Light microscopic and ultrastructural evidence of epithelial phagocytosis of sperm in the rete testis and ductuli efferentes in the bull.

Light microscopic and ultrastructural observations were made in the bull rete testis and the ductuli efferentes with emphasis on the presence of sperm in the epithelium. Phagocytosed sperm in various stages of degeneration were found in the epithelial cells lining the rete testis and in the nonciliated cells of the ductuli efferentes. Phagocytosis was more prevalent in the rete testis than in the ductuli efferentes. Besides the epithelial cells, degenerating sperm components and residual bodies were in the luminal macrophages of the rete testis. The degeneration of sperm heads presumably progressed in the following order: (i) disruption of the cell membrane, (ii) aggregation of small vesicles, probably of Golgi origin, between the disrupted cell membrane and an outer acrosomal membrane, (iii) loss of the acrosomal matrix, and finally (iv) disintegration of the nuclear chromatin. These degenerative changes probably resulted from increased lysosomal activity of phagocytosing cells. The possible importance and causes of spermiophagy are discussed.