Development of the fertilizing ability of spermatozoa in the epididymis of the rabbit

Abstract

Abstract When spermatozoa from specific segments of the epididymis were inseminated intra‐tubally, ten hours before ovulation, virtually no ova were fertilized by sperm samples taken from the regions proximal to the middle of the corpus epididymidis. Sperm from the caput epididymidis and the proximal half of the corpus region not only fail to fertilize, but are also apparently unable to establish contact with the surface of the zona pellucida. Although a maximal fertilization rate was obtained with sperm samples from the lower part of the corpus epididymidis, significantly greater numbers of supplementary and zona surface spermatozoa were found in association with tubal ova exposed to similar numbers of sperm from the cauda epididymidis. This latter finding suggests that the cauda region contains a relatively higher percentage of mature spermatozoa, and thus that a proportion of spermatozoa do not become functionally mature until they have passed from the corpus epididymidis. Approximately 7% and 5% of ova exposed to spermatozoa from the lower corpus and cauda regions, respectively, contained three and occasionally four pronuclei, quite probably as a consequence of polyspermic fertilization. As no polyploid ova were found after similar exposure to greater numbers of ejaculated spermatozoa (Adams and Chang, '62), it is conceivable that there may be other systems on the sperm head, as well as those concerned with penetration of the zona, which also mature in some way during epididymal passage.