Sperm‐egg ratios and the site of the acrosome reaction during in vivo fertilization in the hamster

Abstract

AbstractLittle is known about the timing of the mammalian sperm acrosome reaction during fertilization in vivo. To study this problem, female hamsters were inseminated at about the time of ovulation, and the contents of the ampullary regions of their oviducts were subsequently examined at various intervals. No living spermatozoa were recovered from ampullae earlier than 4 hr after insemination. The first appearance of living spermatozoa coincided closely with the first appearance of fertilized eggs in the same oviduct. The total numbers of living spermatozoa did not start to exceed the number of eggs in the same ampulla, until after 50% or more of the eggs had been fertilized. Hamster spermatozoa are highly efficient at making contact with eggs, and the fertilizing spermatozoon probably spends no more than 2½ –5½ min in penetrating the cumulus oophorus. Spermatozoa that enter the ampulla appear to be ready to undergo the acrosome reaction, and complete it while they are passing through the cumulus or shortly before, or after, contacting the surface of the zona pellucida.