Hormonal regulation of zona‐binding ability and fertilizing ability of rat epididymal spermatozoa

Abstract

AbstractRat spermatozoa from the proximal caput, the proximal corpus, the middle corpus, and the distal cauda epididymidis were examined for their ability to bind to the zona pellucida after a 1‐, 2.5‐, or 4.5‐h incubation at 34°C with rat eggs in cumulus. Caput spermatozoa did not bind to the zona after 1, 2.5, or 4.5 h of incubation. Corpus spermatozoa did bind to the zona, but the percentage of eggs with bound spermatozoa and number of bound spermatozoa per egg increased with the length of incubation. Cauda spermatozoa bound readily to the zona pellucida, and their zona binding ability did not change with longer incubations. It thus appears that rat spermatozoa gradually acquire the ability to bind to the zona pellucida in the corpus epididymidis.The zona‐binding capacity of cold immobilized cauda spermatozoa, defined as the percentage of eggs with bound spermatozoa, increased with the number of spermatozoa incubated and reached a plateau characteristic of the endocrine status of the animal. After castration, zona‐binding ability is progressively lost from day 3 until day 10 where it is nil. Testosterone supplementation maintains zona‐binding ability to control levels. Similarly, fertilizing ability declines from day 5 after castration until day 10. Testosterone prevents this loss of fertilizing ability. It thus appears that the development of zona‐binding ability during epididymal transit is, like the development of fertilizing ability, under androgen regulation.The close correlation between the onset of fertilizing ability and zona‐binding ability during maturation, the loss of fertilizing ability and zona‐binding ability after castration, and the recovery of both fertilizing ability and zona‐binding ability with testosterone treatment suggests that the androgen‐dependent development of zona‐binding ability is an important component of the acquisition of sperm fertilizing ability during epididymal transit.