Resorption of the element zinc from spermatozoa by the epididymal epithelium

In this study, elimination of the element zinc from spermatozoa during epididymal maturation was investigated. Testes and epididymides from 40 bulls were collected; epididymal fluid was flushed, pooled, labelled with 0.5 MBq (65) Zn2+ per sample and proteins were separated on a Sephacryl S-200 HR and zinc chelate column chromatography. To follow the resorption of zinc in the epididymal epithelial lining, an autometallographic technique (AMG) was performed in tissue from caput, corpus, cauda and vas deferens. The results showed a zinc-binding protein fraction with an apparent molecular weight of 150-160 kDa, which was enriched after chelate column chromatography. Specific labelling of (65) Zn was about five times higher in the caput than in the cauda epididymidis. AMG revealed no detectable zinc in the caput, but a significant increase of zinc resorption from the corpus to the cauda and vas deferens. Controls showed that the detectable zinc was located within the principal cells. In conclusion, our study proves that zinc present in the sperm flagellum starts to be mobilized in the caput epididymidis and is resorbed by the epididymal epithelium as from the corpus. This zinc elimination is a mandatory step in sperm maturation to obtain motility.