excurrent ducts of Equidae and are characterized by a large number of highly heterogeneous residual bodies. The general morphology of the epithelium and, in particular, of the non-ciliated cells implies that the epithelium is involved in the absorption and digestion of luminal fluids. This morphology includes a complex endocytotic apparatus as well as a large and heterogeneous population of lysosomal structures within the cytoplasmic domain. Of particular interest is the unusual presence of peroxisomes. In the Equidae, the cells that compose the epithelial layer appear to act directly on the germinal cells, via the process of spermatophagy. The presence of peroxisomes in non-ciliated cells has been implicated in endocytotic and spermatophagic activities, and peroxisomes may be involved in the oxidation and elimination of toxic peroxides.