Fertilization of Denuded Rabbit Eggs in vitro by Sperm recovered from the Uterus or Vagina

Abstract

RECENTLY shed eggs are surrounded by a sticky mass of follicular cells known as the cumulus oophorus. The follicular cells, which are closely attached to the zona pellucida and are arranged in a compact radial pattern, are called the corona radiata. It has been postulated that the follicular cells in the cumulus oophorus can protect the egg against polyspermic fertilization, and can improve the chance of fertilization by providing a large target for the sperm. Further, due to the radial arrangement of the corona radiata, these follicular cells can act in orientating the sperm towards eggs¹. After the dissolution of cumulus oophorus by treatment with hyaluronidase in vitro, however, rabbit eggs can be fertilized when transferred into the tubes of mated rabbits^2,3. After the dissolution of cumulus oophorus and removal of the corona radiata by manual shaking, the denuded eggs can also be fertilized in vitro⁴ or in vivo^5,6. A comparison of the proportion of eggs fertilized in vitro between denuded eggs and those with follicular cells intact has not been made. In addition, it has been speculated that the progesterone present in the follicular fluid or synthesized by the granulosa cells may be necessary for the “acrosome reaction”, capacitation of sperm, and the fertilization of eggs in vitro⁷. The experiment described here demonstrates (1) that denuded rabbit eggs lacking follicular cells (or progesterone) can be fertilized equally as well as intact eggs with cumulus oophorus, and (2) that sperm recovered from the vagina can fertilize rabbit eggs in vitro as well as those recovered from the uterus.