Size of rat spermatozoa during maturation along the epididymis

An electrical sizing apparatus based on the Coulter Counter was used to measure rat spermatozoa from the proximal (caput) and distal (caudal) ends of the epididymis and from the ejaculate. The typical size distribution is unimodal with a positive skew, the crescent shape of the cells precluding absolute volume determination. During their passage through the epididymis, spermatozoa decrease in size as part of maturation. Saponin causes cell lysis and chymotrypsin cell shrinkage, both effects being more pronounced in the proximal region. It would seem that, during the maturation process within the epididymis, changes occur in the spermatozoon membrane that make the cells more stable.